Tube Hum / Rattle

[Big Tuna]

Hi Guys

I have an HT 20 Combo.

Zero volume, input jack not connected, and I get a slightly micro phonic hum.
If I tilt the amp slightly backwards OR push down slightly on the top, it disappears.

If I remove the back, it doesn't do it.

I am thinking some sort of micro phonics.

Any thoughts?

[toneseeker]

Hi Guys

I have an HT 20 Combo.

Zero volume, input jack not connected, and I get a slightly micro phonic hum.
If I tilt the amp slightly backwards OR push down slightly on the top, it disappears.

If I remove the back, it doesn't do it.

I am thinking some sort of micro phonics.

Any thoughts?

yes i would say one of the preamp tubes may be crook!

[TheDude]

If you have nothing plugged in the input and the master volume is turned down then I would strongly suggest that one of the output valves (EL34) is faulty.
Also regarding pre-amp valves - if it effects both channels then I suggest they are fine.

[Big Tuna]

Thanks Guys

I did open it up to have a look.
The spring clips seem to make it worse, it didn't do it when they were off.

I am thinking it is a power tube as well.

Problem is, if I get new ones, how to bias