[spfradios2]

Actually, it was not charred. I took it apart just in case the break was observable. Not sure about corrosion. I've seen it before, but this transformer looked clean... no copper sulfate stains, etc.

Continuing on with the issue... I attended the MARC Extravaganza, Lansing, MI, yesterday. I met a very interesting man from Melvindale, MI who is 92. He said he was a radio repair man before the radio I'm restoring even hit the market. (By-the-by, his chemistry teacher in high school was Charles Lindbergh's mother.) He said my theory is not exactly what really cooked things. First of all, there is no current to speak of in the grid circuit, so it's not like a grid resistor will burn out. He said if it was a high current issue, the root cause was the coupling capacitor connected to the 6F6 grid. It was probably leaking severely, thus wiping out the grid bias and the tube went to saturation. He said that if you really want to protect the primary of the audio interstage tranformer, just make sure the upwind coupling capacitor is very healthy. He suggested a 1000 volt to make it last beyond my life.

When I got home, sure enough, that capacitor was nearly fully shorted out, probably delivering a lot of B+ to the grid.

Whether it was corrosion or high current, at least I learned something from a really neat guy with a wealth of knowledge.

Thanks all,
John