Red plating 6973....

[frankb]

I'm working on my Continental II  stereo amp this evening.  Restored it 30+ years ago and sounded great until recently.  I powered the amp up on my bench and noticed one of the 4 6973's has a glowing red plate.  I have -32V bias on it and 370V B+. It tests good on my Hickock 600 - (4000) with no shorts.  It continues to glow no matter which of the 4 sockets I put it in.  I'm getting down to my last few very precious spare 6973's.  I hate to toss it, is it really bad?  Anything else I should check?  The output transformers test good, no opens, no shorts.   I think the poor sound problem is from the fact that I never rebuilt preamp (control amplifier) years ago. 

-Frank B

[jukeboxmarty]

Since the amp uses more than one 6973, try swapping the tube into a different position. If it 'red plates' after it's moved, the tube is toast.

[frankb]

Darn, I was afraid of that.  Thanks for the reply.  The more I have to deal with these 6973's  the more I love 6L6's.

[jukeboxmarty]

Electro-Harmonix make a new "6973". Some people will debate whether or not these are true 6973's, but I've found them to be adequate in jukebox amps.