Power tube socket arc diagnosis

[ampgeek]

I have a friends dead Silverface Vibro Champ (AA764) opened up and see a vaporized path between the plate and filament pins on the back-side of the power tube socket.

I replaced the socket with a new ceramic unit (as well as the rectifier base as its sockets were loose and wonky) and have wired it all back up.

Passed the bulb limiter test with no tubes and with just the rectifier and pre-amp tubes. All voltages around the recto and small bottles look reasonable considering no output tube is installed (e.g. plates and cathodes a tad higher than published values).

I stopped just short of plugging in a new JJ 6V6S to ponder what might have caused the arc-out in the first place.

The zapped tube base looks to be original issue (micalex?) and appeared fine to the eye otherwise.

Any thoughts on additional diagnosis before throwing in the JJ 6V6S and giving it a go?

TIA,
Dave O.

[martin manning]

The filament circuit was the path to ground, but it's ok, I guess, since you have it powered up and working. The most likely cause is running without a load, so I'd check the speaker connections carefully.

[ampgeek]

Right on Martin!

I hadn't yet powered it up with an output tube installed so I wouldn't have given it the path to ground with the new socket installed.

Sure'nuff.....I am not measuring any continuity across the speaker terminals. Nor the wires that run off into the bowels of the speaker.

Many thanks!!

Dave O.