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.
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.
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.
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...
Had a similar issue on my 8S463, turns out it was the switch on the wavemagnet antenna that turns from local to distant.
"Not lighting up" - is the filament getting hot?
Thanks everyone! I’ll try these ideas tomorrow and let you know what happens.
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.
Did you check the 1meg resistor in the tuning eye cable?
I replaced that resistor in the socket earlier but I’ll check it to be sure it didn’t go bad.
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!