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Zenith 10-s-464 - Printable Version

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Zenith 10-s-464 - Tucker - 12-26-2018

I finished recapping this radio a few months ago and replaced the combination power/volume switch and the radio was playing good up to a few days ago. Now, after sitting unused for a few weeks it has hum that changes with the volume and the audio is distorted. I looked over the wavemagnet antenna and I don’t see any breaks in the wires. I also checked for continuity and all 5 connections on the plug make a connection inside the wavemagnet antenna. 
I’ve checked for B+ and it is present across both filter caps and I’ve retested all tubes and they’re good as well. I poked around with a plastic chop stick lokking for a loose connection or bad solder joint but found none. 
I’m thinking this is probably something simple that I’m overlooking but I’m not sure what to check next.

RE: Zenith 10-s-464 - morzh - 12-26-2018

Possibly a contact in a tube socket or a cold solder spot. Try to wiggle tubes, lightly tap them with a pensil, and then ith the chassis out and over, touch wires around with a plastic rod while playing the radio.

RE: Zenith 10-s-464 - Tucker - 12-26-2018

I tried wiggling the tubes and then tapping on them but nothing changed. I poked around underneath with a platic chop stick and everything seems fine. 
I forgot to mention that the tuning eye tube is no longer lighting up. 
I’m thinking I may have take the volages from the tubes to see if something stands out.

RE: Zenith 10-s-464 - sdradioman - 12-27-2018

Had a 12S370 that did the same thing... Needed the band switch cleaned again... Found that if I move the band switch through all the positions a couple times a week even if its not turned on, it doesnt have the issue anymore...

RE: Zenith 10-s-464 - NostalgiaRadioTime - 12-27-2018

Had a similar issue on my 8S463, turns out it was the switch on the wavemagnet antenna that turns from local to distant.

RE: Zenith 10-s-464 - Phlogiston - 12-27-2018

"Not lighting up" - is the filament getting hot?

RE: Zenith 10-s-464 - Tucker - 12-28-2018

Thanks everyone!  I’ll try these ideas tomorrow and let you know what happens.

RE: Zenith 10-s-464 - Tucker - 12-29-2018

I tried all the suggestions above and nothing changed.  But when I removed the tuning eye (6U5) tube and the radio plays good. I substituted another tube and it goes back to the same distortion. Removed the eye tube again and the radio is fine.  I poked around and wiggled each wire for the 6u5 socket under the chassis but couldn’t find anything.
Nothing is lighting up or getting warm on the eye tube.

RE: Zenith 10-s-464 - KCMike - 12-29-2018

Did you check the 1meg resistor in the tuning eye cable?

RE: Zenith 10-s-464 - Tucker - 12-29-2018

I replaced that resistor in the socket earlier but I’ll check it to be sure it didn’t go bad.

RE: Zenith 10-s-464 - Tucker - 12-30-2018

Problem solved, I had two of the wires mixed inside the tuning eye socket. When I pulled the tubes to test, the wires came out of the socket and got mixed when I stuffed them back in!