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I think I got to the bottom of this mystery. Tightening up the socket jacks helped. Using thicker gauge wire on the filaments helped.

There remains a slightly diminished output in the right channel. I suspect a cold solder joint - somewhere.

Since I had not removed the power tubes for 2 years, I do not know how the sockets jacks lost tension (or contact). Heat? Vibration? The sockets jacks and the pins of the tubes are not at all corroded.

The pins on some of the newer tubes, and probably the JJ's
are too thin, and the sockets don't grip them very well to
begin with. A set of new sockets would be a worthwhile
fix, or just get in there with a tiny jewelers screwdriver and
tighten them all up.

This amp is truely possessed.

The right hand filaments have a 3.07V per side reading.

The left hand have a 3.30V reading per side.

Cold solder joint? Right hand filament supply crapping out?

kheper wrote:This amp is truely possessed.

The right hand filaments have a 3.07V per side reading.

The left hand have a 3.30V reading per side.

Cold solder joint? Right hand filament supply crapping out?

The left side filaments have 6.6V end-to-end.
The output power is probably at 66W.

Call it "ST-66".

This may be a good time to replace the power tubes/sockets (re-pent-ode), move away from those evil radio broadcast transmitters and Three Mile Island, and make offerings to Saint Jude.

Matt

Probably have to perform a few animal sacrifices, too...

TMI and UFO's can cause some really nasty troubleshooting issues


/ed B

I rebuilt the bias supply with 2 6.6k resistors and 2 Nichicon caps.

I put a quad of new-production Tung-sol KT66s into the amp.

The KT66s have a nice bottom end, but they seem to lack "something".