Squeal on amp section

[jestaudio]

Bit of a funny one which may well me me doing something stupid, i have got the main power section on the quad 6l6 rockster complete and have been checking for correct voltage before carrying on, works fine with 2 tubes in inner or outer position but as soon as i put the full quad in i get a squeel, this is a known to be good matched quad, i havent got the inputs to the tubes connected to the phase inverter yet. Gut shot attached

[VacuumVoodoo]

Do I see shared gridstoppers? It may have something to do with your problem. I 'd rather have one for each tube.

[Structo]

Yes what is the grid and screen configuration you have there?

[jestaudio]

Yes what is the grid and screen configuration you have there?

Its a standard rockster layout with 2 extra tubes, the grid stoppers are shared as are the scren reisotrs, 2x200r , one screen for each pair of tubes, i think i may be picking up some interference, i connected the PI up last night then sent the coupling cap down to earth which shut the signal off, no noise at all then

[jestaudio]

It was the screen resistors, changed them from 1.5 to 2.2 k and added one on each tube, problem solved, one nice quiet power section also a a lesson for me to remeber

[ChrisM]

Might want to increase those screen grid resistors power handling capabilities.

[jestaudio]

Might want to increase those screen grid resistors power handling capabilities.

Already done, 3 watt metal as opposed to the original 2 watt carbon film, i did consider some old carbon comps i had in the right value but reckon they are wasted as screens