I am restoring a Gambles-Skogmo radio, model 43-7604, and have it receiving and playing once again (recapped, couple of resistors replaced, tubes say OK on tester), but there is one issue that I don't know what to do about.

When I turn it on from a COLD start, there is only silence, even after it has had plenty of warm up time (minutes). It's not completely silent. Listening to the speaker you can tell the radio is turned on but there isn't a disctint sound coming out. No hum or buzz or whine. You just know that the device is on. And tuning up and down the dial doesn't change anything.

But after warm up, if I turn the radio OFF then ON again one time, everything is fine and the signal is loud and clear.

I'm not sure what this indicates but I have to believe that cycling the power like this can't be too healthy in the long run.

Any ideas? Time for some Cold Shot?

Randy

You can isolate it by gently rocking each tube when the set is on, as the set will come on when the problem tube is encountered. If it does come on there are two possibilities right in that area.

You might have an issue with a "cold solder joint", where the wiring or component leads are not fully flowed with solder.

It could also be a corroded pin or dirty where a pin has intermittent contact because of corrosion or dirt. If you have a real hobby shop near you, get some "Rail Zip", and put enough onto each pin to make it slightly wet, and plug into the socket and work it around gently.

One other possibility if you used NOS parts, a paper cap may have been coming apart internally. A shot of cold shot might reveal it, but gently pushing against the body with an insualted screwdriver is good enough to reveal it too.

:I am restoring a Gambles-Skogmo radio, model 43-7604, and have it receiving and playing once again (recapped, couple of resistors replaced, tubes say OK on tester), but there is one issue that I don't know what to do about.
:
:When I turn it on from a COLD start, there is only silence, even after it has had plenty of warm up time (minutes). It's not completely silent. Listening to the speaker you can tell the radio is turned on but there isn't a disctint sound coming out. No hum or buzz or whine. You just know that the device is on. And tuning up and down the dial doesn't change anything.
:
:But after warm up, if I turn the radio OFF then ON again one time, everything is fine and the signal is loud and clear.
:
:I'm not sure what this indicates but I have to believe that cycling the power like this can't be too healthy in the long run.
:
:Any ideas? Time for some Cold Shot?
:
:Randy
:

Of course this has something to do with a bad component, but what could also be happening is one of the circuits could be breaking into oscillation when the radio is slowly warmed up, but is jarred out of oscillation when the set is turned off and back on quickly. I have had several radios do this for various reasons--faulty AVC components, other various condensers. My RCA 55X still does it, and I haven't fixed it yet. My Zenith 5-G-500 used to do it because of a weak 1LA6 tube. It was weird in that the radio would work when it first came on, but everything slowly got hollow and ventrilloquistic with a sort of a shreak, and then "pop," everything went dead. Turning the set off and then back on brought things back to life. Surging the tube on my tube tester using the highest current setting (#4 on an Eico 625) would rejuvenate it for a couple of weeks. Replacing the tube solved the problem. This radio also had almost the same problem at another point in time when the filament ballast resistor started leaking into the condenser isolated chassis. This would charge up the chassis with DC. The set would go into a hollow shreak really quickly, and then "pop," everything went dead. In this case I had to discharge the condenser.

In your case, if this is happening and there is any shreak or anything of that sort, it must be happening before the audio stages warm up, as you say you don't hear anything. Sometimes, too, when a circuit breaks into oscillation, it'll simply "pop," and all will go quiet. You may hear a rushing sound of sorts. The pop may happen before your set warms up, which would be why you wouldn't hear it. The RF section is usually where things like this happen, and RF tubes usually warm up before AF output tubes.

Anyway, if your set doesn't simply have a faulty component or connection, it may be breaking into oscillation.

Thomas