Hiss in fender amps

[shocki]

I have a similar in a maintenance thread already. But I would like to talk about this in general. Right now I have a blackface bassmann which has alot of hiss. It got a bit better when I changed the mixer resistors and the plate resistors.
But still there is quite a lot of hiss. Already when Vol is turned down. But of course it gets way louder when you turn it up. When just using the normal channel its OK. But if I add the Bass channel (which I voiced similar to the normal channel) there is even more hiss.

Other amps I have and had were Soldano, Badger 18, Marshall JMP. None of those had hiss problems. I also have a Deluxe Reverb which has hiss problems (just using the normal channel) but not as bad as the Bassman. Is there something in those Fender amps that generates this hiss? Is this something in the circuit and can anything be done to cure this?

I am not talking about hum in this case (!)
Thanks alot.

[shocki]

OK. I now pretty much replaced everything with carbon film resistors and the noise got a lot better. Not just the plate resistors. I needed to change almost anything. Also the slope resistors and other resistors in the path. Hard to say which resistors really improved what. I listened after each resistor replacement but could not tell a huge difference. But in the end the amp is alot quiter. Just a little bit of hum left now. Maybe I will replace the bias cap.

BTW. What I noticed is that all plate resistors shifted to 120k. I think the 120k should give me a bit more gain. Maybe I will use 120k resistors to get that sound

[Justin Thomas]

Glad you sorted it all out - I don't think there's anything inherently hissy about these piggies at all - it's not a "high gain" design. I think it's gonna make funny noises cuz it's old and prolly needs some TLC! It IS almost 50 years old... one other thing - were your preamp tubes selected for low noise? And if they're a "high gain" type, they can add some hiss...

Justin

[Enzo]

Agree, anything that pertains to your Bassman will apply to just about any other Fender amp. The circuits are all pretty much the same under the skin.