microphonic EH KT90's

[Tage]

I am using some KT90 tubes o n a home build bass amp and I've noticed that they pick up a lot of the cabinet vibrations and rattle really bad especialy when i play on the E string of my bass. I was just wondering if anyone else has encoutered this issue with these tubes.

[Enzo]

Put it the other way. Has anyone seen a type of tube that has never been microphonic?


ANY tube can be microphonic.

[Tage]

ok fair enough, i think it is mostly due to the fact that my chassis is thin steel and it vibrates too easily. i'm gonna brace it and see if that helps. I was just curious if anyone else found these power tubes especially microphonic.

[soundguruman]

Sometimes, if the layout of the amp causes some preamped signal to loop back into the input,
It can "seem" as if the output tubes are microphonic.

But changing the layout or installing shielding can stop it.

Also, reverse drive or reverse output transformer phase can cause what seems to be microphonic output tubes...

But it's true, all tubes under certain circumstances or in certain circuit will exhibit microphonic tendencies.
There is no tube which is non-microphonic.

Although Aspen Pittman will tell you his Groove Tubes are not microphonic...it's just a fantasy.
(remember me Aspen? "there is no such thing as a non-microphonic tube?" That's me again! hope you are well, happy hollidaze!)

I was working with a JCM 4100U, that seemed as if the power tubes were microphonic.
But it turned out that the reverb tank wires were too close to the input jack.
By shielding the input jack from the reverb wires, the problem was gone.
And so, it was the layout that was causing it to LOOP and whistle, like a microphone.
Layout is pretty important and makes all the difference, as we have said many times before.

[Tage]

yeah my problem is mostly a mechanical rattle now, not so much a microphonic issue. i think i have it beat. i think these big envelopes on the power tubes just done like my vibrating chassis too much.