Can just one half (triode) of a 12AX7 be microphonic?

[dehughes]

I'm not sure if this is possible... I just wired in the other triode of V1 on my AC30-ish build so that both triodes are running in parallel (tinkering...trying to fatten things up just a bit), and after wiring in the other side I noticed that there is a very present hisssssssssssssssss once that channel is used (the amp has an EF86 side, too...). This hiss wasn't present in any form before I added the other triode, so to test things out I turned the amp up fully and tapped on V1 with a chopstick to see....and sure enough, there was a funky, flatty, ringy noise that ensued after the tapping. This didn't happen before, as I thoroughly checked all the preamp tubes for microphonics when the amp was "finished" (r.e., before I started tinkering...).

So, it seems that the other half of my new Tung Sol 12AX7 is microphonic, whereas the first half is dead quiet. Is this possible....does this make sense, or does it sound like I'm missing something...

[Dai H.]

yes, it's nothing out of the ordinary

[UR12]

It could happen but I would think that the added gain is causing the hiss and with the added gain the tube is probably a little more suseptable to microphonics that you were'nt hearing before with less gain.

[dehughes]

It could happen but I would think that the added gain is causing the hiss and with the added gain the tube is probably a little more suseptable to microphonics that you were'nt hearing before with less gain.

I thought this might be the case, so I switched V1 and V2 (both Tung Sols....) to see if that would make a difference. The switch did make a differnece, though the hiss is still there somewhat. With the noisy 12AX7 in the cathode follower slot I've noticed that it is less prone to microphonic noise... I'll try running completely different tubes in there tomorrow...

[dehughes]

yes, it's nothing out of the ordinary

Cool. I thought so...