http://www.nostalgiaair.org/Resources/451/M0015451.htm
Ian
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:http://www.nostalgiaair.org/Resources/451/M0015451.htm
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:Ian
Changing the socket resistor or the 2.2 meg did nothing.
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It is unfortunate that this radio has 'fluffed' the tube count by using 2 6H6s where 1 would suffice. If you study the circuit carefully, you'll notice that each of the 6H6s has one side completely grounded and unused. At least with the extra tube they could have done something more elaborate like have full wave detection or something. Eh, not the first time this has been done, though. Even the most prestegious companies unnecessarily increased tube count.
T.
You can also change R19 to a 1Meg potentiometer. Adjust so that the 1st AF doesn't overload on strong signals. The increased resistance here will increase the voltage available to the eye tube.
t.
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:You can also change R19 to a 1Meg potentiometer. Adjust so that the 1st AF doesn't overload on strong signals. The increased resistance here will increase the voltage available to the eye tube.
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:t.
c46 good
c46 was replaced
I changed the value of r19 (paralelled it with larger and smaller values) no change
Coil is good.
no change
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T.
T.
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:T.
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R19 and r 18 are inaccessable , they are inside the coil form.
When I touch the grid of the eye tube it closes all the way when I am grounded, though capacitence or contact with the floor. I attached my scope to the grid, there is signal , and it is changing (to audio). When attached to the probe and the scope is grounded ( to ground) but not to the chassis it closes. When scope is grounded, and chassis is grounded the eyes dosen't change.
I remember the eye working a few weeks ago , when I started this.
Ian
Of course there are dozens of other reasons as to why the eye tube doesn't work properly. Assume that the radio was designed well, and that the eye tube closed properly from the factory, though if necessary, modifications can be made to improve performance. Not all radios were designed properly. The circuit used in this radio to drive the eye tube does not use conventional component values (what are found in many other radios), so it will be difficult to determine how the eye tube should function until we are sure that all components are functioning properly. You should consider removing the IF transformer so that you may measure the values of the resistors inside.
T.
There is negative voltage, 6h6 is good, the eye moves but barely.
:If the eye tube worked a while ago, then you might want to check to see if you miswired anything. The eye will close whenever a negative signal is applied to its control grid. Be sure that the detector 6H6 is functioning properly. Does the radio sound fine? Did you do anything to the eye tube wiring? Often the cathode is tied to one of the heater wires, and this wire is connected to the radio chassis, to which also one side of the filament transformer is connected. If you accidently reversed the heater wires to the eye tube, AC would be injected to the cathode circuit, that might adversely affect eye tube performance.
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:Of course there are dozens of other reasons as to why the eye tube doesn't work properly. Assume that the radio was designed well, and that the eye tube closed properly from the factory, though if necessary, modifications can be made to improve performance. Not all radios were designed properly. The circuit used in this radio to drive the eye tube does not use conventional component values (what are found in many other radios), so it will be difficult to determine how the eye tube should function until we are sure that all components are functioning properly. You should consider removing the IF transformer so that you may measure the values of the resistors inside.
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:T.
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Otherwise, if you absolutely cannot find any trouble, the modifications I suggested may help.
T.
The 1 meg pot in place of R19 only controlled volume, and I wasnt able to get any stations.
I will reassemble and move tomorrow
I think that The 2nd detector is full wave, because both sides are used. Both parts of one diode do not go to ground.
Ian
:Try connecting a nice long antenna to the radio. Also, did you originally operate the radio in a different location? Reception might have been better there, if so.
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:Otherwise, if you absolutely cannot find any trouble, the modifications I suggested may help.
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:T.
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::T.
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:R-18 has drifted up to 60k (4000)
:R19 and r 18 are inaccessable , they are inside the coil form.
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:When I touch the grid of the eye tube it closes all the way when I am grounded, though capacitence or contact with the floor. I attached my scope to the grid, there is signal , and it is changing (to audio). When attached to the probe and the scope is grounded ( to ground) but not to the chassis it closes. When scope is grounded, and chassis is grounded the eyes dosen't change.
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:I remember the eye working a few weeks ago , when I started this.
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:Ian
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Hi Ian and Tom,
I looked over your postings and found "R-18 has drifted up to 60k (4000)." Isn't that important?
If it should be 4K and is 60K this can cause the problem. Did I miss something?
Best Regards,
Bill Grimm
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:::T.
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::R-18 has drifted up to 60k (4000)
::R19 and r 18 are inaccessable , they are inside the coil form.
::
::When I touch the grid of the eye tube it closes all the way when I am grounded, though capacitence or contact with the floor. I attached my scope to the grid, there is signal , and it is changing (to audio). When attached to the probe and the scope is grounded ( to ground) but not to the chassis it closes. When scope is grounded, and chassis is grounded the eyes dosen't change.
::
::I remember the eye working a few weeks ago , when I started this.
::
::Ian
::
:Hi Ian and Tom,
: I looked over your postings and found "R-18 has drifted up to 60k (4000)." Isn't that important?
: If it should be 4K and is 60K this can cause the problem. Did I miss something?
:
:Best Regards,
:
:Bill Grimm
No, it went up by 4000 its supposed to be 56,000
I think I will try to boost R19 later or tomorrow.
What about a cathode resistor on the 6e5? would that do anything?
Ian
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Bringing R18 back down to 58K from 60 might actually make a bit of difference, considering that it is feeding a low value shunt of only 250K (R19).
Regarding a 1Meg pot in place of R19, stations shouldn't go away with the substitution of this resistor if it is wired in correctly, but yes, it will control volume. The eye should be more responsive. The eye grid should be connected where one end of the 1Meg pot connects to the 56K resistor. The AF grid should be connected to the center terminal of the pot, and the other end of the pot should be connected to the radio's chassis. Adjust for maximum volume without distortion on strong stations. This may or may not improve eye performance. It will increase the overall available signal voltage, but will have more of a notable effect on bass than treble. What's used to create the eye signal is actually a very high frequency (the IF), and this might not be affected much at all, but it's worth a try.
Since you say that the eye still hasn't changed with this modification, I am wondering if the grid wire to the eye tube has broken somewhere. Check its continuity.
Regarding the 6H6, from what I see in the schematic, full wave detection is not used, and only one of the two diodes is used. Actually, this really has nothing to do with the performance of your eye tube, but was just one of my typical random unrelated observations. I should not have made mention of it.
If, no matter what you do, you cannot make the eye more responsive, you might also consider connecting it to the actual AVC circuit. It might be stronger than the signal available at the detector, though it appears to receive a similar amount of amplification.
T.
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:Bringing R18 back down to 58K from 60 might actually make a bit of difference, considering that it is feeding a low value shunt of only 250K (R19).
:
:Regarding a 1Meg pot in place of R19, stations shouldn't go away with the substitution of this resistor if it is wired in correctly, but yes, it will control volume. The eye should be more responsive. The eye grid should be connected where one end of the 1Meg pot connects to the 56K resistor. The AF grid should be connected to the center terminal of the pot, and the other end of the pot should be connected to the radio's chassis. Adjust for maximum volume without distortion on strong stations. This may or may not improve eye performance. It will increase the overall available signal voltage, but will have more of a notable effect on bass than treble. What's used to create the eye signal is actually a very high frequency (the IF), and this might not be affected much at all, but it's worth a try.
:
:Since you say that the eye still hasn't changed with this modification, I am wondering if the grid wire to the eye tube has broken somewhere. Check its continuity.
:
:Regarding the 6H6, from what I see in the schematic, full wave detection is not used, and only one of the two diodes is used. Actually, this really has nothing to do with the performance of your eye tube, but was just one of my typical random unrelated observations. I should not have made mention of it.
:
:If, no matter what you do, you cannot make the eye more responsive, you might also consider connecting it to the actual AVC circuit. It might be stronger than the signal available at the detector, though it appears to receive a similar amount of amplification.
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:T.
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T.
This stage is running at full gain , and not being held back, as the upper 2nd IF stage is, with its reduced
This time we are are interested in a gradual decrease of the gain of the RF stages, with that being stretched a
ASIDE: * * * If it is being appreciably higher , whip thru the stations on the dial and leave it tuned in to the strongest station.
ASIDE: * * *
Standing by for exploratory updating . . . or ?'s.
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RCA Mark-UP . . . . . . Working SCHEMATIC:  |
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: : : : : : : :Sir Ian . . . . . : : :Ohhhhh Tayyyy . . . I started on this reply days ago but just now found time for its completion, :and some of its points have been lightly touched upon since its initiation, so I am just going let it :all rip, in its entirity. : : :Indeed that set of yours was quite state of the art at its early time period with all of its features, :with some particular note to its dedicated and separate AVC system. : : :What I might note initially, was your comment as to the eye tube "working" on day one, but not :confirming, as in remembering for sure, if it closed completely on strong stations. : : :If so, I also think of some fault concerning circuit work, since that time, created the present problem. : :Specifically, the creation of adequate sound from the set is not inclusive of having good /high enough gain thru the RF and IF system so as to ensure a healthy DC level output from the detector stage(s). : : :AND that degree of detected DC voltage level is that which is used to feed to the eye tube circuitry. : : :Reference the Marked- Up Schema: : : : :Take note of the detector section marked up in [AQUA] at reference [ F ] there is the AUDIO content :which zips on up to the 6C5 audio stage and the DC componemt present is hi Z isolated a bit with the :R-20 . . .2.2 meg and its .01 ufd , which adds a bit of hang time to changes made while tuning in to a station. : : :That negative voltage level changes the degree of response of your eye tubes pattern. STRONG signal :from the station, more negative voltage developed and more response from your eye tube. : : :This might now be a good time to give JUST the eye tube circuitry an evaluation. : : :(And you do have a 1 meg resistance unit in the eye tube socket . . plate to target . . . right ? ) : : :I usually suggest that one gets a 9V battery and connect across a 1 meg pots outer terminals and then :run a 1 K "stopper" resistor off from that pots center /rotor terminal. : : :That then gives one a variable source of negative voltage as referenced between the + terminal of the :battery and that outer connection of the 1K limiter resistor. : : :HOWEVER, in your situation you have a "fresh" source of negative voltage present DOWN / bottom/left at the power supply at the [YELLOW] - [V] reference. : : :What say we now lift the 2.2 meg resisitor R20 from its [AQUA] reference [ F ] connection and then take a clip lead and connect the floating 2.2 meg to that negative voltage source at - [V] and fire up the set and see what degree of :response the eye tube is now providing. : : :If now responding, far better than initially, we just now have to back track to the simple [ F ] source of the eye tubes negative sensing voltage and take a negative voltage measurement to see exactly what DC level IS being present on that supply point. : : :Look for your very strongest stations, as the maximum voltage at [ F ] will be present on those same stations, then compare that max voltage to what you are reading at the -V supply, that will be the difference that the voltage from the detector will have to be increased to, in order to get the like response of the eye tube. : : :( Out in left field question . . was any alignment done to the receiver ? Particularly the IF stages . . .or any remote chance the unit was aligned to 455/6 instead of 470 ?) : : :O.K. then . . . the next analysis step would be monitoring of [ F ] for its neg voltage level and tune in too :the STRONGEST station that you can receive, and then make a duo directional micro movement (1/4 turn ? )of the 6 separate trimmer caps of the 1st/2nd/3rd IF transformers to see if that -voltage level can be brought up any higher. :Leave each at the peak voltage output . : : :Did that bring up your available detected voltage up closer to that prior ascertained requirement of the eye :tube ? : : :If not, then lets look at another aspect of the receiver, its quite refined AVC system: : : :That circuitry signal flow has been highlighted in [ BLUE ] and [ GREEN ] on the schema referencing. : : :On examining of the 1st grid circuitry of the 2nd IF stage, we see a sampling of the moderately high level of :470 IF signal by the [BLUE ] line which goes down to C66 to be coupled into the the dedicated IF stage amp. : : :This stage is running at full gain , and not being held back, as the upper 2nd IF stage is, with its reduced :screen voltage. The sharpness of IF tuning has already been established by the multiple stages of the main :IF 's, so this RF stage is broad tuned with no concern given to its tuning. : : :Signal flow is being designated by the blue squares path. : : :After detection by the AVC 6H6, the AVC control voltage is dumping into load resistor R37 and having a bit higher level present across a 150, 000 load vice the typical 47K, then the flow down to the R36 and its .O5 summing capacitor, which gives a bit longer decay time for the AVC system, than was present back on the eye tubes supply at [F]. : : :The resultant AVC flow is down the [GREEN] busses and their individual isolation resistors and EACH associative decoupling capacitor, with a whole BUNCH of them being present on that AVC buss with NONE of them wanting to be exhibiting ANY leakage to ground. Or elso you can just kiss your system AVC's dynamic range swing . . . goodbye. : : : :This time we are are interested in a gradual decrease of the gain of the RF stages, with that being stretched a :bit more with those stages also having further resistive isolation and their .05 capacitors associated with :them. : : :What I might ask you to try now is to monitor [BLACK] # 1 reference, for that detected AVC DC voltage and :see how negative it is, as compared to the equivalent [ F ] test point we just measured earlier? : : : :ASIDE: * * * : : : :If it is being appreciably higher , whip thru the stations on the dial and leave it tuned in to the strongest station. : : :Then, I think that you still have the R20 2.2 meg resistor end available for us, so take a clip lead and jumper :between it and the [BLACK] # 1 AVC source to now see how the eye tubes responds using your AVC voltage :as its drive. : : :One final thought, on these tests, if the original eye tube driving voltage never came up at ref [ F ], I now hope that you are equally :knowledgeable / stocked in cross technology apart from these "old radios" and also happen to have a 1N4148 / 1N914 diode available in your parts cache to shunt across the "top" 6H6 such that its anode goes to the plate connection and its cathode goes to ground. Then, see what the detected voltage level hops up to. : : :( If having none of those above diodes, even a "slow" common 1N4001-thru- 4007 "power" diode would do in this pinch. ) : : : : : : :ASIDE: * * * : : :[ BTW back to the use of two 6H6, for plain 1/2 W detection circuitry on BOTH units with unused elements grounded . . . no exotica involved, such as voltage doubling. : : :As for not cross sharing of a 6H6 diode for EACH circuit, I suspicion the detrimental effect of intra stage cross wiring spread out and potential feedback effects from the capacitance proximity in doing that. ) : : : : : : : : :Standing by for exploratory updating . . . or ?'s. : : : : : : : : : :73's de Edd : : : : |
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: : : :RCA Mark-UP . . . . . . Working SCHEMATIC: : : : : : : : : : : |
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Thanks Edd
I will try to get to your suggestions on sunday.
I aligned the IF to 460kc beacuse that is what the paperwork says. Was 470 a typo or is it really supposed to be that. I adjusted untill maximum amplitude on scope was reached. There is -dc on the grid but I am unsure how much. It is NOT totally unresponsive, it still moves very slightly 1-5 degrees when on a stong station or passing over one.
Thanks
Ian
::
:: :: :: :: :: :: :: ::Sir Ian . . . . . :: :: ::Ohhhhh Tayyyy . . . I started on this reply days ago but just now found time for its completion, ::and some of its points have been lightly touched upon since its initiation, so I am just going let it ::all rip, in its entirity. :: :: ::Indeed that set of yours was quite state of the art at its early time period with all of its features, ::with some particular note to its dedicated and separate AVC system. :: :: ::What I might note initially, was your comment as to the eye tube "working" on day one, but not ::confirming, as in remembering for sure, if it closed completely on strong stations. :: :: ::If so, I also think of some fault concerning circuit work, since that time, created the present problem. :: ::Specifically, the creation of adequate sound from the set is not inclusive of having good /high enough gain thru the RF and IF system so as to ensure a healthy DC level output from the detector stage(s). :: :: ::AND that degree of detected DC voltage level is that which is used to feed to the eye tube circuitry. :: :: ::Reference the Marked- Up Schema: :: :: :: ::Take note of the detector section marked up in [AQUA] at reference [ F ] there is the AUDIO content ::which zips on up to the 6C5 audio stage and the DC componemt present is hi Z isolated a bit with the ::R-20 . . .2.2 meg and its .01 ufd , which adds a bit of hang time to changes made while tuning in to a station. :: :: ::That negative voltage level changes the degree of response of your eye tubes pattern. STRONG signal ::from the station, more negative voltage developed and more response from your eye tube. :: :: ::This might now be a good time to give JUST the eye tube circuitry an evaluation. :: :: ::(And you do have a 1 meg resistance unit in the eye tube socket . . plate to target . . . right ? ) :: :: ::I usually suggest that one gets a 9V battery and connect across a 1 meg pots outer terminals and then ::run a 1 K "stopper" resistor off from that pots center /rotor terminal. :: :: ::That then gives one a variable source of negative voltage as referenced between the + terminal of the ::battery and that outer connection of the 1K limiter resistor. :: :: ::HOWEVER, in your situation you have a "fresh" source of negative voltage present DOWN / bottom/left at the power supply at the [YELLOW] - [V] reference. :: :: ::What say we now lift the 2.2 meg resisitor R20 from its [AQUA] reference [ F ] connection and then take a clip lead and connect the floating 2.2 meg to that negative voltage source at - [V] and fire up the set and see what degree of ::response the eye tube is now providing. :: :: ::If now responding, far better than initially, we just now have to back track to the simple [ F ] source of the eye tubes negative sensing voltage and take a negative voltage measurement to see exactly what DC level IS being present on that supply point. :: :: ::Look for your very strongest stations, as the maximum voltage at [ F ] will be present on those same stations, then compare that max voltage to what you are reading at the -V supply, that will be the difference that the voltage from the detector will have to be increased to, in order to get the like response of the eye tube. :: :: ::( Out in left field question . . was any alignment done to the receiver ? Particularly the IF stages . . .or any remote chance the unit was aligned to 455/6 instead of 470 ?) :: :: ::O.K. then . . . the next analysis step would be monitoring of [ F ] for its neg voltage level and tune in too ::the STRONGEST station that you can receive, and then make a duo directional micro movement (1/4 turn ? )of the 6 separate trimmer caps of the 1st/2nd/3rd IF transformers to see if that -voltage level can be brought up any higher. ::Leave each at the peak voltage output . :: :: ::Did that bring up your available detected voltage up closer to that prior ascertained requirement of the eye ::tube ? :: :: ::If not, then lets look at another aspect of the receiver, its quite refined AVC system: :: :: ::That circuitry signal flow has been highlighted in [ BLUE ] and [ GREEN ] on the schema referencing. :: :: ::On examining of the 1st grid circuitry of the 2nd IF stage, we see a sampling of the moderately high level of ::470 IF signal by the [BLUE ] line which goes down to C66 to be coupled into the the dedicated IF stage amp. :: :: ::This stage is running at full gain , and not being held back, as the upper 2nd IF stage is, with its reduced ::screen voltage. The sharpness of IF tuning has already been established by the multiple stages of the main ::IF 's, so this RF stage is broad tuned with no concern given to its tuning. :: :: ::Signal flow is being designated by the blue squares path. :: :: ::After detection by the AVC 6H6, the AVC control voltage is dumping into load resistor R37 and having a bit higher level present across a 150, 000 load vice the typical 47K, then the flow down to the R36 and its .O5 summing capacitor, which gives a bit longer decay time for the AVC system, than was present back on the eye tubes supply at [F]. :: :: ::The resultant AVC flow is down the [GREEN] busses and their individual isolation resistors and EACH associative decoupling capacitor, with a whole BUNCH of them being present on that AVC buss with NONE of them wanting to be exhibiting ANY leakage to ground. Or elso you can just kiss your system AVC's dynamic range swing . . . goodbye. :: :: :: ::This time we are are interested in a gradual decrease of the gain of the RF stages, with that being stretched a ::bit more with those stages also having further resistive isolation and their .05 capacitors associated with ::them. :: :: ::What I might ask you to try now is to monitor [BLACK] # 1 reference, for that detected AVC DC voltage and ::see how negative it is, as compared to the equivalent [ F ] test point we just measured earlier? :: :: :: ::ASIDE: * * * :: :: :: ::If it is being appreciably higher , whip thru the stations on the dial and leave it tuned in to the strongest station. :: :: ::Then, I think that you still have the R20 2.2 meg resistor end available for us, so take a clip lead and jumper ::between it and the [BLACK] # 1 AVC source to now see how the eye tubes responds using your AVC voltage ::as its drive. :: :: ::One final thought, on these tests, if the original eye tube driving voltage never came up at ref [ F ], I now hope that you are equally ::knowledgeable / stocked in cross technology apart from these "old radios" and also happen to have a 1N4148 / 1N914 diode available in your parts cache to shunt across the "top" 6H6 such that its anode goes to the plate connection and its cathode goes to ground. Then, see what the detected voltage level hops up to. :: :: ::( If having none of those above diodes, even a "slow" common 1N4001-thru- 4007 "power" diode would do in this pinch. ) :: :: :: :: :: :: ::ASIDE: * * * :: :: ::[ BTW back to the use of two 6H6, for plain 1/2 W detection circuitry on BOTH units with unused elements grounded . . . no exotica involved, such as voltage doubling. :: :: ::As for not cross sharing of a 6H6 diode for EACH circuit, I suspicion the detrimental effect of intra stage cross wiring spread out and potential feedback effects from the capacitance proximity in doing that. ) :: :: :: :: :: :: :: :: ::Standing by for exploratory updating . . . or ?'s. :: :: :: :: :: :: :: :: :: ::73's de Edd :: :: :: :: |
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:: :: :: ::RCA Mark-UP . . . . . . Working SCHEMATIC: :: :: :: :: :: :: :: :: :: :: |
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:Thanks Edd
:I will try to get to your suggestions on sunday.
:I aligned the IF to 460kc beacuse that is what the paperwork says. Was 470 a typo or is it really supposed to be that. I adjusted untill maximum amplitude on scope was reached. There is -dc on the grid but I am unsure how much. It is NOT totally unresponsive, it still moves very slightly 1-5 degrees when on a stong station or passing over one.
:Thanks
:Ian
That was my undetected typing error, just aside on one keystroke, of course, 460 is correct.
73's de Edd
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The - voltage on the eye grid was -.5v
I began changing the if's the 3rd coild secondary was all the way tight. After I loosened it half way the voltage came up to ~6 eye works great. When I was using the scope to read the voltage, this winding had little to no affect on the audio/voltage on scope.
I put it back together just now, and it sounds great. it has more bass than any other radio I have fixed so far. It sounds like it has a subwoofer almost.
Thanks so much ( I guess that the eye did work before......)
Next project-Sparton 1568 (already recapped-untested)
Ian
T.
I did this multiple times (probably where I messed up)
The paper work recomends a scope, generator, frequency modulator... ALL RCA factory equpment.
What really matters is it works now. It looks great, plays better. When recapping I made a mistake, the two tone caps (tar packed) were .5mfd. Initially i repalced them with .05 (much more reasonable). However, I did put the .5's in. It really needed them. I cant even tell that it is coming from a radio, sounds better than my amp. After that last if coil was reajusted the bass exploded.
I strongly recomend this model to anyone who has the space.
Thanks again
Ian
:When aligning the IF transformers, us the lowest signal generator output possible. Perhaps the reason why the 3rd IF had no affect on voltage is because by the time you aligned the other stages, so much signal was getting through that the AVC circuit was kicking in, nullifying any further signal strength changes. When you align one transformer, reduce the signal generator output as low as possible and align it again. Reduce output again and proceed to the next stage. Repeat. Once all stages are aligned, repeat again, though if you continually reduced generator output for each stage and then went back and realigned it, it shouldn't need realigning later.
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:T.
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T.
Ian
T.
I had a similar problem with a Clinton AA5 several years ago. I recapped the entire set - replaced out-of-tolerance resistors, etc.....still, the eye worked properly only on the very strongest stations. It was when I took the schematic and traced out ALL the circuitry that I found the problem. Someone had made a couple of subtle wiring changes over the years - the work was very neat and hard to detect by sight alone. When the proper connections were restored - the radio (& eye tube) worked flawlessly. Take a copy of the schematic and a hiliter - and trace out all the circuitry (double check values / test all components along the way)......