Sparton 1568 Alignment

2/19/2010 2:37:32 AMIan

Hi, Im working on my Sparton 1568
http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf

IT works grea, except the lower frequency am won't work well.
During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
WJR barely comes in, where as a station at 1200 is booming.
Im going to test some voltages and keep trying, I will be awake for some time yet.
Ian

2/19/2010 11:16:02 AMNorm Leal

Hi Ian

This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.

Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.

Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.

Norm

:Hi, Im working on my Sparton 1568
:http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
:
:IT works grea, except the lower frequency am won't work well.
:During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
:WJR barely comes in, where as a station at 1200 is booming.
:Im going to test some voltages and keep trying, I will be awake for some time yet.
:Ian
:

2/19/2010 4:12:56 PMIan

When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
Ian

:Hi Ian
:
: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
:
: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
:
: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
:
:Norm
:
::Hi, Im working on my Sparton 1568
::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
::
::IT works grea, except the lower frequency am won't work well.
::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
::WJR barely comes in, where as a station at 1200 is booming.
::Im going to test some voltages and keep trying, I will be awake for some time yet.
::Ian
::
:

2/19/2010 8:46:10 PMNorm Leal

Hi Ian

Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.

Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.

Norm

:When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
:The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
:Ian
:
::Hi Ian
::
:: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
::
:: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
::
:: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
::
::Norm
::
:::Hi, Im working on my Sparton 1568
:::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
:::
:::IT works grea, except the lower frequency am won't work well.
:::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
:::WJR barely comes in, where as a station at 1200 is booming.
:::Im going to test some voltages and keep trying, I will be awake for some time yet.
:::Ian
:::
::
:

2/21/2010 5:19:08 AMIan

I think somthing is very wrong.
Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
I checked all resistors and replaced most.
B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
Help! Please!

:Hi Ian
:
: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
:
: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
:
:Norm
:
::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
::Ian
::
:::Hi Ian
:::
::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
:::
::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
:::
::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
:::
:::Norm
:::
::::Hi, Im working on my Sparton 1568
::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
::::
::::IT works grea, except the lower frequency am won't work well.
::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
::::WJR barely comes in, where as a station at 1200 is booming.
::::Im going to test some voltages and keep trying, I will be awake for some time yet.
::::Ian
::::
:::
::
:

2/26/2010 9:01:48 PMIan

Bump
Any ideas anyone?

:I think somthing is very wrong.
:Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
:I checked all resistors and replaced most.
:B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
:Help! Please!
:
:
::Hi Ian
::
:: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
::
:: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
::
::Norm
::
:::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
:::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
:::Ian
:::
::::Hi Ian
::::
:::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
::::
:::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
::::
:::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
::::
::::Norm
::::
:::::Hi, Im working on my Sparton 1568
:::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
:::::
:::::IT works grea, except the lower frequency am won't work well.
:::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
:::::WJR barely comes in, where as a station at 1200 is booming.
:::::Im going to test some voltages and keep trying, I will be awake for some time yet.
:::::Ian
:::::
::::
:::
::
:

2/26/2010 9:57:05 PMNorm Leal

Ian

When a radio only receives a strong station the oscillator may not be operating? In that case a tuner will act somewhat as a volume control. Instead of changing stations it will have an effect on volume.

Bring your hand near the 6A8 and increase volume indicates antenna coil is open of stage not peaked up. Your hand is acting as an antenna. Do you have an antenna connected to the radio?

Norm

:Bump
:Any ideas anyone?
:
::I think somthing is very wrong.
::Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
::I checked all resistors and replaced most.
::B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
::Help! Please!
::
::
:::Hi Ian
:::
::: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
:::
::: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
:::
:::Norm
:::
::::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
::::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
::::Ian
::::
:::::Hi Ian
:::::
::::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
:::::
::::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
:::::
::::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
:::::
:::::Norm
:::::
::::::Hi, Im working on my Sparton 1568
::::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
::::::
::::::IT works grea, except the lower frequency am won't work well.
::::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
::::::WJR barely comes in, where as a station at 1200 is booming.
::::::Im going to test some voltages and keep trying, I will be awake for some time yet.
::::::Ian
::::::
:::::
::::
:::
::
:

2/26/2010 10:08:17 PMIan

I have an antenna attached to the radio when not aligning it because the siggenerator goes to antenna post. I Will check for an open coil.

:Ian
:
: When a radio only receives a strong station the oscillator may not be operating? In that case a tuner will act somewhat as a volume control. Instead of changing stations it will have an effect on volume.
:
: Bring your hand near the 6A8 and increase volume indicates antenna coil is open of stage not peaked up. Your hand is acting as an antenna. Do you have an antenna connected to the radio?
:
:Norm
:
:
::Bump
::Any ideas anyone?
::
:::I think somthing is very wrong.
:::Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
:::I checked all resistors and replaced most.
:::B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
:::Help! Please!
:::
:::
::::Hi Ian
::::
:::: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
::::
:::: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
::::
::::Norm
::::
:::::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
:::::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
:::::Ian
:::::
::::::Hi Ian
::::::
:::::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
::::::
:::::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
::::::
:::::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
::::::
::::::Norm
::::::
:::::::Hi, Im working on my Sparton 1568
:::::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
:::::::
:::::::IT works grea, except the lower frequency am won't work well.
:::::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
:::::::WJR barely comes in, where as a station at 1200 is booming.
:::::::Im going to test some voltages and keep trying, I will be awake for some time yet.
:::::::Ian
:::::::
::::::
:::::
::::
:::
::
:

2/26/2010 11:14:11 PMIan

I feel really dumb right now.
The jumper between the G and D position fell out
Put it back, and it gets MANY stations, wjr came in at over 6 volts.
Now, the audio isnt the best scratchy and treble is a little low.. will work on it, and I still cant get one local station WPON 1460

:I have an antenna attached to the radio when not aligning it because the siggenerator goes to antenna post. I Will check for an open coil.
:
::Ian
::
:: When a radio only receives a strong station the oscillator may not be operating? In that case a tuner will act somewhat as a volume control. Instead of changing stations it will have an effect on volume.
::
:: Bring your hand near the 6A8 and increase volume indicates antenna coil is open of stage not peaked up. Your hand is acting as an antenna. Do you have an antenna connected to the radio?
::
::Norm
::
::
:::Bump
:::Any ideas anyone?
:::
::::I think somthing is very wrong.
::::Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
::::I checked all resistors and replaced most.
::::B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
::::Help! Please!
::::
::::
:::::Hi Ian
:::::
::::: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
:::::
::::: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
:::::
:::::Norm
:::::
::::::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
::::::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
::::::Ian
::::::
:::::::Hi Ian
:::::::
::::::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
:::::::
::::::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
:::::::
::::::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
:::::::
:::::::Norm
:::::::
::::::::Hi, Im working on my Sparton 1568
::::::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
::::::::
::::::::IT works grea, except the lower frequency am won't work well.
::::::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
::::::::WJR barely comes in, where as a station at 1200 is booming.
::::::::Im going to test some voltages and keep trying, I will be awake for some time yet.
::::::::Ian
::::::::
:::::::
::::::
:::::
::::
:::
::
:

2/27/2010 11:47:59 AMNorm Leal

Ian

Glad you found it.. 1460 is near top end of the dial. Use trimmers to peak up this end. Trimmers have the most effect at high end of a dial.

Norm

:I feel really dumb right now.
:The jumper between the G and D position fell out
:Put it back, and it gets MANY stations, wjr came in at over 6 volts.
:Now, the audio isnt the best scratchy and treble is a little low.. will work on it, and I still cant get one local station WPON 1460
:
::I have an antenna attached to the radio when not aligning it because the siggenerator goes to antenna post. I Will check for an open coil.
::
:::Ian
:::
::: When a radio only receives a strong station the oscillator may not be operating? In that case a tuner will act somewhat as a volume control. Instead of changing stations it will have an effect on volume.
:::
::: Bring your hand near the 6A8 and increase volume indicates antenna coil is open of stage not peaked up. Your hand is acting as an antenna. Do you have an antenna connected to the radio?
:::
:::Norm
:::
:::
::::Bump
::::Any ideas anyone?
::::
:::::I think somthing is very wrong.
:::::Now the only station I can get is my own transmitter, and the generator. I think that the problem is the osccilator because every few minutes I have to retune the radio to my transmitter. IF output voltage is ~5 @ 1500, and .5 @ 600. When I put a screwdriver (one in paticular works better than the rest) the voltage goes up to 3.8. When I move my hand close to the RF or 6a8 tubes volume goes up. I have tried many tubes, and differnt types (metal, gt, g) no difference. Radio still recieves my transmitter faintly without the RF in the radio.
:::::I checked all resistors and replaced most.
:::::B+ came down a bit, so I removed the 1000 ohm wirewound, B+ is now ~425v (400 on paper)
:::::Help! Please!
:::::
:::::
::::::Hi Ian
::::::
:::::: Don't use the padder to peak this voltage. Tune to the lowest station you receive and adjust padder for max volume while rocking tuning back and forth. The signal will come up.
::::::
:::::: Wire wound or carbon resistors won't be a problem on the B+ line. You don't have to worry about inductance as there will be caps to ground on both sides of a resistor.
::::::
::::::Norm
::::::
:::::::When the padder C11 is screwed trightly the voltage goes up to about half of what the high end (1500) yields. I get NO staions below 1000 except WJR , but it is very faint. The eye tube doesnt move on lower stations , including the signal from the generator,
:::::::The B+ was very high, I dropped it down with a large resistor, the bass decreased dramatically. Is this becasuse it is a wirewound resistor?
:::::::Ian
:::::::
::::::::Hi Ian
::::::::
:::::::: This radio has padder caps identified as C11, 12 and 13. These adjustments are used to peak up the low end of bands.
::::::::
:::::::: Adjust the padder while rocking tuning back and forth, listening to low end of the dial. Set for the loudest signal.
::::::::
:::::::: Oscillator voltage will change as you tune across the dial. This is normal and won't have an effect on operatrion as long as the osc keeps operating.
::::::::
::::::::Norm
::::::::
:::::::::Hi, Im working on my Sparton 1568
:::::::::http://www.nostalgiaair.org/PagesByModel/687/M0018687.pdf
:::::::::
:::::::::IT works grea, except the lower frequency am won't work well.
:::::::::During alignment @ 1500 There is -5 dc at the junction of c37, L12, and r17. When aligning lower end (600) it reads ~1.7 volts. I can get it to decrease but not increase. When the screwdriver is on the trimmer screw of the padder, The voltage goes up to over 2.5 volts. I noticed that this trimmer is Physically backwards to all of the others, could this do it?
:::::::::WJR barely comes in, where as a station at 1200 is booming.
:::::::::Im going to test some voltages and keep trying, I will be awake for some time yet.
:::::::::Ian
:::::::::
::::::::
:::::::
::::::
:::::
::::
:::
::
:

3/6/2010 1:56:57 AMIan

It works ok. Eye tube closes completely on my transmitter, and partially on wjr. Gets many stations with no movement. Sound quality is excellent. Voltages normal except one. Pin 6 of the 6c5 is supposed to have 20v it has 1-5v on it. ALL resistors have been checked or replaced. When the off/afc/afc+expander switch is switched from off to afc, there is a loud pop, and a decrease in volume, but no change in signal strength. When switched to expander, signal voltage drops, volume drops, and eye tube opens more (can retune to get back to same %closed but with less volume) AFC doesn’t help at all, makes quieter. I have no experience with the AFC/expander/discriminator circuit. Please help someone
Thanks Norm for the previous help.
Ian

3/11/2010 7:17:08 PMHelp Please

:It works ok. Eye tube closes completely on my transmitter, and partially on wjr. Gets many stations with no movement. Sound quality is excellent. Voltages normal except one. Pin 6 of the 6c5 is supposed to have 20v it has 1-5v on it. ALL resistors have been checked or replaced. When the off/afc/afc+expander switch is switched from off to afc, there is a loud pop, and a decrease in volume, but no change in signal strength. When switched to expander, signal voltage drops, volume drops, and eye tube opens more (can retune to get back to same %closed but with less volume) AFC doesn’t help at all, makes quieter. I have no experience with the AFC/expander/discriminator circuit. Please help someone
:Thanks Norm for the previous help.
:Ian
:
:

3/13/2010 5:57:50 PMEdd

Sir Ian. . . . . .

Help Please . . . .

Now, would that be as in . . . . . Help, Help, Me Rhonda . . . . a la Beach Boys ????

In referencing to some of your different comments and queries:

I noticed that this trimmer is physically backwards to all of the others

I feel really dumb right now. The jumper between the G and D position fell out

It works ok. Eye tube closes completely on my transmitter, and partially on wjr.

Gets many stations with no movement. Sound quality is excellent.

Lets's start off with your current question on the AFC circuitry, as is being used on the BC band:

That set of your was quite ahead in some features and design for its time frame.

Now you are wondering about aspects of its AFC feature, providing for a capability of keeping the set tuned right on frequency with time, as well as providing a slight correction, just in case 'ole Granny Goodknockers or Delmer "Deft-fingers" Dummnuttz did not get tuned quite exactly onto a station initially.

That miss tuned condition slightly enhancing treble, but being a bit detrimental due to its bass decreasing effect.

* * * * * The sets AFC circuitry:* * * * *

I have provided a markup schema, at extreme bottom, of the involved circuitry, as well as now giving a circuit flow run down of cause and effects.

Your initial point of interest will be all of the [ YELLOW ] highlighted area of the Discriminator circuitry at the top right location on the schema .

A sample of 455/6 Khz I.F. signal is taken from the plate of the second IF amp, via C35 sampling capacitor. With 50 mmf being their choice for getting the desired amount of RF level that they wanted.

With less capacitance providing lower RF feed thru. . more capacitance more RF feed thru . . that, of course, being a function of the capacitance reactance exhibited at the frequency involved.

This RF sample then gets connected to the center tap of the AFC winding, as is being seen over at the far right side of L12. It also is feeding down to a balanced set of load resistors R15/16.

Each discriminator coil outer winding end gets connected to a respective plate of the 6H6 tube. They will then be receiving an I.F. signal that is a combination of the sampled RF going into the disc windings center tap and the induced voltage by virtue of the close proximity of the L12 IF primary plate winding of the transformer.

The whole AFC secondary is tuned to a 455/6 frequency setting with its coil and its C36 fixed capacitor and its shunting C39B trimmer capacitor. The bulk of the tuning coming with the C36 value and the "fine tuning" is being done with C39B’s final capacitive value setting.

If there is a tuning error present up at the front end tuning condenser setting, in respect to its not being set right ON to the station, the detected voltage up at pin 4 of the 6H6 will shift in level and polarity with the direction of tuning error.

That voltage gets filtered and RF stripped to result in a DC level with C40 assistance and that voltage then flows to the left thru isolation/dropping resistor R14 to then enter into the [ GREY ] marked-up buss and its eventual flow downwards to the point where you see it either branching to the bottom to pass through S8 which, if it is switched into the proper mode, to then pass the voltage on down to S10.

If that S10 switch is open, as it is now shown, there will be AFC action possible. HOWEVER, if it is closed, the AFC corrective voltage buss gets shorted out to ground and there is no corrective AFC action possible when switched to that position.

Now, considering that S10 AFC switch is being open, and therefore being in its AFC active position, go back up to the [ GREY ] buss where it then branches out.

Now observe the [ GREY -DOT ] mark up path flowing to the LEFT, a bit further over you will then see one more voltage dropping/isolative resistor . . . R6 . . . before the buss flows down to the control grid of the 6J7 tube.

That slight voltage level presence of a tuning error control voltage being presented to the 1st grid of the 6J7 control tube will make a slight change in the plate characteristics of the 6J7 tube, which has its plate connected [ PURPLE BUSS routing ] to a tap on the BC osc coil L7.

Therefore, it will then be causing a slightly corrective skewing of the local oscillator frequency to shift the osc frequency of the set into being correctively tuned right onto that station.

While the local oscillator is gradually / initially skewing its frequency, back at the discriminator there is a declining level of that corrective voltage then being sent to the oscillator until the oscillator is finally left lock tuned onto the proper frequency.

* * * * * The sets AVC circuitry:* * * * *

The only other point of interest might be the AVC system of this set, and since it is using an RF amplifier at the front end, and two mind you TWO . . . IF stages, the set is just bristling with gain. A gain that needs to be controlled, and they are incorporating what I refer to as a “brute strength" AVC derivation technique.

If this was just the typical plain vanilla AVC circuit, look just below the L12 2nd IF transformer and the white area , where one sees the top of the secondary winding of the IF transformer feeding down to a diode detector plate of the 6Q7 below.

The other winding end of the secondary is dumping into R17 load resistor and then the high side of that R17 feeds to the left to a C-R-C pi-network filter that initially strips off any 455/6 residual RF and the higher ultrasonic AF frequencies present with the detected audio signal.

That combined negative DC and AF signal ends up where the phono normally gets tied in, at the very top of the [RED X ] markup.

NOW if this was the typical AVC configuration experienced, that top [RED X ] area would be the tap in point where the negative voltage DC component present, would then be flowing thru a couple of dropping/isolation resistors and bypass condensers to ground to establish the engagement and decay characteristics of the whole AVC system.
Then that control voltage is being further distributed to the 1st grid, cold end, of tuned circuitry associative with the frontal RF stage and I.F. stage(s) of the set to establish their stage gains.

Progressively lower gain being required on stronger received stations, with minimal control of gain being needed for the optimal reception of the weaker stations.

This sets AVC design:

NOW . . . the way that they do it on this set is shown at the [ AQUA ] buss where the bristling high level of IF signal at the plate of the is tapped off with a 50 mmf capacitor with the small I.F. RF level flowing down to #4 of the 6Q7 where all of the + nodes of the signal get conducted off, with only the negative signal nodes transitioned to a negative DC level, with the accumulating assistance of C21 [ YELLOW MARK-UP ] on that buss up, schematically located up under the sets RF amp tube.

En toto . . .The AVC [GREEN ] buss has its origin by branching off from the [AQUA ] buss and starts its flow to the left and intercepts an isolation / dropping resistor as R8 and then the flow of AVC control voltage [ GREEN -DOT ] up to 1st grid circuitry of the 1st IF amp.

Drop further down the green buss and from that reference point and you will see its feed to the control grid of your VISOGLO eye tube grid and then the [GREEN ] buss continues to the left and you see it feeding up to provide gain control of the frontal RF amp[ GREEN -DOT ] path, with the companion C18 aforementioned cap tied into this buss to establish the attack/decay characteristics of the AVC voltage on this buss.

There is yet another AVC BUSS tie in at R1 to feed to the mixer grid of the 6A8 converter circuitry [ GREEN -DOT ] route, with a bit more filtering via C21 to preclude any "FM'ing" of the stage.

* * * * * This sets expander circuitry:* * * * *

You commented on a plate voltage error on the 6R7 /6C5 tubes circuitry and that is probably not in error, as it will have some degree of variance as the controls and switching in that area are shifted.

Initially notice that your sets volume control is basically using the R19A volume control off to the top left of the 6Q7 1st audio amp tube.

It is carrying in the desired level of audio into the 1st grid of the 6Q7 tube. The audio is amplified in that stage and taken off from the plate and initially the very HF AF . . impinging upon ultrasonic . . high frequency is being bypassed off to ground by C43.

Then the initial AF signal flow is made down from that plate and in thru the small dog leg of the [PEA GREEN] highlighted area, The signal flow is then down thru the [CERISE] mark-up and thru the multiple R-C components to then finally emerge down at the bottom of that dog leg and provide the altered audio to the 1st grid circuitry of the 6J5 2nd audio / driver stage.

Now this is the aspect where your sets audio really shines . . . as on ole' Joe Blows’ radio . . he was in real tall cotton if his little set even had the DEEEE-LUXE feature of a switched in capacitor or capacitor /variable resistance Tone Control feature being added onto his set.

And, if having the right brand / design, he might also even have had a loudness compensation feature, whereupon there is a tap on the volume control off from its lower volume range position to tie in to a small capacitance AF bypassing condenser to ground.

That variable bypassing, in accordance to the volume pots rotor position, would initially heavily bypass the treble frequencies, making the old ear think that there actually was more bass presence when being used at lower volume levels.

As the volume was increased, the treble damping then decreased proportionally, since the volume was coming up and the old ears response was kicking in and starting to perceive low frequencies more readily now.

As the volume is brought up even more, the point is met where the volume controls rotor is coincident with the established tap off point and its further rotation then disassociates the compensation filtering, since the rotor is then up mechanically and electrically PAST that tap off point.

NOW . . . your sets circuitry is using a much enhanced, and even AMPLIFIED variance by your initiall seeing that the sets volume control R19A , also has a piggy backed R19 B which will be tracking the volume control movement with providing stage gain control of the 6R7 by a tracking with R19B's resistance shifting.

Look at the top half of the [CERISE] mark-up and over to the left of the adjunct [PEA GREEN] highlighted area and note those R/C filtering networks that get fed over to the EXPANDER input circuitry and eventually get returned as a gain controlled--tone shifted reintroduction into that lower [CERISE] circuit path of the 1st/2nd audio stage inter coupling.

There is even an enhanced tone control circuit employing . . .T1 (inductor) plus C shaping elements . . . instead of the common use of simpler/typical R/C elements .

This set’s circuit methodology is one great step up from the ordinary loudness compensation circuitry that is being used to compensate for the Fletcher- Munson response curve of our hearing at lower volume levels of listening to the set.

Another aspect of a query was per the difference in the physical aspects of the osc adjustment padders for the three bands of the set. ( Referencing back to your)

I noticed that this trimmer is physically backwards to all of the others

Those sets I have marked up in [ PALE ORANGE ]. They are composed as pairs, with the fixed value capacitor providing the most of the capacitive tuning value, with the adjustable companion unit, merely providing the vernier adjustment of the "C" value.

In the case of the C13 SW band and C12 PO-LEEECE-US-ES-ES band, note that one terminal end results in its getting connected to ground. BUT that C11 capacitor ends up being within a series connected arrangement . . .not going directly to ground . . .Sooooo, on that element pair . . . .that is probably the different mechanical configuring that you were seeing.

Also, on those compression mica type of variable units, it is common to have the adjustment screw insulated from the top leaf of the capacitor, OR ELSE, if that slotted binder head adjstment screw IS making direct contact with the top leaf, that leaf connection should be the particular one dedicated to going to ground. Thereby use of a metallic bladed screwdriver does not detune the circuitry.

In your case of the C11 adjustent, floating like it is, one should be using a non metallic insulated screwdriver for that particular adjustment.

In my findings, those tools are not mechanically tough enough and chip or shred up the end.

To counter against that, I have used a Hard Plastic / Delrin / Fiberglass /or / Nylon 1/4 inch rod and used a thin . .Dremel #409 cut off wheel to make a 1/8 inch deep slot across both ends and inserted separate 1/4 by 1/4 square inserts cut from a hacksaw blade (also using a Dremel tool). That insert is then epoxied in place and that ends up with a metal reinforced end that will hold up to torque demands.

The capacitance shift of that small amount of metal presence is insignificant but, stress mechanical enhancement is priceless.

* * * * * AFC adjustment for the set:* * * * *

And now . . . .drum roll . . . the adjustment of that AFC feature used on the BCB.

Initially check out the S10 switch schematically located at the bottom left of the [PEA GREEN] highlighted area and mechanically located on your set . . . I know not where . . . position wise.? It could even be associated with a push- pull action of the tuning knob shaft or some of the electro- mechanics of the auto tune feature.

The easiest way to find out for sure is to hang one ohmmeter on the high terminal of S10 and the other ohmmeter lead to ground and find the one OR combination of multiple switch manipulations on the unit that results in that terminal ended up being grounded .

I suspect S10 itself and also one other Switch, being interconnected thru a band switch function, if the set is placed off from BCB position.

Sooooo you figure it out, by finally having the set operating on BCB mode and without that S10 junction ending up being grounded.

The next aspect for consideration is for the unit to be aligned to 455/6 Khz or be working good enough for you to give it credit as being close enough in alignment by its good performance and sensitivity already. Which you seem to sort of already imply, by the glowing performance reports and overall audio quality.

As per the top of page

It works ok. Eye tube closes completely on my transmitter, and partially on wjr.

Gets many stations with no movement. Sound quality is excellent.

INSERT:

I feel really dumb right now. The jumper between the G and D position fell out

(You certainly lucked out in finding that SELF IMPOSED "link/jumper . . . problem", associated with the BCB circuitry, back in the exploration of a potential "padder misalignment" . We just can't fathom out some odd ball problem like that, which normally is NOT something we are finding as a recurring fault within sets.

Later in time, I will make a general write up on Tracking as a separate stand alone topic which then permits SEARCH mode method for using as a FAQ reference, instead of being lost way y y y down within a thread that is further branched off from a topic. )

RESUMING:

Now, with the set warmed up, you unplug the 6H6 detector tube and tune in precisely to an AM BCB station. Place DC voltage mode meter monitoring from the [ GREY ] AFC correction buss with the other meter lead being referenced to ground terminal.

Jot down that voltage value.

Then you plug in the 6H6, warmup, and take another reading of that voltage value then being present, a variance would be indicative of an attempt of the AFC circuitry trying to make a tuning correction.

BUT, from what you describe as to having experienced , it is making it in an INCORRECT direction, due to a mis alignment of the Discriminator secondary.

What SHOULD be happening now is that this developed corrective AFC voltage will be going down to the reactance control tube to be adding to or subtracting from an already present quiescent voltage.

That AFC feedback voltages action, if of the proper level and polarity, should cause the reactor control tube to skew the oscillator tuning in the proper corrective tuning direction, and with getting closer to being in tune the voltage level will decrease until there is progressively less correction being provided until locked in tune to the station.

Now the three conditions that we might expect to experience is that the discriminator secondary tuning winding is not tuned to 455/6 Khz or being a bit below or below that 455/6 tuning. Thus, an error correction voltage is being sent to the control tube.

What we need to do is ever so slightly shift the tuning of the discriminator secondary trimmer to see which direction its adjustment is presently in error.

This is where we might need a few feed backs to confirm BUT initially lets work on the concept that you initially pick a radio signal of such strength that you are able to get a full swing of the tuning eye when it is being tuned in to.

Too strong of a station and the swamping signal might hold the tuning eye closed most of the time. I would think that a station with a signal level that almost half closes the tuning eye would give us the most meaningful utilization of the display.

Soooo . . . you now go back to measuring the AFC correction voltage on the [ GREY ] buss . . your control tube should have made a correction to the BCB local oscillator with this control voltage, but NOT towards having thrown it further out of tune instead.

Observe the tuning eye to see in which direction of the slight initial adjustment of the DISCRIMINATOR transformer windings companion C39B trimmer capacitor will be bringing on a more fully closed condition of the tuning eye.

In one direction it should decrease closure and the other direction it should more fully close. Leave it set at the optimal received signal strength condition.

That should have your AFC circuitry properly correcting.

You could now verify its proper tracking action by jumper clip shorting out S10 switch to disable the AFC corrective feedback voltage and then manually use the sets main tuning condenser to be then tuned just a smidge off on the low frequency side, as from being tuned right onto the station.

Release the S10 short and the AFC correction should shift and hold to an on station tuning condition.

Repeat the same procedure above, but, by slightly tuning off from the station on the high frequency side this trial.

* * * * * Stopping at this point for feedback or queries . . . if any . . . .* * * * *

73's de Edd

Ye Olde Spartacus 1568 Chassis Mark-Up Schematique:

::It works ok. Eye tube closes completely on my transmitter, and partially on wjr. Gets many stations with no movement. Sound quality is excellent. Voltages normal except one. Pin 6 of the 6c5 is supposed to have 20v it has 1-5v on it. ALL resistors have been checked or replaced. When the off/afc/afc+expander switch is switched from off to afc, there is a loud pop, and a decrease in volume, but no change in signal strength. When switched to expander, signal voltage drops, volume drops, and eye tube opens more (can retune to get back to same %closed but with less volume) AFC doesn’t help at all, makes quieter. I have no experience with the AFC/expander/discriminator circuit. Please help someone
::Thanks Norm for the previous help.
::Ian
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