[Gopher]

I noticed a significant channel imbalance last night and powered up and down my monoblock and preamps and plugged and unplugged the connections and eventually it sort of went away.

Today I fired up my rig and noticed the same obnoxious channel imbalance...  This time I broke out my multimeter and checked my biasing and noticed my left channel which had been biased to 88ma was at 93 while the right which was also left at 88 was at 38...

I've got my 845s cooling now and I'm gonna swap them each to the opposite mono and see what happens, but does this sound like bad tubes?  I sure hope not...  changing these 845Bs is a major PITA...

[Ericus Rex]

While your Treasures are en route you might think of taking this opportunity to have your amp checked out.  My only two power tube failures have been SPECTACULAR!  Nothing like what you're describing (though not 845's).  What you're describing could be a tube failing I s'pose, but it could also be a problem with the bias network of your amp.  While this situation currently sucks, what would suck even more would be to put your new Uber-expensive Treasures in and the amp kills them in two weeks.  Better safe than sorry...and poor.

[Steve]

I noticed a significant channel imbalance last night and powered up and down my monoblock and preamps and plugged and unplugged the connections and eventually it sort of went away.

Today I fired up my rig and noticed the same obnoxious channel imbalance...  This time I broke out my multimeter and checked my biasing and noticed my left channel which had been biased to 88ma was at 93 while the right which was also left at 88 was at 38...

I've got my 845s cooling now and I'm gonna swap them each to the opposite mono and see what happens, but does this sound like bad tubes?  I sure hope not...  changing these 845Bs is a major PITA...

You might check out other parts, but the measurements sound like one tube is failing; the 88 ma to 38 ma tube. The reason the other tube's idle current rose from 88 ma to 93 ma is because the plate voltage rose due to less overall plate current. But it never hurts to check out the rest of the circuitry just in case another part is failing.

Hope this helps.

[Gopher]

Hmm...  I've read of the same thing happening with failing 845s before, but it was from the first couple usages rather than happening after months of perfect operation... I'd HATE to kill a Pavane....

My only issue is my amps are big and heavy (like 60 pounds each) and their boxes BARELY fit in my sedan...  Shipping them out for a checkup would not be cheap or convenient.  If it had to be, fine--they're warrantied and would go back to Pacific Valve, but I don't know what I'd do otherwise to check them out...

[Berto]

Fred , I would also worry bout cooking a expensive tube as well, esp when you're not sure about the root of the problem

Not sure if its even a good option for you but I know a very inexpensive and insanely knowledgable amp tech (hard to believe I know) that lives in queens and fixed my Audio Aero amp. Something was cooked inside. Helps also if can get the schematics for the amp and he can pinpoint quickly.

[rpf]

Fred , I would also worry bout cooking a expensive tube as well, esp when you're not sure about the root of the problem

Not sure if its even a good option for you but I know a very inexpensive and insanely knowledgable amp tech (hard to believe I know) that lives in queens and fixed my Audio Aero amp. Something was cooked inside. Helps also if can get the schematics for the amp and he can pinpoint quickly.

Fred,

I second this advice. It could be a lot cheaper than shipping a heavy amp(s) back and forth. I don't know if Berto is thinking of the same tech I am but I'll post my rec. SG Custom Sound (Scott Gramlich), in Douglaston, Queens, very close to the Cross Island Pkwy. 718 224-5083

Rob