a little help needed

[jestaudio]

Hi folks
ever get the feeling you should,nt have started a project, I,ve got it now lol.
The amp I have is based around a Roost, only 50 made, got to be worth saving,
The issue I have at the moment is distortion in the preamp and low output, voltages all look ok except around the PI, I,m around 60v down on one leg, I should around 280/271v, I have 279/ 190, the dropping resistors are specked at 82k each and reading around 84/85k, the master volume is pre PI and similar to a 36w tmb with a cathode follower arrangement,

Every time I turn around with this amp another problem crops up, its also worth mentioning there is a little buzz within the preamp, sounds like 55hertz interference, I am on a clean circuit and have no interference in any other amp

[ampfab]

have you swapped tubes to see if that affected the voltages?

[jestaudio]

have you swapped tubes to see if that affected the voltages?

yep, tried 2 fairly well balance sovteks, best I could get is a 240/200, still a fair way out

[ampfab]

Standard LTP?

[jestaudio]

Standard LTP?

Heres the schematic

[ampfab]

"82k Dropping resistors on each leg" are you referring to the PI plate resistors? Where are you measuring voltage? Schematic available?

[jestaudio]

"82k Dropping resistors on each leg" are you referring to the PI plate resistors? Where are you measuring voltage? Schematic available?

Schematic attached on previous post

[ampfab]

If your voltage is low, that would mean that too much current is flowing. Both triodes of the PI share cathode resistors. So, I wouldn't think that would cause uneven current flow. I would would disconnect the coupling caps from the output of the PI and recheck voltages. That extra current has to be going somewhere.

[jestaudio]

If your voltage is low, that would mean that too much current is flowing. Both triodes of the PI share cathode resistors. So, I wouldn't think that would cause uneven current flow. I would would disconnect the coupling caps from the output of the PI and recheck voltages. That extra current has to be going somewhere.

That's one problem sorted, bad connection from the PI to the output tubes, now trying to track down the buzz in the preamp, sounds almost like a unshielded cable or earth loop

[Structo]

Check your grounds and solder joints.

[jestaudio]

Check your grounds and solder joints.

all checked, nothing obvious apart from pinning the buzz down the somewhere in the reverb circuit, there are a few old electrolytic caps used as bypass caps , trying to nail weather the buzz is getting in before the spring unit or in the recovery side

[ampfab]

Make sure the reverb spring is not plugged in backwards. Preamp tubes can often cause buzzes or hums. If you haven't already, try swapping tubes around.

[jestaudio]

Make sure the reverb spring is not plugged in backwards. Preamp tubes can often cause buzzes or hums. If you haven't already, try swapping tubes around.

yep done that one before lol, all good on that side, tubes are all good, going to be something stupid lol, i'll give it a break for a few days while I get to know my newly acquired Carvin V33