I have a Philco Transitone 51-532 on my bench. I've replaced all capacitors and several resistors. It is a run of the mill 5 tube set with an oddball mix of tube formats (LOCTALS, minis). The schematic is on Ryder's 21-46. When I bring it up, it plays nicely (clear signal and good volume) for about 30 seconds, then a quick *pop* followed by silence. What is my best practice for troubleshooting at this point? It sounds like a resistor, but which one and at which stage?
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I believe this set uses a 50L6 output tube. I would test the tube or try another tube. I recently did one of these sets and replaced the capacitors and resistors and rebuilt both IF transformers. Radio would play great for about 2 minutes and start to distort. I tested the 50L6 output tube and it tested good, but it the sound would distort after the tube warmed up. Replaced tube with a different one and radio plays great for hours. So I would try another tube and see if that helps.
+1
If that doesn't do it I'd have a look @ pin 3 of the 50L6 when it silent. Normally should see about 120vdc or so if it's way low check pin 4 if it's up @ 120vdc the output transformer is failing.