DRRI 6V6s red plating

[pchilson]

Not having a run of good luck this week...

What would cause the 6V6s in my DRRI to all of a sudden start to red plate?

It has been working great for months and yesterday while I was playing it it started to makes some staticy noises kinda like dirty tube sockets sound. It then started to hum loudly unchanged by the volume knob. I hit standby and let it cool a bit then turned it back off standby and it sounded fine again for a time. Pulled the covers off the back and plugged in my Bias-Rite and was getting extremely high reading that didn't make any sense. Bias readings that should be in the 18 to 27 ma range, I had it biased to 26ma at last I set it, the reading now were in the hundreds. I started to tap the tubes and thats when I saw the two 6V6s start glowing red then they would loose it again. Weird, I swapped the tubes around in the sockets and the readings then came back normal for a time, reset the bias to about 22ma and then the red plating started again. This seems to be an on again, off again occurance but short times between being right and being wrong.

Does this sound like bad tubes or something more circuit related?

The stock EH 6V6s I replaced with a couple old RCA 6V6s. I no longer have the stock tubes or any other 6V6s to swap in.

Whats the chances of this just being a bad tube?

[PremiumPlus]

Since both tubes are redplating, that is telling me that your bias supply is opening up somewhere, and not providing the negative voltage to the power tube grids to throttle them back. Look for a cold solder joint, bad (swollen) filter cap or maybe a bad bias pot. Anything that opens up in that negative power (bias) supply would do it. Should be easy to troubleshoot.

[52 Bill]

Since both tubes are redplating, that is telling me that your bias supply is opening up somewhere,...

A bad tube could cause the bias supply to be pulled down killing the bias to both tubes. I'd check the tubes first.

[pchilson]

Took the amp in to Glenn at Mars for warranty repair. They fixed it up right quick and sweet all on Fenders dime. Thanks Glenn. It sounds great.

[trem]

Took the amp in to Glenn at Mars for warranty repair. They fixed it up right quick and sweet all on Fenders dime. Thanks Glenn. It sounds great.

Sssoooooo, what was wrong with it?

[pchilson]

According to the repair ticket there was:
"repaired joint at C-36 capacitor"
"Rebias and tested"