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In Reply to: 6v6 triode connected as voltage amp posted by mikeyb on March 1, 2007 at 17:37:53:
but thought to be microphonic in some circuits.
So much for my memory. You are correct, the 27 is a IDHT and I have not tried one. I have tried the 26, and it's microphonic (at least the one that I have).
I am playing now with 26. Filament power does require extra work. Most folks perform this work in the form of DC arrangements, batttery or CLCLCLC filtering. I am using AC, but need separate supplies for each tube and have 2 tubes in each channel, so for stereo need four 1.5v at 1.05A supplies. I also need a hum pot on each tube. AC is a great way to go, but it is not as easy as AC on an IDHT.
I have found microphonics of the 26 damped in a stacked Aikido-style arrangement. In other circuits I tried the same tubes were much more microphonic. In fairness, I am getting a gain of one-half mu, call it a net of 4, so that may explain where the microphony went.
Thanks for the informative reply! So can you achieve acceptable hum levels with AC on the filaments? If so, I would prefer to go with AC.
I can achieve a respectable level of hum -- all but inaudible in my headphone amp. When I had only one channel built, it was inaudible, but with two channels there is a teeny bit, which I think may be induced somewhere in my spaghetti mess of wires.
I wrote up my work on this a while back. A schematic appears here, thanks to helpful inmate Jose K:
click the connecting posts to that one and find more of my effusions on the topic.
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