Got a microphonic tube! Which one is it?

[Clone Funk]

I need to know how to tell which tube is microphonic. Is there a trick to finding out? All I know is when I turn on my amp, after a few seconds I hear a beeeeeeeeeeep. How can I fix this?

[That90'sGuy]

What you can do to hear if a tube is microphonic is pretty simple. Run the amp, get out a pencil and tap on the tube. If it echoes, you know it's microphonic.

[proxy]

Tap it, you should hear it through the amp when you tap it, however at this point you shuld prolly replace them all.

[proxy]

jinx

[Wattage]

First you can try tapping the pre-amp tubes with the eraser end of a pencil and see which one rings, that would be the culprit. You might switch their positions around and see if that helps.

[Clone Funk]

Ok, I tried it and one of the tubes makes more of a squealing every time I tap it, and as far as the other ones, they all kinda sound hollow so I can't tell. Can I just replace the one that squeals more when I tap it or what?

[proxy]

I honestly would replace them all, but yes you could.

[That90'sGuy]

If it squeals, then you know its bad. As far as replacing them goes, I guess you'll have to use your own judgement on that.

[AmpliFIRE]

They should sound hollow...not squeal. Replace that mofo with a new one!

[lastwinj]

you can also you use your fingernail. no need to get out the pencil.

germ

[That90'sGuy]

Aha, never realized that... good call!