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Original Message

RE: Tube dampers etc.

Posted by Lew on April 10, 2016 at 10:04:40:
Mr. Derrick, This may be in agreement with what you are saying, but if you have a way to measure "noise" of a tube, other than simply to insert it in the circuit and listen to music (which is not a bad way to do it), it's probably best to use the quietest tubes in the gain stages. The driver stage, and the circlotron output stage of the preamplifiers, does not add any gain, so in fact you can better get away with using noisier tubes in the driver stage. Same goes for the CCS, although I say that with less certainty; the CCS constitutes a very high impedance circuit, so it would block noice from the distal side, at least.

Apropos the talk about microphonics, I am facing the fact that I should get rid of my beloved KenRads from the linestage gain section of my MP1; they have become hopelessly microphonic, where once they were tolerably microphonic. They've gotten much worse lately. O-ring tube dampers are not helping at all. ("Microphonic" is not quite synonymous with "noisy", but it's one way in which tubes can add noise.) KenRads have all had this problem to one degree or another, but I am addicted to their sonics; I just try to pick the quietest ones from my diminishing stash. I am going to try Brimars next, which I know are NOT microphonic but are not quite as magical as KenRads.