Tube amp, hums alot. Microphonics?

[jzono1]

I got major problems with hum on my tube amp. First and worst - enormous ground loop problems if I use my computer as the source. Second, and a show-stopper anyway - microphonics. Atleast that's what I think the second one is.

It's loud enough to be noticeable under quiet passages. With the volume knob at 0% it's loudest, declines gradually up to 100%, which is where I prefer to keep it, since I have volume control on my sources anyway. Say about halfway turned down the hum drowns the music.

With the hum, I can also hear the tubes themselves vibrate at that exact same frequency. Loudness of the vibration correlates to the hum hear through my headphones.

Microphonics, right? Sounds like the first stage is where it happens. The amp is a twostage darling 6j4/1626 which I built myself.

 

[Lil' Knight]

Did you try using some tube dampers?

 

[jzono1]

Haven't got any of these around. What tube dampeners are reccomended?

However, I remembered that I had a spare tube of another brand lying around after a debugging session during the build process.

The spare is a plain GE 6j4, and running it with one of the sylvanias greatly reduces hum in that channel while the sylvania's channel hums a bit less than with just sylvanias.