I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
Please help if you can.
Thanks,
Dave
Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
Good luck,
Meade
:Hello All,
: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:
: Please help if you can.
:
:Thanks,
:
:Dave
Would it make any difference if the speaker is connected to the other end of the secondary where the foot switch would attach? I think that that could be my problem. I'll also try one of the very finest 12AU7s.
I think I may also be able to find that second IF transformer as well.
Thanks,
Dave
:Hi Dave,
:Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:
:If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:
:By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:
:Good luck,
:Meade
:
:
::Hello All,
:: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::
:: Please help if you can.
::
::Thanks,
::
::Dave
All the resistors are the correct value except for the 5.6K ohm (R29) resistor which measures 7.16K ohms. The 5.6 Meg ohm resistor (R28) measures about 168K in circuit. I'm assuming that that's normal. R30 is a bit over 1K. It's supposed to be 910 ohms. That seems normal too. I replaced the 12AU7 with another 12AU7 and it still wont stop on a strong station.
Does this mean it's time to find a replacement IF transformer? What about IF transformer "surgery"? What are the values of those mica capacitors inside?
Thanks,
Dave
:Meade,
: Would it make any difference if the speaker is connected to the other end of the secondary where the foot switch would attach? I think that that could be my problem. I'll also try one of the very finest 12AU7s.
:I think I may also be able to find that second IF transformer as well.
:
:Thanks,
:
:Dave
:
::Hi Dave,
::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::
::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::
::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::
::Good luck,
::Meade
::
::
:::Hello All,
::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::
::: Please help if you can.
:::
:::Thanks,
:::
:::Dave
I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
Thanks,
Dave
:Hi Dave,
:Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:
:If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:
:By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:
:Good luck,
:Meade
:
:
::Hello All,
:: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::
:: Please help if you can.
::
::Thanks,
::
::Dave
Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
Is the second IF transformer in need of replacement? What else should I check?
Thanks,
Dave
:Meade,
: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:
:Thanks,
:
:Dave
:
::Hi Dave,
::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::
::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::
::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::
::Good luck,
::Meade
::
::
:::Hello All,
::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::
::: Please help if you can.
:::
:::Thanks,
:::
:::Dave
I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
Thanks,
Dave
:Meade,
: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
: Is the second IF transformer in need of replacement? What else should I check?
:
:Thanks,
:
:Dave
::Meade,
:: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::
::Thanks,
::
::Dave
::
:::Hi Dave,
:::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::
:::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::
:::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::
:::Good luck,
:::Meade
:::
:::
::::Hello All,
:::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::
:::: Please help if you can.
::::
::::Thanks,
::::
::::Dave
I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
Dave
:Meade,
: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:
:Thanks,
:
:Dave
::Meade,
:: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:: Is the second IF transformer in need of replacement? What else should I check?
::
::Thanks,
::
::Dave
:::Meade,
::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::
:::Thanks,
:::
:::Dave
:::
::::Hi Dave,
::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::
::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::
::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::
::::Good luck,
::::Meade
::::
::::
:::::Hello All,
::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::
::::: Please help if you can.
:::::
:::::Thanks,
:::::
:::::Dave
I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
Meade
:Meade,
: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:
:Dave
::Meade,
:: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::
::Thanks,
::
::Dave
:::Meade,
::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::: Is the second IF transformer in need of replacement? What else should I check?
:::
:::Thanks,
:::
:::Dave
::::Meade,
:::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::
::::Thanks,
::::
::::Dave
::::
:::::Hi Dave,
:::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::
:::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::
:::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::
:::::Good luck,
:::::Meade
:::::
:::::
::::::Hello All,
:::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::
:::::: Please help if you can.
::::::
::::::Thanks,
::::::
::::::Dave
MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
Referencing Schema is ....Right C'here
73's de Edd
:Dave,
:I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:
:If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:
:Meade
:
:
:
::Meade,
:: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::
::Dave
:::Meade,
::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::
:::Thanks,
:::
:::Dave
::::Meade,
:::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::: Is the second IF transformer in need of replacement? What else should I check?
::::
::::Thanks,
::::
::::Dave
:::::Meade,
::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::
:::::Thanks,
:::::
:::::Dave
:::::
::::::Hi Dave,
::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::
::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::
::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::
::::::Good luck,
::::::Meade
::::::
::::::
:::::::Hello All,
::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::
::::::: Please help if you can.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
OK I kind of understand how this works. But I tried 12 volts from the battery connected to pin 2 on the 12AU7. Negative going to the chassis. Should the negative, go to the cathode of that triode if I use a 9v battery to try to turn on the tube? Connecting 12 volts the way I did had no effect whatsoever. The only thing that put a low on the grid of the next triode to shut it off was connecting the grid to the chassis for an instant.
If there's a low on the grid of the first triode, there will be a high on the plate of the first triode which is connected to the grid of the second triode. If there's a high on the grid of the second triode there will be a low on the plate of the the second triode, it will become the negative terminal of the relay coil and it will energize the relay.
When the scan button is pressed, the relay does energize. Is the button sending a high to the grid of the first triode to do this (Pin 2)? Looking at the schematic, it doesn't appear to do that. So how does it energize the relay? This is confusing.
It's getting late here. I'll have to do this tomorrow morning. Thanks for your instructions. So much of this set is working this time, this is going to be a working set. I wont give up.
I hope my old Eico scope works. All I have is a Fluke DVM. I have the 9v battery. I have lots of resistors. I think I can do this.
Thanks Again,
Dave
:
:
:
:
:MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:
:
:
:To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:
:
:Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:
:
:Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:
:
:Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:
:
:Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:
:Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:
:Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:
:
:I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:
:Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:
:
:
:
:Referencing Schema is ....Right C'here
:
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
:
:
::Dave,
::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::
::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::
::Meade
::
::
::
:::Meade,
::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::
:::Dave
::::Meade,
:::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::
::::Thanks,
::::
::::Dave
:::::Meade,
::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::: Is the second IF transformer in need of replacement? What else should I check?
:::::
:::::Thanks,
:::::
:::::Dave
::::::Meade,
:::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::
::::::Thanks,
::::::
::::::Dave
::::::
:::::::Hi Dave,
:::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::
:::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::
:::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::
:::::::Good luck,
:::::::Meade
:::::::
:::::::
::::::::Hello All,
:::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::
:::::::: Please help if you can.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
I don't see how a DC voltage can result from connecting a wire to one end of a diode. The other end of the diode doesn't seem to be in the circuit at all. AC comes through C9, on the other side of C9 the diode and R26 connect to it and DC comes from the the other end of R26? This seems totally impossible to me. Wouldn't the diode have to be in series with the AC coming from C9 and then the resistor connected to the other end of the diode? This is very odd.
Also when I connect the 85 volts from the plate of the 12BF6 directly to pin 2 on the 12AU7 for a split second it immediately stops scanning and stays stopped until the scan button is pressed again. But when I connect little voltages (9 or 12) to pin 2 on the 12AU7 it continues to scan and absolutely refuses to stop. This is an extremely frustrating circuit. Why would anyone design a radio like this without a manual tuning control?
I cannot find a plain old meter. I only have the digital one. The voltages all go negative to pin 2 as it's tuning. This doesn't make any sense either.
Thanks,
Dave
:
:
:
:
:MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:
:
:
:To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:
:
:Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:
:
:Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:
:
:Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:
:
:Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:
:Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:
:Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:
:
:I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:
:Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:
:
:
:
:Referencing Schema is ....Right C'here
:
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
:
:
::Dave,
::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::
::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::
::Meade
::
::
::
:::Meade,
::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::
:::Dave
::::Meade,
:::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::
::::Thanks,
::::
::::Dave
:::::Meade,
::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::: Is the second IF transformer in need of replacement? What else should I check?
:::::
:::::Thanks,
:::::
:::::Dave
::::::Meade,
:::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::
::::::Thanks,
::::::
::::::Dave
::::::
:::::::Hi Dave,
:::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::
:::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::
:::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::
:::::::Good luck,
:::::::Meade
:::::::
:::::::
::::::::Hello All,
:::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::
:::::::: Please help if you can.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
Thanks,
Dave
:
:
:
:
:MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:
:
:
:To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:
:
:Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:
:
:Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:
:
:Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:
:
:Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:
:Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:
:Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:
:
:I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:
:Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:
:
:
:
:Referencing Schema is ....Right C'here
:
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
:
:
::Dave,
::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::
::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::
::Meade
::
::
::
:::Meade,
::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::
:::Dave
::::Meade,
:::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::
::::Thanks,
::::
::::Dave
:::::Meade,
::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::: Is the second IF transformer in need of replacement? What else should I check?
:::::
:::::Thanks,
:::::
:::::Dave
::::::Meade,
:::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::
::::::Thanks,
::::::
::::::Dave
::::::
:::::::Hi Dave,
:::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::
:::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::
:::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::
:::::::Good luck,
:::::::Meade
:::::::
:::::::
::::::::Hello All,
:::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::
:::::::: Please help if you can.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
Play it again !.....SAM…..[CADDY SCHEMA]
Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
and bypassing capacitive oriented components.
You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
pipe line to the AVC and the separate signal seeking / triggering circuitry.
Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
triode pair that are used for the signal seeking trigger mechanism.
Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding”... hoz recurrent sweep versus a
stable triggered sweep design.
Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
In going back to the previously suggested approach:
That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
Standing by for feedback and / or further query.
73's de Edd
:Edd,
: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:
:Thanks,
:
:Dave
::
::
::
::
::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::
::
::
::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::
::
::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::
::
::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::
::
::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::
::
::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::
::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::
::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::
::
::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::
::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::
::
::
::
::Referencing Schema is ....Right C'here
::
::
::
::
::73's de Edd
::
::
::
::
::
::
::
::
::
::
::
:::Dave,
:::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::
:::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::
:::Meade
:::
:::
:::
::::Meade,
:::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::
::::Dave
:::::Meade,
::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::
:::::Thanks,
:::::
:::::Dave
::::::Meade,
:::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::: Is the second IF transformer in need of replacement? What else should I check?
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Meade,
::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::
:::::::Thanks,
:::::::
:::::::Dave
:::::::
::::::::Hi Dave,
::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::
::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::
::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::
::::::::Good luck,
::::::::Meade
::::::::
::::::::
:::::::::Hello All,
::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::
::::::::: Please help if you can.
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
When I try to reply I see the link. However it doesn't show up in the forum.
Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
I am having trouble visualizing it.
Thanks,
Dave
:Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
:
:
:
:Play it again !.....SAM…..[CADDY SCHEMA]
:
:
:
:Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
:
:Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
:and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
:and bypassing capacitive oriented components.
:
:You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
:pipe line to the AVC and the separate signal seeking / triggering circuitry.
:
:Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
:dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
:Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
:triode pair that are used for the signal seeking trigger mechanism.
:Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
:
:
:On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding”... hoz recurrent sweep versus a
:stable triggered sweep design.
:
:
:Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
:In going back to the previously suggested approach:
:
:That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
:That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
:Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
:
:
:Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
:If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
:Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
:
:
:There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
:
:
:
:
:Standing by for feedback and / or further query.
:
:
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
:
:
:
:
::Edd,
:: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
::
::Thanks,
::
::Dave
:::
:::
:::
:::
:::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:::
:::
:::
:::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:::
:::
:::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:::
:::
:::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:::
:::
:::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:::
:::
:::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:::
:::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:::
:::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:::
:::
:::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:::
:::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:::
:::
:::
:::
:::Referencing Schema is ....Right C'here
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
::::Dave,
::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::::
::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::::
::::Meade
::::
::::
::::
:::::Meade,
::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::::
:::::Dave
::::::Meade,
:::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Meade,
::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::::: Is the second IF transformer in need of replacement? What else should I check?
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Meade,
:::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::::
::::::::Thanks,
::::::::
::::::::Dave
::::::::
:::::::::Hi Dave,
:::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::::
:::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::::
:::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::::
:::::::::Good luck,
:::::::::Meade
:::::::::
:::::::::
::::::::::Hello All,
:::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::::
:::::::::: Please help if you can.
::::::::::
::::::::::Thanks,
::::::::::
::::::::::Dave
Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
Thanks for showing all the related components.
Dave
:Edd,
: When I try to reply I see the link. However it doesn't show up in the forum.
: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
: I am having trouble visualizing it.
:
:Thanks,
:
:Dave
::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
::
::
::
::Play it again !.....SAM…..[CADDY SCHEMA]
::
::
::
::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
::
::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
::and bypassing capacitive oriented components.
::
::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
::pipe line to the AVC and the separate signal seeking / triggering circuitry.
::
::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
::triode pair that are used for the signal seeking trigger mechanism.
::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
::
::
::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding”... hoz recurrent sweep versus a
::stable triggered sweep design.
::
::
::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
::In going back to the previously suggested approach:
::
::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
::
::
::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
::
::
::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
::
::
::
::
::Standing by for feedback and / or further query.
::
::
::
::
::
::73's de Edd
::
::
::
::
::
::
::
::
::
::
::
::
::
:::Edd,
::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:::
:::Thanks,
:::
:::Dave
::::
::::
::::
::::
::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::::
::::
::::
::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::::
::::
::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::::
::::
::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::::
::::
::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::::
::::
::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::::
::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::::
::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::::
::::
::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::::
::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::::
::::
::::
::::
::::Referencing Schema is ....Right C'here
::::
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
:::::Dave,
:::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::::
:::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::::
:::::Meade
:::::
:::::
:::::
::::::Meade,
:::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::::
::::::Dave
:::::::Meade,
::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Meade,
:::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::::: Is the second IF transformer in need of replacement? What else should I check?
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::Meade,
::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
:::::::::
::::::::::Hi Dave,
::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::::
::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::::
::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::::
::::::::::Good luck,
::::::::::Meade
::::::::::
::::::::::
:::::::::::Hello All,
::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::::
::::::::::: Please help if you can.
:::::::::::
:::::::::::Thanks,
:::::::::::
:::::::::::Dave
It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
Thanks,
Dave
:Edd,
: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
:
: Thanks for showing all the related components.
:
:Dave
::Edd,
:: When I try to reply I see the link. However it doesn't show up in the forum.
:: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
:: I am having trouble visualizing it.
::
::Thanks,
::
::Dave
:::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
:::
:::
:::
:::Play it again !.....SAM…..[CADDY SCHEMA]
:::
:::
:::
:::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
:::
:::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
:::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
:::and bypassing capacitive oriented components.
:::
:::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
:::pipe line to the AVC and the separate signal seeking / triggering circuitry.
:::
:::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
:::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
:::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
:::triode pair that are used for the signal seeking trigger mechanism.
:::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
:::
:::
:::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding”... hoz recurrent sweep versus a
:::stable triggered sweep design.
:::
:::
:::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
:::In going back to the previously suggested approach:
:::
:::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
:::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
:::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
:::
:::
:::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
:::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
:::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
:::
:::
:::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
:::
:::
:::
:::
:::Standing by for feedback and / or further query.
:::
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
::::Edd,
:::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
::::
::::Thanks,
::::
::::Dave
:::::
:::::
:::::
:::::
:::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:::::
:::::
:::::
:::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:::::
:::::
:::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:::::
:::::
:::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:::::
:::::
:::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:::::
:::::
:::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:::::
:::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:::::
:::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:::::
:::::
:::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:::::
:::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:::::
:::::
:::::
:::::
:::::Referencing Schema is ....Right C'here
:::::
:::::
:::::
:::::
:::::73's de Edd
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
::::::Dave,
::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::::::
::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::::::
::::::Meade
::::::
::::::
::::::
:::::::Meade,
::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::::::
:::::::Dave
::::::::Meade,
:::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::Meade,
::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::::::: Is the second IF transformer in need of replacement? What else should I check?
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::Meade,
:::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::::::
::::::::::Thanks,
::::::::::
::::::::::Dave
::::::::::
:::::::::::Hi Dave,
:::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::::::
:::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::::::
:::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::::::
:::::::::::Good luck,
:::::::::::Meade
:::::::::::
:::::::::::
::::::::::::Hello All,
:::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::::::
:::::::::::: Please help if you can.
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
Also:
R26 specified as an 820k, might be a 1 meg
R3 specified as 910 ohm, might be a 1.1 K
R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
See if that doesn't possibly produce a level up into the 7-16 volts negative range.
Out of time now.....
Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
on a no signal, versus tuned into a strong signal condition.
Edd.....
:Edd,
: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
:
:Thanks,
:
:Dave
:
::Edd,
:: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
::
:: Thanks for showing all the related components.
::
::Dave
:::Edd,
::: When I try to reply I see the link. However it doesn't show up in the forum.
::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
::: I am having trouble visualizing it.
:::
:::Thanks,
:::
:::Dave
::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
::::
::::
::::
::::Play it again !.....SAM?.[CADDY SCHEMA]
::::
::::
::::
::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
::::
::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
::::and bypassing capacitive oriented components.
::::
::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
::::
::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
::::triode pair that are used for the signal seeking trigger mechanism.
::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
::::
::::
::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
::::stable triggered sweep design.
::::
::::
::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
::::In going back to the previously suggested approach:
::::
::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
::::
::::
::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
::::
::::
::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
::::
::::
::::
::::
::::Standing by for feedback and / or further query.
::::
::::
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
:::::Edd,
::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:::::
:::::Thanks,
:::::
:::::Dave
::::::
::::::
::::::
::::::
::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::::::
::::::
::::::
::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::::::
::::::
::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::::::
::::::
::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::::::
::::::
::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::::::
::::::
::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::::::
::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::::::
::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::::::
::::::
::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::::::
::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::::::
::::::
::::::
::::::
::::::Referencing Schema is ....Right C'here
::::::
::::::
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::Dave,
:::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::::::
:::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::::::
:::::::Meade
:::::::
:::::::
:::::::
::::::::Meade,
:::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::::::
::::::::Dave
:::::::::Meade,
::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::Meade,
:::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::::::: Is the second IF transformer in need of replacement? What else should I check?
::::::::::
::::::::::Thanks,
::::::::::
::::::::::Dave
:::::::::::Meade,
::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::::::
:::::::::::Thanks,
:::::::::::
:::::::::::Dave
:::::::::::
::::::::::::Hi Dave,
::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::::::
::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::::::
::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::::::
::::::::::::Good luck,
::::::::::::Meade
::::::::::::
::::::::::::
:::::::::::::Hello All,
::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::::::
::::::::::::: Please help if you can.
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
I will do as you ask. There is no manual tuning control so it's pretty difficult to stop the scan exactly on a station. But I will try.
Thanks again,
Dave
:Only a second available now for this comeback..but there are factory specified options on that resistor being what you have found.....2.7k.
:Also:
:R26 specified as an 820k, might be a 1 meg
:R3 specified as 910 ohm, might be a 1.1 K
:R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
:
:As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
:conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
:sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
:AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
:thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
:Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
:a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
:See if that doesn't possibly produce a level up into the 7-16 volts negative range.
:Out of time now.....
:Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
:on a no signal, versus tuned into a strong signal condition.
:
:Edd.....
:
:
:
:
:
:
:
:
:
::Edd,
:: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
::
::Thanks,
::
::Dave
::
:::Edd,
::: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
:::
::: Thanks for showing all the related components.
:::
:::Dave
::::Edd,
:::: When I try to reply I see the link. However it doesn't show up in the forum.
:::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
:::: I am having trouble visualizing it.
::::
::::Thanks,
::::
::::Dave
:::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
:::::
:::::
:::::
:::::Play it again !.....SAM?.[CADDY SCHEMA]
:::::
:::::
:::::
:::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
:::::
:::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
:::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
:::::and bypassing capacitive oriented components.
:::::
:::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
:::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
:::::
:::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
:::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
:::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
:::::triode pair that are used for the signal seeking trigger mechanism.
:::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
:::::
:::::
:::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
:::::stable triggered sweep design.
:::::
:::::
:::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
:::::In going back to the previously suggested approach:
:::::
:::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
:::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
:::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
:::::
:::::
:::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
:::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
:::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
:::::
:::::
:::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
:::::
:::::
:::::
:::::
:::::Standing by for feedback and / or further query.
:::::
:::::
:::::
:::::
:::::
:::::73's de Edd
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
::::::Edd,
:::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
::::::
::::::Thanks,
::::::
::::::Dave
:::::::
:::::::
:::::::
:::::::
:::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:::::::
:::::::
:::::::
:::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:::::::
:::::::
:::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:::::::
:::::::
:::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:::::::
:::::::
:::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:::::::
:::::::
:::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:::::::
:::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:::::::
:::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:::::::
:::::::
:::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
::::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:::::::
:::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:::::::
:::::::
:::::::
:::::::
:::::::Referencing Schema is ....Right C'here
:::::::
:::::::
:::::::
:::::::
:::::::73's de Edd
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
::::::::Dave,
::::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::::::::
::::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::::::::
::::::::Meade
::::::::
::::::::
::::::::
:::::::::Meade,
::::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::::::::
:::::::::Dave
::::::::::Meade,
:::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::::::::
::::::::::Thanks,
::::::::::
::::::::::Dave
:::::::::::Meade,
::::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::::::::: Is the second IF transformer in need of replacement? What else should I check?
:::::::::::
:::::::::::Thanks,
:::::::::::
:::::::::::Dave
::::::::::::Meade,
:::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
::::::::::::
:::::::::::::Hi Dave,
:::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::::::::
:::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::::::::
:::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::::::::
:::::::::::::Good luck,
:::::::::::::Meade
:::::::::::::
:::::::::::::
::::::::::::::Hello All,
:::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::::::::
:::::::::::::: Please help if you can.
::::::::::::::
::::::::::::::Thanks,
::::::::::::::
::::::::::::::Dave
I have re-replaced the 12BF6 and it made absolutely no difference.
Dave
:Edd,
: I will do as you ask. There is no manual tuning control so it's pretty difficult to stop the scan exactly on a station. But I will try.
:
:Thanks again,
:
:Dave
::Only a second available now for this comeback..but there are factory specified options on that resistor being what you have found.....2.7k.
::Also:
::R26 specified as an 820k, might be a 1 meg
::R3 specified as 910 ohm, might be a 1.1 K
::R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
::
::As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
::conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
::sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
::AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
::thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
::Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
::a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
::See if that doesn't possibly produce a level up into the 7-16 volts negative range.
::Out of time now.....
::Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
::on a no signal, versus tuned into a strong signal condition.
::
::Edd.....
::
::
::
::
::
::
::
::
::
:::Edd,
::: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
:::
:::Thanks,
:::
:::Dave
:::
::::Edd,
:::: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
::::
:::: Thanks for showing all the related components.
::::
::::Dave
:::::Edd,
::::: When I try to reply I see the link. However it doesn't show up in the forum.
::::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
::::: I am having trouble visualizing it.
:::::
:::::Thanks,
:::::
:::::Dave
::::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
::::::
::::::
::::::
::::::Play it again !.....SAM?.[CADDY SCHEMA]
::::::
::::::
::::::
::::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
::::::
::::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
::::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
::::::and bypassing capacitive oriented components.
::::::
::::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
::::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
::::::
::::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
::::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
::::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
::::::triode pair that are used for the signal seeking trigger mechanism.
::::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
::::::
::::::
::::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
::::::stable triggered sweep design.
::::::
::::::
::::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
::::::In going back to the previously suggested approach:
::::::
::::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
::::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
::::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
::::::
::::::
::::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
::::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
::::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
::::::
::::::
::::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
::::::
::::::
::::::
::::::
::::::Standing by for feedback and / or further query.
::::::
::::::
::::::
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::Edd,
::::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::
::::::::
::::::::
::::::::
::::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::::::::
::::::::
::::::::
::::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::::::::
::::::::
::::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::::::::
::::::::
::::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::::::::
::::::::
::::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::::::::
::::::::
::::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::::::::
::::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::::::::
::::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::::::::
::::::::
::::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:::::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::::::::
::::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::::::::
::::::::
::::::::
::::::::
::::::::Referencing Schema is ....Right C'here
::::::::
::::::::
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
:::::::::Dave,
:::::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::::::::
:::::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::::::::
:::::::::Meade
:::::::::
:::::::::
:::::::::
::::::::::Meade,
:::::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::::::::
::::::::::Dave
:::::::::::Meade,
::::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::::::::
:::::::::::Thanks,
:::::::::::
:::::::::::Dave
::::::::::::Meade,
:::::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::::::::: Is the second IF transformer in need of replacement? What else should I check?
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
:::::::::::::Meade,
::::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
:::::::::::::
::::::::::::::Hi Dave,
::::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::::::::
::::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::::::::
::::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::::::::
::::::::::::::Good luck,
::::::::::::::Meade
::::::::::::::
::::::::::::::
:::::::::::::::Hello All,
::::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::::::::
::::::::::::::: Please help if you can.
:::::::::::::::
:::::::::::::::Thanks,
:::::::::::::::
:::::::::::::::Dave
second section of the 12AU7. Pull out your thin diamond dust relay cleaning tool and clean its contacts to confirm that they weren't blobs of silver OXIDE , weren't comtaminated with a
coat of Mojave desert dust or had meece urine dripped upon them. That units grounding action alternatively overides the sensitivity on a tuning scan process or sets up the biasing level on the 1st stage of the
12AU7 stage via that 910 ohm resistor being in circuit.
73's de Edd
:Edd,
: I have re-replaced the 12BF6 and it made absolutely no difference.
:
:Dave
::Edd,
:: I will do as you ask. There is no manual tuning control so it's pretty difficult to stop the scan exactly on a station. But I will try.
::
::Thanks again,
::
::Dave
:::Only a second available now for this comeback..but there are factory specified options on that resistor being what you have found.....2.7k.
:::Also:
:::R26 specified as an 820k, might be a 1 meg
:::R3 specified as 910 ohm, might be a 1.1 K
:::R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
:::
:::As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
:::conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
:::sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
:::AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
:::thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
:::Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
:::a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
:::See if that doesn't possibly produce a level up into the 7-16 volts negative range.
:::Out of time now.....
:::Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
:::on a no signal, versus tuned into a strong signal condition.
:::
:::Edd.....
:::
:::
:::
:::
:::
:::
:::
:::
:::
::::Edd,
:::: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
::::
::::Thanks,
::::
::::Dave
::::
:::::Edd,
::::: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
:::::
::::: Thanks for showing all the related components.
:::::
:::::Dave
::::::Edd,
:::::: When I try to reply I see the link. However it doesn't show up in the forum.
:::::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
:::::: I am having trouble visualizing it.
::::::
::::::Thanks,
::::::
::::::Dave
:::::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
:::::::
:::::::
:::::::
:::::::Play it again !.....SAM?.[CADDY SCHEMA]
:::::::
:::::::
:::::::
:::::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
:::::::
:::::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
:::::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
:::::::and bypassing capacitive oriented components.
:::::::
:::::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
:::::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
:::::::
:::::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
:::::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
:::::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
:::::::triode pair that are used for the signal seeking trigger mechanism.
:::::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
:::::::
:::::::
:::::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
:::::::stable triggered sweep design.
:::::::
:::::::
:::::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
:::::::In going back to the previously suggested approach:
:::::::
:::::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
:::::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
:::::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
:::::::
:::::::
:::::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
:::::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
:::::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
:::::::
:::::::
:::::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
:::::::
:::::::
:::::::
:::::::
:::::::Standing by for feedback and / or further query.
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::73's de Edd
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
::::::::Edd,
:::::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
::::::::
::::::::Thanks,
::::::::
::::::::Dave
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
:::::::::
:::::::::
:::::::::
:::::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
:::::::::
:::::::::
:::::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
:::::::::
:::::::::
:::::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
:::::::::
:::::::::
:::::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
:::::::::
:::::::::
:::::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
:::::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
:::::::::
:::::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
:::::::::
:::::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
:::::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
:::::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
:::::::::
:::::::::
:::::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
::::::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
:::::::::
:::::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::Referencing Schema is ....Right C'here
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::73's de Edd
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::Dave,
::::::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
::::::::::
::::::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
::::::::::
::::::::::Meade
::::::::::
::::::::::
::::::::::
:::::::::::Meade,
::::::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
::::::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
:::::::::::
:::::::::::Dave
::::::::::::Meade,
:::::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
::::::::::::
::::::::::::Thanks,
::::::::::::
::::::::::::Dave
:::::::::::::Meade,
::::::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
::::::::::::: Is the second IF transformer in need of replacement? What else should I check?
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
::::::::::::::Meade,
:::::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
::::::::::::::
::::::::::::::Thanks,
::::::::::::::
::::::::::::::Dave
::::::::::::::
:::::::::::::::Hi Dave,
:::::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
:::::::::::::::
:::::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
:::::::::::::::
:::::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
:::::::::::::::
:::::::::::::::Good luck,
:::::::::::::::Meade
:::::::::::::::
:::::::::::::::
::::::::::::::::Hello All,
:::::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
:::::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
:::::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
:::::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
::::::::::::::::
:::::::::::::::: Please help if you can.
::::::::::::::::
::::::::::::::::Thanks,
::::::::::::::::
::::::::::::::::Dave
I thought it could be dirty relay contacts. Unfortunately, I cannot find my burnishing tool. I'll get one and try that and let you know the results.
Thanks,
Dave
:Wasn't expecting it to be that tube at all. Now I guess that you should answer the question as to the integrity of the SPDT contacts associated with the relay M9 in the plate circuit of the
:second section of the 12AU7. Pull out your thin diamond dust relay cleaning tool and clean its contacts to confirm that they weren't blobs of silver OXIDE , weren't comtaminated with a
:coat of Mojave desert dust or had meece urine dripped upon them. That units grounding action alternatively overides the sensitivity on a tuning scan process or sets up the biasing level on the 1st stage of the
:12AU7 stage via that 910 ohm resistor being in circuit.
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
::Edd,
:: I have re-replaced the 12BF6 and it made absolutely no difference.
::
::Dave
:::Edd,
::: I will do as you ask. There is no manual tuning control so it's pretty difficult to stop the scan exactly on a station. But I will try.
:::
:::Thanks again,
:::
:::Dave
::::Only a second available now for this comeback..but there are factory specified options on that resistor being what you have found.....2.7k.
::::Also:
::::R26 specified as an 820k, might be a 1 meg
::::R3 specified as 910 ohm, might be a 1.1 K
::::R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
::::
::::As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
::::conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
::::sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
::::AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
::::thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
::::Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
::::a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
::::See if that doesn't possibly produce a level up into the 7-16 volts negative range.
::::Out of time now.....
::::Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
::::on a no signal, versus tuned into a strong signal condition.
::::
::::Edd.....
::::
::::
::::
::::
::::
::::
::::
::::
::::
:::::Edd,
::::: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
:::::
:::::Thanks,
:::::
:::::Dave
:::::
::::::Edd,
:::::: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
::::::
:::::: Thanks for showing all the related components.
::::::
::::::Dave
:::::::Edd,
::::::: When I try to reply I see the link. However it doesn't show up in the forum.
::::::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
::::::: I am having trouble visualizing it.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
::::::::
::::::::
::::::::
::::::::Play it again !.....SAM?.[CADDY SCHEMA]
::::::::
::::::::
::::::::
::::::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
::::::::
::::::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
::::::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
::::::::and bypassing capacitive oriented components.
::::::::
::::::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
::::::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
::::::::
::::::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
::::::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
::::::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
::::::::triode pair that are used for the signal seeking trigger mechanism.
::::::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
::::::::
::::::::
::::::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
::::::::stable triggered sweep design.
::::::::
::::::::
::::::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
::::::::In going back to the previously suggested approach:
::::::::
::::::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
::::::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
::::::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
::::::::
::::::::
::::::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
::::::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
::::::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
::::::::
::::::::
::::::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
::::::::
::::::::
::::::::
::::::::
::::::::Standing by for feedback and / or further query.
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
:::::::::Edd,
::::::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::::::::::
::::::::::
::::::::::
::::::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::::::::::
::::::::::
::::::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::::::::::
::::::::::
::::::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::::::::::
::::::::::
::::::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::::::::::
::::::::::
::::::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::::::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::::::::::
::::::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::::::::::
::::::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::::::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::::::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::::::::::
::::::::::
::::::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:::::::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::::::::::
::::::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::Referencing Schema is ....Right C'here
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::73's de Edd
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
:::::::::::Dave,
:::::::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::::::::::
:::::::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::::::::::
:::::::::::Meade
:::::::::::
:::::::::::
:::::::::::
::::::::::::Meade,
:::::::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::::::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::::::::::
::::::::::::Dave
:::::::::::::Meade,
::::::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
::::::::::::::Meade,
:::::::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::::::::::: Is the second IF transformer in need of replacement? What else should I check?
::::::::::::::
::::::::::::::Thanks,
::::::::::::::
::::::::::::::Dave
:::::::::::::::Meade,
::::::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::::::::::
:::::::::::::::Thanks,
:::::::::::::::
:::::::::::::::Dave
:::::::::::::::
::::::::::::::::Hi Dave,
::::::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::::::::::
::::::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::::::::::
::::::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::::::::::
::::::::::::::::Good luck,
::::::::::::::::Meade
::::::::::::::::
::::::::::::::::
:::::::::::::::::Hello All,
::::::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::::::::::
::::::::::::::::: Please help if you can.
:::::::::::::::::
:::::::::::::::::Thanks,
:::::::::::::::::
:::::::::::::::::Dave
A nice large spray of GC De-Ox-Id on the relay contacts and voila, it stops on strong stations, You were correct. The contacts were dirty. No burnishing tool was necessary for this one though.
When I set the tabs to a particular strong station, all I hear is a scraping sound and the tuning doesn't stop there. I might be pressing the wrong push button. Maybe that board need a good spray as well.
This is fantastic. I believe that the problem is solved.
Thanks very much,
Dave
:Wasn't expecting it to be that tube at all. Now I guess that you should answer the question as to the integrity of the SPDT contacts associated with the relay M9 in the plate circuit of the
:second section of the 12AU7. Pull out your thin diamond dust relay cleaning tool and clean its contacts to confirm that they weren't blobs of silver OXIDE , weren't comtaminated with a
:coat of Mojave desert dust or had meece urine dripped upon them. That units grounding action alternatively overides the sensitivity on a tuning scan process or sets up the biasing level on the 1st stage of the
:12AU7 stage via that 910 ohm resistor being in circuit.
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
::Edd,
:: I have re-replaced the 12BF6 and it made absolutely no difference.
::
::Dave
:::Edd,
::: I will do as you ask. There is no manual tuning control so it's pretty difficult to stop the scan exactly on a station. But I will try.
:::
:::Thanks again,
:::
:::Dave
::::Only a second available now for this comeback..but there are factory specified options on that resistor being what you have found.....2.7k.
::::Also:
::::R26 specified as an 820k, might be a 1 meg
::::R3 specified as 910 ohm, might be a 1.1 K
::::R35 specified as a 1.8K 2 watt unit...also shows a 2.7 K-2 watt plus a 5.6K-2W being placd in parallel and deriving a 4 watt rating.
::::
::::As far as the plate RF voltage on the IF amp tubes being coupled over to the diode detector and all of its + going nodes being
::::conducted and thus stripped off, that would only leave the negative nodes present to then be integrated by filtering and then
::::sent down the line I mentioned. You have seen it being done for the last 'hunna' lebenteen years in the conventional detector
::::AVC circuitry, whereupon the high end of the IF transformers secondary feeds to a detector plate. Then you are doing the same
::::thing when you are then extracting the negative voltage from the lower...cold end of that IF transformers secondary.
::::Since they apparently wanted a much heftier voltage to be created, was possibly the reasoning for the configuration used. Place
::::a high z metering probe ...ground referenced...on either side of that that 820K and confirm, while you tune onto a strong signal.
::::See if that doesn't possibly produce a level up into the 7-16 volts negative range.
::::Out of time now.....
::::Find out that voltage for me as well as the amount that both voltages on the cathodes of the RF and IF tubes are swinging between
::::on a no signal, versus tuned into a strong signal condition.
::::
::::Edd.....
::::
::::
::::
::::
::::
::::
::::
::::
::::
:::::Edd,
::::: It says 3.3K in the parts list. I don't see what difference it would make to go from 2.7K to 3.3 but I'll try it. The one with the mechanical problem also has the 2.7 K instead of the 3.3 K. All the other components have been checked or replaced. All paper and electrolytic capacitors have been replaced. Booth 100pf capacitors which you have marked as critical, have been replaced. The 12AU7 has been replaced 3 times. I have a 12BF7 on order. Maybe the diode is weak. My TV-7 tube tester says that all the tubes are good. All the connections are good. If the developed voltage is negative then from what I see, it will keep the scan going and it will never stop. This doesn't make sense either. The only think that makes the relay de-energize is to put a large positive voltage on the grid of the first tube in the trigger. I have a good car antenna attached to the radio and the signal is very strong. Yet it continues to scan right past the stations. What should I look for next?
:::::
:::::Thanks,
:::::
:::::Dave
:::::
::::::Edd,
:::::: Now that I have seen your schematic, I find that R15 is a 2.7K (Red-Violet-Red) ohm resistor and not a 33K ohm resistor, as the schematic clearly shows. Could that cause any trouble? I'll try a 33K and let everyone know.
::::::
:::::: Thanks for showing all the related components.
::::::
::::::Dave
:::::::Edd,
::::::: When I try to reply I see the link. However it doesn't show up in the forum.
::::::: Thanks, I'll check the resistors you have marked. Some I didn't think of. Could you please make a simplified picture showing where the ac comes from and where the dc is created. It still doesn't make sense to me. How can one side of a diode turn ac into dc as it passes that connection? I don't think that this is what's happening. But that's what it looks like.
::::::: I am having trouble visualizing it.
:::::::
:::::::Thanks,
:::::::
:::::::Dave
::::::::Looks like this topic dropped ever so far down, I didn't even notice your comeback until today. As for your referencing. I checked it out, and the info link to the schematic is still "hot" and active.
::::::::
::::::::
::::::::
::::::::Play it again !.....SAM?.[CADDY SCHEMA]
::::::::
::::::::
::::::::
::::::::Please note however, that my referenced "boxes" were, in actuality, small colored squares in the proximity of suspect parts.
::::::::
::::::::Not my usual larger sizings of markups, by virtue of the larger quantity of components being referenced to this time. The red
::::::::and orange color codings are being relevant to resistive components, while the green coding was for line filtering, coupling
::::::::and bypassing capacitive oriented components.
::::::::
::::::::You apparently missed out on the operative aspect of the developed biasing voltage that is routed down thru the "Fuscia"
::::::::pipe line to the AVC and the separate signal seeking / triggering circuitry.
::::::::
::::::::Reviewing again....starting up at the IF stage, at its plate circuit, there is one healthy level of RF coupled over via C9 to a
::::::::dedicated detector plate in V4. All of the positive RF nodes are stripped off by that rectifying action, thereby only leaving a developed ---NEGATIVE--- voltage going over to, then down the "Fuscia pipeline"... it is initially being received by a 820k resistor, with that DC level receiving a HF stripping by C10 and the voltages further passes on down to a load resistor at R27.
::::::::Traveling to the left down the buss, the control voltage is routed directly to the control grid of the first section of the
::::::::triode pair that are used for the signal seeking trigger mechanism.
::::::::Simultaneously that voltage node is additionally tapped off via R6 and used to feed the conventional AVC control voltage to the mixer and RF front end stages. One variant, on the signal seeking design, is the provision of tailoring the overall gain of the RF and IF amp stages by the alteration of their cathode biasing via the cluster of resistors utilized in the "sensitivity" switch settings.
::::::::
::::::::
::::::::On your comeback on your scope...if I vaguely remember, your unit is a 460 EICO...which, if it is that model, would NOT suffice in this application. as it is a bare bones performance unit, AC coupled in its VERT amp stages..not the required DC..along with lack of dedicated Vert calibration, and the utilization of “slippy- sliding?.. hoz recurrent sweep versus a
::::::::stable triggered sweep design.
::::::::
::::::::
::::::::Unless you can borrow an adequate scope unit, it will require dependency upon common DC metering and using strong RF signals for the comparing of neg DC levels created by the receiver to the triggering threshold level required in the V7 circuitry.
::::::::In going back to the previously suggested approach:
::::::::
::::::::That being the initial lifting of the sets connection that is made to #2-1st grid of V7 .
::::::::That is being done in order to, instead, be applying a ground referenced NEGATIVE voltage to the pin #2-1st grid of V7 to determine exactly what voltage threshold is required for seek stop activation..
::::::::Start the unit on a seeking scan and bring up the level of applied test bias to see what voltage threshold level is required to initiate a seek latch.
::::::::
::::::::
::::::::Then you pull the test biasing and re-connect the original connection of pin #2-1st grid of V7 back as it was and then reinitiate a seek and monitor that grid to see if it triggers on signal threshold...or how far deficient the developed signal is being , in reference to the prior established triggering threshold.
::::::::If it never can develop that threshold level, confirm it is not due to the initial consideration of underperforming RF IF tubes or an ALIGNMENT deficiency , with its resultant of its limiting max developed voltage or a final need to confirm that the resistive components designated , might be out of spec.
::::::::Another consideration would be the capacitive units being leaky. (Or caps being of very low value, if being used in the screen or cathode bypass functions.)
::::::::
::::::::
::::::::There would be a like checkout of the V7 circuits resistive values incorporated in its K-P and 1stG- K circuitry , as they are configuring the DC coupled unit such as to have a more distinct "snap action" of the triggering threshold by their utilization as creating a quasi- monostable multivibrator.
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::::::::Standing by for feedback and / or further query.
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::::::::73's de Edd
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:::::::::Edd,
::::::::: I cannot find the red, green and orange boxes you mention. I think I'm missing a link to them.
:::::::::
:::::::::Thanks,
:::::::::
:::::::::Dave
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::MMmmmmmm '55 Catterack car radio ?.....schmitt...und....Vunderbarrr...no less !
::::::::::
::::::::::
::::::::::
::::::::::To test both the DC amp and the relay driver circuitry in conjunction, hows about subbing in a variable bias voltage from either a bench power supply via the isolation provided by a series in line 10K resistor.
::::::::::
::::::::::
::::::::::Or..... on the simpler side, if no PS is available take a common rect 9V transistor battery and clip leads to a 50k/100k/500k, (what have you) pots outer ends and then output from its center wiper , it being the output, and one bottom outer terminal becoming a common for your vari-supply output ( with the same mentioned 10k isolation resistor in line with the center terminal) .
::::::::::
::::::::::
::::::::::Now, that gives you an adjustable voltage to simulate the detected voltage off the set, that it uses for sensing.
::::::::::
::::::::::
::::::::::Check out the supplied schema for referencing , there you will see the high level IF RF at the plate of V3 being coupled via C9 to one of the 12BF6 diode elements for rectificaton and and initial feed out of that developed voltage thru R26 and then track it on down the " fuscia brick road " , with it having a couple of voltage divisions, one at R27 and also at the left over at R3-5-7 for the AVC for the RF and mixer stages.
::::::::::
::::::::::
::::::::::Then for testing you go down to the 1st grid of the 12AU7 (pin 2) and clip in that voltage and initially have that voltage pot at its minumum level and start the radio into a seeking scan and then bring up the bias to see what threshold is required to enact a scan "stop" condition . BTW.....this may take several attempts to come up with an "average" triggering level threshold.
::::::::::Now you know what sensing level of voltage is required...as well as also confirming the electro mechanic interfaces functioning properly.
::::::::::
::::::::::Needless to say, that the metering should be a Hi z, such as offered by VTVM, FET-VM or DVM...however I prefer the prior two...due to no digit bobbling.....and the nuance variances, being so downright noticable on an analog's readout.
::::::::::
::::::::::Once you have that threshold figure, strip off connections and get the radio back in its initial state and then take readings of the voltage being developed at pin 2 as the unit scans across the band, needless to say, by virtue of the fast DC level shifting , that would be done by monitoring this time with a scope and setting it into its DC coupled mode and sloooowing down the Hoz timebase into its 100's of milliseconds sweep rate speed.
::::::::::Set the vertical centering such that center graticule is your O VDC referencing, and then go over and scope probe pin 2 ...cathode of V4 so that you can get its 10 VDC voltage referencing level and set up your vertical sensitivity such that the scope trace is up 2 divisions but not off scale.
::::::::::Then as you scope probe monitor pin 2 of the 12AU7 when initiating a seek, you can then see the slow moving scope trace bobbling up and down in accordance to the detected DC voltage levels of different stations as it seeks and then you can make an evaluation of the degree if defiency that voltage present is from the level that you previously required to initiate a stop action in your earlier testing.
::::::::::
::::::::::
::::::::::I have redboxed critical resistor values for this circuitry as well as orange boxed units associated with the gain stage of the RF amp and finally critical coupling or bypassing caps in green boxes....NO leakee-leakee.
:::::::::: There are also the final apparent problem conditions of low gain in RF or IF tubes or mis alignment in the RF or IF stages circuitry..
::::::::::
::::::::::Or another possible problem, being in the 12AU7 direct DC coupled circuitry, with some of its resistors being off in value.
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::Referencing Schema is ....Right C'here
::::::::::
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::::::::::73's de Edd
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:::::::::::Dave,
:::::::::::I don't have a wonder-bar handy to check out, but I believe the voltages on pin 2 should be negative in operation. When you ground the wire between pin 1 and 7, you are effectively doing what the 1st. (trigger detector) section of the 12AU7 is supposed to do when a station is found, so the 2nd. (trigger relay) section is doing it's job and the relay drops out, stopping the search function. This means that the 1st. section is not working as designed, probably because the signal from the secondary of the 2nd. I.F. is not strong enough to trigger the tube. There are two small (100mmf) capacitors between the I.F. and pin 2 of the 12AU7 (C9 and C10 if you are using Sams AR-6), but they are most likely okay. I still suspect either a bad I.F. transformer or the I.F.'s needing alignment.
:::::::::::
:::::::::::If you are going to replace the micas in the base of the I.F., I would try different silver mica caps in the range of 80 to 120mmf across the secondary (whatever it takes to allow resonance at 262kc), and smaller caps for the other two network caps, maybe 10 to 30mmf. (again, whatever works). One is from high side of volume control to ground, and the other will either be across R-16 or from the other side of the I.F. secondary to ground. I don't remember just where the second cap goes, kind of hard to tell from the mica sheets in the base just what capacity is present at what point. I have done them in the past, but I didn't take notes, and my memory has failed me.
:::::::::::
:::::::::::Meade
:::::::::::
:::::::::::
:::::::::::
::::::::::::Meade,
:::::::::::: I'm wrong again. The wire connecting pin 1 to pin 7, passes a center pin, which is connected to the chassis. If I momentarily connect that wire to the chassis, the scan stops and stays stopped.
:::::::::::: That makes sense. Sorry about all the posts. Maybe there's dirty relay contacts.
::::::::::::
::::::::::::Dave
:::::::::::::Meade,
::::::::::::: I made a mistake, that's pin 7 the grid I'm touching with my meter probe (the grid). Not pin 8. The other probe doesn't need to attach to anything. Just move the probe on the pin, draw a less than 1mm arc, and the scan stops instantly. The scan is never muted. The sound is on full when it scans. Could that be dirty contacts?
:::::::::::::
:::::::::::::Thanks,
:::::::::::::
:::::::::::::Dave
::::::::::::::Meade,
:::::::::::::: Applying a positive voltage (12 v from the battery) to pin two has absoutely no effect at all. It does nothing. It still continues to scan. But when I try to measure pin 8 (a cathode) of the 12AU7 and move the probe until I see a tiny spark, the scanning stops instantly, every time. This makes no sense. How can measuring the cathode voltage stop the current from flowing and de-energize the relay?
:::::::::::::: Is the second IF transformer in need of replacement? What else should I check?
::::::::::::::
::::::::::::::Thanks,
::::::::::::::
::::::::::::::Dave
:::::::::::::::Meade,
::::::::::::::: I have negative voltages on pin 2 of the 12AU7. When the relay is de-energized it's -5 volts. When it's tuning, it fluctuates from 0 to about -1.5. I checked my meter leads to make sure they wern't hooked up backwards, but the voltages are negative. Could the caps in the IF transformer do that?
:::::::::::::::
:::::::::::::::Thanks,
:::::::::::::::
:::::::::::::::Dave
:::::::::::::::
::::::::::::::::Hi Dave,
::::::::::::::::Try changing the 12AU7 trigger tube even if it tests good. Check the cathode resistors on the 12AU7, (1k between one cathode and a relay contact, 47k between the other cathode and the relay coil--wouldn't hurt to check the 47k from this cathode to ground also).
::::::::::::::::
::::::::::::::::If the tuner stops seeking (relay drops out) when you jump a positive voltage to pin 2 of the 12AU7, the problem is probably a bad 2nd. IF transformer--maybe silver mica disease?? I had several Delco signal-seekers that replacing the 2nd.IF was the only thing that fixed the "not stopping on stations" problem. A Miller K-Tran 15H-6 is a suitable replacement, but probably just as hard to find as the Delco 1220204.
::::::::::::::::
::::::::::::::::By the way, the push-button tabs have to be positioned on a station frequency or the tuner will not stop at that tab when the push-button for that station is pressed.
::::::::::::::::
::::::::::::::::Good luck,
::::::::::::::::Meade
::::::::::::::::
::::::::::::::::
:::::::::::::::::Hello All,
::::::::::::::::: I know that this is a common problem but I don't remember where to look. As the sensitivity control is adjusted in one direction it lowers the signal and the volume goes down a little bit. Is this normal?
::::::::::::::::: All paper and filter capacitors have been replaced. Even if a station is super strong it wont stop seeking. Also, when it reaches a preset location you can hear the click of the contacts but that wont stop it either. I tested all the tubes on a TV-7 tube tester and it says that they're fine. Where should I look next.
::::::::::::::::: My AR-6 fell apart and I cannot find the SAMs for this set anymore. I can look at a similar set in volume 5 but I don't think it's the same. The tubes are different. This is not the set with the bad ratchet. This ratchet is fine. The return solenoid works perfectly as well.
::::::::::::::::: I can energize the relay but I cannot de-energize it. So this is an electronic problem (a normal problem with signal seekers).
:::::::::::::::::
::::::::::::::::: Please help if you can.
:::::::::::::::::
:::::::::::::::::Thanks,
:::::::::::::::::
:::::::::::::::::Dave