Zenith 10S690 Volume Control Issues

[old_coot88]

Do you get any noise when turning the bandswitch, or is it silent?

[vortalexfan]

Originally Posted by old_coot88

Do you get any noise when turning the bandswitch, or is it silent?

All I get is the electrical sound of the band switch making contact at each position and when I tune through the tuning dial all I get is a hissing noise across the dial.

I disconnected the B- Wire Lead from the volume control like you told me to when I was testing the continuity of the volume control and I also disconnected a capacitor that went to that terminal as well, but I reconnected them just like they were originally and I wouldn't think that disturbing the B- connection to the volume control pot would mess with the radio's reception capabilities.

The aforementioned disconnecting of the wires from the negative terminal of the volume control pot was the only thing I disturbed in the radio this time around, so I'm kind of confused as to what could of happened to make the radio lose reception.

[old_coot88]

Check that there is plate voltage on the 6A8 and 6K7 (pin 3 of both tubes).

Also check screen grid voltage on both tubes (pin 4 of both).

[vortalexfan]

Originally Posted by old_coot88

Check that there is plate voltage on the 6A8 and 6K7 (pin 3 of both tubes).

Also check screen grid voltage on both tubes (pin 4 of both).

Geez this radio is turning out to be a pain in the butt, because I have to put the radio in the cabinet to test it (the antenna is in the cabinet and the radio won't work without that antenna attached to it) and the speaker is too big for me to take out of the cabinet and plop it on my bench next to the radio, so I have to keep removing and installing the radio from the cabinet to do all of these tests.

So what are you thinking may have happened if you don't mind me asking?

Also I rechecked the radio and it is indeed dead silent except for the popping noise it makes when changing the band switch, there is absolutely nothing on the radio reception wise when tuning through the dial not even a little bit of static or hiss.

I also checked all of the tubes and they all tested fine (they are all the original Zenith branded Tubes to this radio except for the 6A8 tube and the 5Y4 Rectifier tube which are RCA and GE Branded tubes respectively.)

[old_coot88]

Do you have a spare 6A8 to try for a sub? If not, try wiggling the 7G7, 6A8 and 6K7 in their sockets (with power on, volume high). Also try tapping them to check for intermittents.

This is a dumb question, but is there any chance the 6A8 and 6K7 coulda got interchanged?

[Electronic M]

Some 40s Zeniths would go stone deaf if the wave magnet wasn't connected. Don't forget to connect it for your tests.

[init4fun]

What tube is the parallel caps shown in this picture connected to ? If it's anything "front end" related (RF amp /osc / or mixer) and it's in a grid circuit , the parallel caps may have thrown the circuit out of alignment ?

[vortalexfan]

Originally Posted by init4fun

What tube is the parallel caps shown in this picture connected to ? If it's anything "front end" related (RF amp /osc / or mixer) and it's in a grid circuit , the parallel caps may have thrown the circuit out of alignment ?

those are the coupling cap for the 6V6s (the original was a .05 MFD but the closest I had at the time that I replaced that was 2 .033 MFD caps which I paralleled to make a .06 MFD cap.

So nothing to do with the front end.

[vortalexfan]

Originally Posted by old_coot88

Do you have a spare 6A8 to try for a sub? If not, try wiggling the 7G7, 6A8 and 6K7 in their sockets (with power on, volume high). Also try tapping them to check for intermittents.

This is a dumb question, but is there any chance the 6A8 and 6K7 coulda got interchanged?

I never touched any of the tubes when I was recapping this radio or when I undid the B- wiring from the negative leg of the volume control.

The only time I touched the tubes was to test them in my tube tester to make sure there weren't any dead ones, but I disconnected them one at a time so that there wasn't a chance for them to be put into the wrong socket.

I don't have any spare 6A8 tubes unfortunatly, and the weird thing is that the original owner of this radio replaced the original 6A8G tube with a metal 6A8 tube so because of that they ended up throwing out the original tube shield that went in that spot and unfortunately the metal 6A8 tube doesn't fit into the tube socket very tightly like the original 6A8G did so I have a feeling that the replacement 6A8 tube may not be making very good contact with the tube socket because the tube pins don't seat all the way into the tube socket.

I also checked the 7G7 tube and the pins looked kind of crusty looking but I wasn't sure if that would of caused the issue I was having or not (I know Loctal tubes are notorius for making bad contact between the tube pins and the socket).

[vortalexfan]

Originally Posted by Electronic M

Some 40s Zeniths would go stone deaf if the wave magnet wasn't connected. Don't forget to connect it for your tests.

I know, I double checked to make sure the connection was good between the wavemagnet and the radio chassis and it still seems unresponive.

[vortalexfan]

OK so now I'm getting some static sounds out of the tuner at the spots where the stations would be coming in at but still no audio or reception.

I tried wiggling the tubes you suggested I wiggle (the 6A7 and the 7G7 tube) and it didn't make much difference.

So another question, can having the chassis not being completely tightened down to the cabinet cause reception issues?

[old_coot88]

Originally Posted by vortalexfan

... can having the chassis not being completely tightened down to the cabinet cause reception issues?

Can't think of any reason how/why it should. Question- is there any way the cabinet can be laid on its side, and the chassis slid back far enough to take voltage readings in the RF and IF areas? Or is this a large floor-standing console?

(Back in the day, this was a common accessability practice in TV service, even with console sets. It was usually done with the heavy end of the chassis down.)

[vortalexfan]

Originally Posted by old_coot88

Can't think of any reason how/why it should. Question- is there any way the cabinet can be laid on its side, and the chassis slid back far enough to take voltage readings in the RF and IF areas? Or is this a large floor-standing console?

(Back in the day, this was a common accessability practice in TV service, even with console sets. It was usually done with the heavy end of the chassis down.)

This is a large Phono/Radio Console it's kind of hard to tip it on its side.

[old_coot88]

This is a long shot, but.... in post# 10, fourth photo, near the center of the shot, there is a 330K (orange-orange-yellow) resistor. To its left is a yellow capacitor labeled 333K 630V. A bare lead from the resistor looks to be lying directly across a bare lead from the capacitor when you blow up the image 300%. It may just be the camera angle, but would be worth checking.

[vortalexfan]

Originally Posted by old_coot88

This is a long shot, but.... in post# 10, fourth photo, near the center of the shot, there is a 330K (orange-orange-yellow) resistor. To its left is a yellow capacitor labeled 333K 630V. A bare lead from the resistor looks to be lying directly across a bare lead from the capacitor when you blow up the image 300%. It may just be the camera angle, but would be worth checking.

I think that's an illusion, because the resistor you're referring to isn't actually touching that capacitor because it's about a 1/4" higher than the capacitor.

Well. I'll try and take the chassis out of the cabinet again and attempt to get the speaker out of the cabinet to put it on my bench and see if I can get some voltage measurements, the only reason why I didn't want to monkey around with taking it out of the cabinet is because with my cut on my knuckle it's hard to unscrew the screws without hitting my knuckle against the cabinet.