Problem with my Ampeg V2

[Foxfire]

i think the second thing i did once i found the issue was to pull the bypass cap in the FBL with big hopes, but alas the cap is good. i'm all but certain that V3's cathode network is solid. it's got the 1.9v it should and the 2 resistors checkout. the voltages for V4 are good but i'll take a better look at them. i am also going to order new sockets for the power tubes. i retentioned them but i can hear noise when i twist the tubes with a "reasonable" amount of force. until then i'll make sure V4 is good...

and i never get tired of saying this, Thanks again...

[Chuck H]

Welcome. Keep testing and looking within the feedback loop. Something is hinky or else ALL those amps do it under similar operating conditions.

[Foxfire]

ok so i as a test bumped up the feedback resistor to 10KR from the factory 4.7KR and the ugly seems to be gone. my test cab in the basement isn't the most solid cab out there and it seems like everything in my basement is just itching to rattle, so i can't say definitively until i bring it up and run it through my main cab but i can say that with the 10KR feedback resistor i don't hear the noise that i was hearing with the 4.7KR.

i'm assuming that bumping up the value is just a band aid rather than a fix unless,

a. 4.7KR was always too low or was borderline too low, i.e. it worked most of the time in most of the amps

b. 4.7kR becomes too low as parts age or wall voltage goes up

c. some other factor/variable i can't think of/don't know

So if it is a just band aid, then would it have to be true that the noise/distortion is in fact still there with the NFB removed but is at such a low volume that it can't be heard until it is fed back in to the circuit through the NFB loop and then amplified?


Update, 10K wasn't enough so i jumped up to 22K and i will say that the noise has lessened considerably but is still there.

[Foxfire]

well after spending another 4-5 hours on it yesterday i feel like i'm just wasting our time. whatever is going on will need to be scoped to be found. i just don't think that i'm gonna find it with my little audio probe given my limited knowledge. it seems as though i'm disproving everything as quickly as i "prove" it...