2. amps-preamps
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How to track down bad tube and what can it mean?

I recently changed the tubes in my preamp and all but the driver tubes on my amp, but these tubes didn't work out. I replaced these with the stock tubes which had been good before. Now I get distortion from the left channel which sounds like a buzzing that comes and goes with the music. It increases with the volume. I've checked all the tubes and they are placed OK. At one point with the volume loud but not too loud the system turned itself off which had never happened before. My speakers are efficient and it was not putting out more than 10 wats max when this happend.

So how can I track down a bad tube if I have one? I suppose I could replace the tubes one by one with the new ones I tried, but this is extremely tedious and makes me dream of SS. Any idea what this problem, this sound indicates?

Any help is appreciated. My sick system depresses me. Thanks.
budrew
budrew OP
467 posts
 
I put the stock tubes back in both components and that's when the problem started. The new tubes I tried then removed were Electro-Harmonix purchased from Tubeworld. The amp is the Mcintosh MC2102 and preamp is C2200.
listener57
730 posts
 
At Radio Shack, there are non-shedding replacements for Q-tips so no particles accidentally transfer from tube pins into tube sockets. Another way to go is to use tiny, pointed, non-shedding eye cosmetic applicators from the cosmetic section at any pharmacy. These are what seem to be included with the wonderful Walker Audio SST contact enhancer, for use on tube pins, only after your mystery problem has first been definitely solved. Caig makes contact cleaner-enhancer suitable for tube pins, but other Audiogon members can comment whether there is any type, and concentration, of ordinary alcohol also acceptable for preliminary cleaning of tube pins.
Owning tube equipment is more fussy than transistor equipment, and I have been saved more than once from the sound of silence, by having at least one backup tube of each type used in my components. This is one of the prices paid to stay on the side of the angels.
budrew OP
467 posts
 
I'm frustrated because I'm stuck here at work in meetings and all I want to do is trouble shot my tube problem : ( But I suppose we have to earn the money to pay for this hobby, eh.

It occurred to me I can try switching the channels for the speaker connections. This may not help with much but at least it will clarify if in fact it is a speaker problem. I have no reason to believe there could be a problem with the speaker, but it's one more thing I'd like to rule out for sure.
unclejeff
1,313 posts
 
McIntosh 2102? I have that amp. The stock tubes used to be Svetlana KT 88 and a bunch of Chinese-made smaller tubes. I understand that the newest 2102 amp has Electro Harmonix Kt 88s, but I don't know what the rest are.

My 2102 sounds great with the Svetlana tubes and I traded out the 12AT7 tubes for some 1960-era Sylvania and the 12AX7A to Electro harmonix. This made a terrific differance as the stock tubes never reached my espectations.

I am told that the Electro Harmonix KT 88s are fine, but if McIntosh is still using those Chinese other tubes, junk them.
budrew OP
467 posts
 
I don't know if I should feel stupid or relieved. I switched speaker cable channels and the problem still occurred in the left channel. I was sure it was not a speaker problem but I checked it out to see what was what. It turns out there is a ficus tree next to the left speaker that had grown a limb between the speaker grill and the bass driver and when the bass driver started thumping some of the leaves were vibrating off of it. Doh!!!

I'll check into the EH KT-88s. My amp is from late last year. I still have the EH tubes and may try them again someday.

Anyway, thanks to you all!
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