the OD3 does matter!?

[rogerfederer]

i've been on a campaign to solve the microphonics problem.  tried new tubes, better isolation, weight on the top plate.  even with my 3 lb scuba weight on the top of the trafo i was still getting noise.

i had picked up 2 vintage OD3s locally (sylvania and westinghouse).  when i rolled them in earlier i hadn't noticed a difference.  for whatever reason i put back in the OD3 that came with the kit and the noise is now gone.  listened a whole day and no microphonics at all.  (on a similar note, i'm back to the 4P1Ls that came with the kit as well.)

i assume this is all cumulative.  the weight on the top plate probably has been the biggest step forward.  voltage regulator?  darned if i know what that tube is doing but it can influence the microphonics. 

[rogerfederer]

OK, getting a little noise here and there, but much reduced.  probably related to someone walking around on the floor above. 

i'm now thinking the 4P1Ls i'm using are a set i bought on the auction site, but i'm not positive.  did the tubes with the kit have little yellow stickers on the base?

[Paul Joppa]

Watch the inside of the 0D3. Glow tubes often have a particular current at which the glow is only marginally stable - a patch will move from one place to another seemingly at random. This causes a kind of noise.

Fortunately, the critical current moves around as the tube ages, so if you have it it will go away after a while. Of course, if you don't have it, it will probably appear at some point....