Tube issues, 12at7 affect KT88?

Well whatever the problem with that tube is it's causing that KT-88 to run away. Usually, if the DC voltage operating points are upset, that will upset the balance of the amp and over drive the output. Or for some reason the bias on that KT-88 is being affected and your loosing negative bias voltage on that tube. I believe in the vintage 275 the 12BH7's are the driver tubes. Is this a new 275 or a vintage 275?

Version V, newest version.

Heyraz, you are absolutly right. I am considering purchasing a tube tester.

HiFigeek, the weird thing is, only one tube runs away. I don't have the wiring schematic, but I'm guessing the first 2 AT's run the first 2 KT's, and the next 2 AT's run the next 2 KT's, with the 12AX's leading? That is what makes me think I have it narrowed down to 2 of the 4 AT's.

Tony

Tony what's the last tube in the chain before the KT-88s?

If you have a DMM, you might find a short or open on your suspect tube by comparing it to a known good tube. Look through the tube, see where the wires are going and check those pins for opens or shorts. I learned that trick from a friend last year. It won't tell you the tube's quality, but it will identify an open or short. You can use this method while you're looking for a tube tester.

Hifigeek, looking at it from the side, back row is 4 KT88's.

Front row is 2 12AX, 2 12AT, 1 12AX, 2 12AT. I remember reading the first 12AX is only needed when run in stereo and not mono blocked. So I am assuming 2nd 12AX and 2 12 AT for first 2 KT's, 3rd 12AX and 3rd and 4th 12AT for last 2 KT's. But that's just a guess. It is the 2nd KT that gets hotter, which makes me think it's one of the first 2 12AT, probably the 2nd if my guess is correct.

Heyrazz, what is a DMM? Eyeballing the tubes, it appears everything looks connected.

Continued thanks,

Tony