microphonic preamp

[Andy Le Blanc]

ampdoc1, what do you mean by "usually install grommets on the tube bases"?
Now I tend to like a lower gain, simpler amp and don't run into issues
generally associated with high gain. Is it a simple gasket where the socket
is mounted? An isolation mount?

[Structo]

Something that was mentioned in this forum before and sorry I don't remember who said it, was to use large heat shrink tubing to dampen the tubes.

Cut some that will cover the top half of the tube then heat it to shrink.

I have used the silicone O rings in the past that helped a little.

But the shrink tubing would still allow the use of tube shields or wire retainers.

[ampdoc1]

Andy,

I just use small rubber grommets in the preamp socket chassis holes, then don't turn down the screws too tight. Seems to work well,...at least I hadn't run into the tube feedback/noise problem in any of the other amps I've constructed this way.

Mesa used to heat shrink some of their 12AX7s, and I've see o-rings, rubber bands, and just about anything that is absorptive used to dampen the preamp tubes.

Obviously this is an issue that is typically more prevalent with combo amps, since there is nothing to cushion the tubes from vibration.

a'doc

[fishy]

My first tw build was a liverpool and it suffered from V1 being extremely microphonic.
Chopsticking highlighted my plate leads to be an issue. Just touching them sent the tube off.
I rewired the socket and paid more attention to the wiring dress. This cleared most of the issues up. A better tube in V1 improved the situation further. It still is a little microphonic but vastly improved. Keeping the head off the speaker cabinet prevents it from happening at all.

[Andy Le Blanc]

I've played with mounting the sockets directly to the component board. Its
not too hard to do with a hand build, maybe that and mounting the board with
isolation mounts. The O-ring under the tube socket seems so much more elegant.
Heat shink seems also to be very easy, at least for new tubes, I wouldn't do that to my telefunkens.

[lumox0013]

thanxxx to all who chimed in I reduced the problem but couldnt eliminate it so I decided to start over better luck next time? I hope. but I wanted to thank ya'll for all the help.