OK to use a Microphonic Tube in PI Spot?

[KillTone]

Just what the the title says...I have a really nice Sylvania 5751 that cannot be in V1 without squealing.

I know they are good in the PI too but just curious on opinions in using a know microphonic tube there.

 

[Mattfig]

Interesting question...At first I wanted to say no...But since microphonics don't come into play with inversion I guess it should be fine...

Although let's wait for a pro to confirm...I'm almost always wrong...

 

[m0jo]

Microphonics are a sign of wear and tear .. meaning it's probably on the way out slowly.
Also a PI doesn't do that much to tone AFAIK (could be wrong), so then it wouldn't be very useful to do anyways. And since it's "worn" it probably doesn't perform like a balanced tube people often go for for PI tubes.

I don't know, it should be fine and if it sounds good .. cool. But I don't trust microphonic tubes

 

[kc2eeb]

If the tube is microphonic in a combo amp, it may not actually be.

 

[m0jo]

If the tube is microphonic in a combo amp, it may not actually be.

That's a whole different story

 

[Mattfig]

See? I don't know *****..Strangely, I've never owned a combo guitar amp...I'm curious as to the different usage of triodes here...

 

[Daryl]

If the tube is microphonic in a combo amp, it may not actually be.

Is that because of the actual mechanical vibration in a combo amp?

 

[Mattfig]

Flux Capacitor, I believe...

 

[kc2eeb]

In a word, yes. You can get ultrasonic oscillations, feedback, etc.
even feedback from the reverb pan.
One of the reasons I converted my RM50 combo to a RM50 head.
The same tube that appeared microphonic in the combo configuration
was not in the head.
Also, In most speakers, the actual frame of the speaker is not grounded
to the amp chassis. Sometimes grounding the speaker frame to the amp can stop feedback.
Try putting the microphonic back in the amp, turn up the volume until it
starts to squeal, and put your hand around the tube, not directly on it.
See if that changes anything.

 

[kc2eeb]

Sometimes, all it takes is a really good flux.

 

[KillTone]

Thanks for all the answers guys. I will probably give it a shot when I have time for some critical listening. Right now I have a balanced gold pin TunSol in there and the amp sounds great so I am not highly motivated to make a lot of changes.