How to track down bad tube and what can it mean?

Thanks folks. I'll have to spend some time this weekend on this detective effort. The sound, a buzz that reminds me of a blown speaker though I did nothing to effect the speakers this way, appears with whatever source I have selected. This morning I switched interconnects between preamp and amp and the sound was still coming from the left channel. I'll try switching the left and right tubes in the amp and see where that goes.

Do you use a Q-tip to clean the tube pins?

If necessary I'll take the amp in for service, but it weighs 100 lbs so it's a freakin pain in the arse.

What did you buy for new tubes, and from whom? Are you still using the new tubes in your preamp, amp, or both? What make is your preamp and amp (monoblocks?)

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.

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.

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.