I have a Zenith console 10S668 with a 10-B-1 chassis.
Even with the volume turned all the way down, the volume is fairly high.
I can short the center tap of the volume control to ground, and it makes little difference.
However, if I ground the grid of the 6J5G Inverter, the volume is OK.
I noticed the resistors R20 and R21 across the 6V6 Grids are listed as 330 M and 47 M Ohm.
The ones in my circuit are 330K and 47K.
A misprint? Or someone replaced with wrong value?
Any other suggestions?
Dennis

330k and 47k are the correct values. During that time the roman numeral M was used for 1000 or kilaohms

:I have a Zenith console 10S668 with a 10-B-1 chassis.
:Even with the volume turned all the way down, the volume is fairly high.
: I can short the center tap of the volume control to ground, and it makes little difference.
: However, if I ground the grid of the 6J5G Inverter, the volume is OK.
: I noticed the resistors R20 and R21 across the 6V6 Grids are listed as 330 M and 47 M Ohm.
: The ones in my circuit are 330K and 47K.
:A misprint? Or someone replaced with wrong value?
:Any other suggestions?
:Dennis
:

What "center tap" are you grounding? If this is the tap all by itself, then it will make little difference. The terminal right between the other two terminals should make a difference. Try grounding this. There are likely two reasons as to why your control is not working properly. One is that a connection to the low terminal is faulty either at the control or somewhere else. The low terminal is the one of the three that are close together that is to your left, with the three terminals facing down and the shaft facing you. This terminal is connected to ground or something else at a similar potential. I looked at several diagrams listed here. Yours is not listed (10-S-668). In the diagrams I saw, some had the low end of the volume control connected to the center tap of the power transformer high voltage supply, and some had it connected to a resistive network afterward. Simply follow the wire from this terminal within your radio and check all places that it is connected to.

The other possible problem (probably more likely than the first problem) could be that the conrol is damaged itself. This could be caused by the resistive material being worn out at the low end of the control, which is very possible since this part of the control gets used the most (every time you turn off the receiver, and when you are listening to programs at anything other than a blaring level). It could also be caused by the control being cracked at this point or the terminal being loose on the control. To test for this, disconnect the low end terminal wire from this terminal. Connect your multi-meter with one wire to this terminal and one wire to the center terminal--the one right next to it. Set the meter to its most sensitive resistance setting (X10,000 on a Simpson 260). Operate the control. The resistance should drop smoothly as you "turn down" the volume control--rotate it CCW. Due to the nature of this control, the drop will increase rapidly as you near the end of the control, but it should not jump or skip places, which would be caused by wear and fatigue. Check the very end of the control travel again with the less sensitive setting on your meter (X100 on the Simpson 260). The resistance should get quite low here. When set to the X1 setting, do not expect the resistance to go all the way down to 1 ohm. If it goes to 100 ohms or less, things are okay. If the resistance jumps around or cannot be brought down to a low level by rotating the shaft CCW, then the control is faulty. It must either be repaired or replaced. Since this control is not easy to find, I strongly recommend attempting to repair it, first. If you find that it needs repair, ask how. I can point out some methods of simple repair. If the control requires rebuilding, you will need to send it out for service. Other people on this site can point out several ideas and a few places for repairing the control.

Thomas

It appears to be the volume control, as you suggested.
It has been replaced in the past. I don't think it is worn out. It is smooth for resistance.
It is almost like the switch is mounted so that it turns off before the control is full down.
It ends up with over 6K ohms full ccw before off, and still 1K ohm when off.
(I should have caught the M for K, but it's been a long time.)

Dennis

:What "center tap" are you grounding? If this is the tap all by itself, then it will make little difference. The terminal right between the other two terminals should make a difference. Try grounding this. There are likely two reasons as to why your control is not working properly. One is that a connection to the low terminal is faulty either at the control or somewhere else. The low terminal is the one of the three that are close together that is to your left, with the three terminals facing down and the shaft facing you. This terminal is connected to ground or something else at a similar potential. I looked at several diagrams listed here. Yours is not listed (10-S-668). In the diagrams I saw, some had the low end of the volume control connected to the center tap of the power transformer high voltage supply, and some had it connected to a resistive network afterward. Simply follow the wire from this terminal within your radio and check all places that it is connected to.
:
:The other possible problem (probably more likely than the first problem) could be that the conrol is damaged itself. This could be caused by the resistive material being worn out at the low end of the control, which is very possible since this part of the control gets used the most (every time you turn off the receiver, and when you are listening to programs at anything other than a blaring level). It could also be caused by the control being cracked at this point or the terminal being loose on the control. To test for this, disconnect the low end terminal wire from this terminal. Connect your multi-meter with one wire to this terminal and one wire to the center terminal--the one right next to it. Set the meter to its most sensitive resistance setting (X10,000 on a Simpson 260). Operate the control. The resistance should drop smoothly as you "turn down" the volume control--rotate it CCW. Due to the nature of this control, the drop will increase rapidly as you near the end of the control, but it should not jump or skip places, which would be caused by wear and fatigue. Check the very end of the control travel again with the less sensitive setting on your meter (X100 on the Simpson 260). The resistance should get quite low here. When set to the X1 setting, do not expect the resistance to go all the way down to 1 ohm. If it goes to 100 ohms or less, things are okay. If the resistance jumps around or cannot be brought down to a low level by rotating the shaft CCW, then the control is faulty. It must either be repaired or replaced. Since this control is not easy to find, I strongly recommend attempting to repair it, first. If you find that it needs repair, ask how. I can point out some methods of simple repair. If the control requires rebuilding, you will need to send it out for service. Other people on this site can point out several ideas and a few places for repairing the control.
:
:Thomas

:What "center tap" are you grounding? If this is the tap all by itself, then it will make little difference. The terminal right between the other two terminals should make a difference. Try grounding this. There are likely two reasons as to why your control is not working properly. One is that a connection to the low terminal is faulty either at the control or somewhere else. The low terminal is the one of the three that are close together that is to your left, with the three terminals facing down and the shaft facing you. This terminal is connected to ground or something else at a similar potential. I looked at several diagrams listed here. Yours is not listed (10-S-668). In the diagrams I saw, some had the low end of the volume control connected to the center tap of the power transformer high voltage supply, and some had it connected to a resistive network afterward. Simply follow the wire from this terminal within your radio and check all places that it is connected to.
:
:The other possible problem (probably more likely than the first problem) could be that the conrol is damaged itself. This could be caused by the resistive material being worn out at the low end of the control, which is very possible since this part of the control gets used the most (every time you turn off the receiver, and when you are listening to programs at anything other than a blaring level). It could also be caused by the control being cracked at this point or the terminal being loose on the control. To test for this, disconnect the low end terminal wire from this terminal. Connect your multi-meter with one wire to this terminal and one wire to the center terminal--the one right next to it. Set the meter to its most sensitive resistance setting (X10,000 on a Simpson 260). Operate the control. The resistance should drop smoothly as you "turn down" the volume control--rotate it CCW. Due to the nature of this control, the drop will increase rapidly as you near the end of the control, but it should not jump or skip places, which would be caused by wear and fatigue. Check the very end of the control travel again with the less sensitive setting on your meter (X100 on the Simpson 260). The resistance should get quite low here. When set to the X1 setting, do not expect the resistance to go all the way down to 1 ohm. If it goes to 100 ohms or less, things are okay. If the resistance jumps around or cannot be brought down to a low level by rotating the shaft CCW, then the control is faulty. It must either be repaired or replaced. Since this control is not easy to find, I strongly recommend attempting to repair it, first. If you find that it needs repair, ask how. I can point out some methods of simple repair. If the control requires rebuilding, you will need to send it out for service. Other people on this site can point out several ideas and a few places for repairing the control.
:
:Thomas

OK. It is the Pot, and it is damaged at the low end.
I have it apart.
Is there a way to fix the damaged carbon?
Dennis

Open the potentiometer part of the control.

If the carbon is physically damaged--etched away severely or cracked, some in here suggest using a rear window defogger repair kit. I have never tried this, but I bet it'd work fine. If the control is just slightly worn with no severe wear, remove the C clip on the shaft and slide the shaft out of the control. Clean the carbon with a toothbrush and dish detergent. Dry well. Go to your automotive store and pick up some di-electric grease. Place a THIN film of this on the carbon surface and also on the center metal ring. Don't be messy. On the rotor bend the center wipers down slightly to increase tension (these contact the center metal ring on the carbon assembly). Bend the outer wipers down SLIGHTLY, but not severely, as this increases tension and wear on the carbon. Carefully bend them out radially as well--just slightly. Temporarily reassemble the carbon assembly with the shaft assembly. The outer wipers should contact a new surface on the carbon--the outer most wiper of the two should ride on the edge of the carbon surface. Disassemble the control again. Place some grease on the shaft and its bushing. Reassemble the shaft to the carbon disc and crimp on the C-clip with a pliers. Check operation with a multi-meter. With the switch facing you, operating lever at 6 o'clock, move the lever to the left. With the shaft of the potentiometer facing you and the terminals facing down, turn the control so that the outer wipers are at 12 o'clock. Straighten the tangs on the switch housing and place this over the control again. Bend down the tangs. Test operation with your meter and then test operation in the radio.

Thomas

I found a N.O.S. pot that was an almost perfect replacement. Only difference was an extra section, that I did't hook up.
Was a zenith part, but not the same number.
Even better: The replacement had the 2 taps. The pot in the radio had been replaced with a 1 tap replacement.
Sounds great now, and turns down normally.
Thanks,
Dennis

:Open the potentiometer part of the control.
:
:If the carbon is physically damaged--etched away severely or cracked, some in here suggest using a rear window defogger repair kit. I have never tried this, but I bet it'd work fine. If the control is just slightly worn with no severe wear, remove the C clip on the shaft and slide the shaft out of the control. Clean the carbon with a toothbrush and dish detergent. Dry well. Go to your automotive store and pick up some di-electric grease. Place a THIN film of this on the carbon surface and also on the center metal ring. Don't be messy. On the rotor bend the center wipers down slightly to increase tension (these contact the center metal ring on the carbon assembly). Bend the outer wipers down SLIGHTLY, but not severely, as this increases tension and wear on the carbon. Carefully bend them out radially as well--just slightly. Temporarily reassemble the carbon assembly with the shaft assembly. The outer wipers should contact a new surface on the carbon--the outer most wiper of the two should ride on the edge of the carbon surface. Disassemble the control again. Place some grease on the shaft and its bushing. Reassemble the shaft to the carbon disc and crimp on the C-clip with a pliers. Check operation with a multi-meter. With the switch facing you, operating lever at 6 o'clock, move the lever to the left. With the shaft of the potentiometer facing you and the terminals facing down, turn the control so that the outer wipers are at 12 o'clock. Straighten the tangs on the switch housing and place this over the control again. Bend down the tangs. Test operation with your meter and then test operation in the radio.
:
:Thomas

Superb! Keep the old control and try to repair it, though. They are rare. You may need it in the future, or you can use the original one in this radio again once you repair it (if you are able to), and then use this control in a different radio. If the carbon is really worn out, though, you will probably only have short term luck at best.

Thomas

:I found a N.O.S. pot that was an almost perfect replacement. Only difference was an extra section, that I did't hook up.
: Was a zenith part, but not the same number.
: Even better: The replacement had the 2 taps. The pot in the radio had been replaced with a 1 tap replacement.
:Sounds great now, and turns down normally.
:Thanks,
:Dennis
:
::Open the potentiometer part of the control.
::
::If the carbon is physically damaged--etched away severely or cracked, some in here suggest using a rear window defogger repair kit. I have never tried this, but I bet it'd work fine. If the control is just slightly worn with no severe wear, remove the C clip on the shaft and slide the shaft out of the control. Clean the carbon with a toothbrush and dish detergent. Dry well. Go to your automotive store and pick up some di-electric grease. Place a THIN film of this on the carbon surface and also on the center metal ring. Don't be messy. On the rotor bend the center wipers down slightly to increase tension (these contact the center metal ring on the carbon assembly). Bend the outer wipers down SLIGHTLY, but not severely, as this increases tension and wear on the carbon. Carefully bend them out radially as well--just slightly. Temporarily reassemble the carbon assembly with the shaft assembly. The outer wipers should contact a new surface on the carbon--the outer most wiper of the two should ride on the edge of the carbon surface. Disassemble the control again. Place some grease on the shaft and its bushing. Reassemble the shaft to the carbon disc and crimp on the C-clip with a pliers. Check operation with a multi-meter. With the switch facing you, operating lever at 6 o'clock, move the lever to the left. With the shaft of the potentiometer facing you and the terminals facing down, turn the control so that the outer wipers are at 12 o'clock. Straighten the tangs on the switch housing and place this over the control again. Bend down the tangs. Test operation with your meter and then test operation in the radio.
::
::Thomas