Noise problem in RedBear

[Pellepop]

Hi
I got a white nosie problem with my ReadBear MK 120. I have change both pre and power tubes. Using original new tubes from Russia/Ukraina. The amp makes this noise even with both pre and master volumes set to zero. What would be the next thing look for?
Most tankfull for an answer.

[ampgeek]

Welcome Pellepop!

Does it make the noise without the instrument cord plugged in?

If so, I would start by looking very closely at the input jack and the integrity of the ground connection at that point.

Good luck!
Dave O.

[Pellepop]

Tank you!
Yes it makes noise without cord in. And with the phase inverter tube removed as well. Its a noise that comes and goes randomly.

[xtian]

So if the noise happens with PI tube removed, that leaves power tubes. You said you tried new power tubes, so if they're not the problem, you'll need to look at the power tubes' screen resistors (looks like 470R 2W on the poor schematic attached) and the grid resistors (probably 1K).

If that fails, then filter caps?

Smarter guys here will chime in.

[Pellepop]

I´m most greatful for your answers!

[Structo]

[img1056]http://www.prowessamplifiers.com/projec ... d/RB_4.jpg[/img]


The amp is documented here.

http://www.prowessamplifiers.com/projects/Redbear/