The 1960's GE Musaphonic
 

I got this very nice sounding tube radio at The World's Longest Yardsale the summer before 7th grade (Years ago...) for only $1. It works good, but is tempermental. Sometimes, if it is on longer than 15-25 minutes, it will start popping, cutting out, and will ultimately go silent. I was listening to it tonight on AM, and the song "Cats in a Cradle" came on, and it made it through the song, then started cutting out. The model No. is unknown, as the sticker was replaced by a hand drawn schematic for the tubes.

Ge made their own IF transformers, at the time. They were a bit more susceptible to silver mica disease, which is a term for breakdown of the mica capacitors, in the base of the IF transformers. :thumbsdn:

Is the radio tube or solid state? If solid state, it is likely the audio output transistor.

It's a tube job!
Don't know if it's a six tube, with a tuned RF stage. Good sounding and a great DXing machine. :thmbsp:

Before I condemned the IF transformers (which, could very well be the trouble), I'd clean the tube sockets and controls with contact cleaner. Then, I'd check the solder connections on all tube sockets and surrounding areas. Tubes and PC boards really don't need to mix; but, companies thought differently and the result often ends up being damaged tube sockets, damaged PC board traces, or cracked solder connections. If the problem is still there, try tapping each tube with a pencil or similar object. If tapping a particular tubes causes the problem, you likely have an intermittent tube that will have to be replaced. The symptoms of bad IF transformers are static burst in the audio that sounds like a thunderstorm. When the IF transformer is bad in this way, you can usually check the grid voltage of the tube that's being fed by the suspected IF transformer and if the transformer is bad, you'll see a varying positive voltage on the grid.

Unfortunately, it's getting hard to find good IF transformers and even NOS ones can shortly develop the same problem. The only permanent fix is to take the IF transformer apart, determine what value capacitors are used, disable the internal capacitors, reinstall the IF transformer, and mount outboard capacitors to the underside of the PC board.

Also, when left on for a long time, it will start going loud, then quiet, then loud, then quiet, etc. If I put my right hand (not left) the audio suddenly improves, then degrades dramatically when I take it away.

Does the level of this popping noise vary with the volume control setting? If so, the source of it would be 'upstream' of the volume control, i.e., in the IF strip or earlier.