Problems with the tuning of my Zenith C835 radio.

pete1729

Super Member
I thoroughly recapped this unit ten years ago with modern electrolytics and it has been pretty much a daily driver since then. It was playing nicely up until yesterday. I moved it from one spot in the kitchen to another and it developed a problem tuning in FM. I did not handle it roughly in any way. At first it would only tune in stations around the middle of the dial, but this morning it doesn't want to tune in any station. I get some sound but it sounds like two or three stations and some static that changes a little as I turn the dial. Sadly I do not have a schematic nor can I find one on line. Any ideas?
 
Generally. Check voltages at various points, check for out of spec caps/resistors. I have a pretty decent meter. I guess I'm looking for advice along the lines of 'It sounds like a tube in the RF section' or 'It sounds like a bad component'. The former means just pulling off the back, about 20 minutes. The latter means pulling out the chassis which will take me an evening.
 
My daily driver started doing something like this and what brought it back for me was cleaning the dial string (alcohol), a drop of oil on the tuning shaft bearing, and deoxit/reseat the tube pins.

I like doing the "no parts" things first in case they do solve the issue. And when they do, I dance a little jig.

Btw, that's one cool looking radio.
 
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Troubleshoot it. You do know how don't you?

Actually I think I see your larger point. Even if its just a tube it just makes better sense to fully diagnose the problem. I'm going to order up a copy of the RF tube, it's a 6BJ6, but I'm going to pull the chassis and check it all the way out before I possibly sacrifice a replacement tube.
 
My daily driver started doing something like this and what brought it back for me was cleaning the dial string (alcohol), a drop of oil on the tuning shaft bearing, and deoxit/reseat the tube pins.

I like doing the "no parts" things first in case they do solve the issue. And when they do, I dance a little jig.

Btw, that's one cool looking radio.

IMAG0193_1.jpg
 
AM is out too.

If you have audio, and it varies with the volume control, that narrows it to something common to FM and AM, which means the IF tubes and the AM/FM selector switch. I would try to work the switch back and forth and see if that works. If not, try to substitute known good tubes for the IF tubes, and see if that wakes it up. If not, then it's time to take it to the bench. Be aware that if it has the small IF cans, silver mica migration is an issue inside IF cans of this era, so if you also head some static and crashing type sounds before it failed, you may be in for rebuilding the IF cans.
 
I forgot I had a parts unit in my basement. I pulled the 6BJ6 from that unit and a couple other tubes from next to the tuning gang and swapped them in. Problem solved. In the long run I plan to go through the radio thoroughly, checking all the components and voltages, then retube it. It's really a fine radio.

Thanks everybody.
 
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