Expanding questions about tubes in a preamp

Describe in detail what extraneous noise you are experiencing.

If it's "hiss" from the tweeters, then dampers are not the solution (cabling type and placement of the cables/gear would be as well as shielding unused inputs with shorted plugs).

I posted to your prior query and will add that your unusual preamplifier (which may be modified - due to it using a 12ax7 in place of a 12au7, which was standard in the original design) now uses two extremely high gain tubes (12ax7/EF86).

The original 12au7/EF86 design makes more sense (on paper anyway;-).

As far as micro-phonics go the 86 tube is notorious for such.

I'm wondering if the 12ax7 should be replaced with a 12au7 and if the 12ax7 was substituted in error @  one point and then remained.

DeKay

Not certain if it’s OK to swap 12au7 for 12ax7 in the event your unit has been modified.

Maybe someone here knows.

My only familiarity with 86’s is from re-tubing a couple of vintage Vox guitar amps for a neighbor.

It seemed that he went through 86’s quite often as he had accumulated lots of duds.

I also recall 86’s with shiny/sparkling plates and others with normal dull plates, but don’t recall particular brands (other than the shiny Telefunken I had on hand).

Have you tried contacting the designer of the preamp?

Anyway, what type of noise are you experiencing (gently tapping on the unit will tell you if it’s microphonic)?

If this is it, then gently tapping on either/both tubes will tell you which one (or both).

DeKay