noise peak at 300hz on tube pre?

[kambo]

i start getting this weird noise at 300hz on tube pre... i swapped the tubes...
so, one of the tubes is causing the noise for sure...

what kind a syndrome is that... is tube getting old!
did i apply too much HT voltage, heater voltage ?



thanks

 

[rock soderstrom]

Hi, it could be some kind of microphony.  Can. you change the behavior when you touch/ damp the tube?

 

[kambo]

yeap, super microphonic, i can make the graph move by clicking my touchpad  ;D

 

[rock soderstrom]

Lol, a preamp with a build in microphone. Very handy!  ;D

 

[kambo]

i have been trying to build one, couldnt be happier  8)