Hiss in BF Bassman build

[EETStudent]

I have done much troubleshooting, but has anyone had any experience with hiss in a black face bassman? I generate hiss with in mine with the 3rd stage introduced. I bypassed it and the hiss was pretty much reduced, so I suspect something in that stage. Im using an old rca 6EU7 in that spot, so that could be the culprit. Ill do some more tests, but i didnt know if this was common or not.

[cminor9]

What kind of resistors are you using?

My 5E3 had all carbon comp resistors. I replaced the 68k stoppers, the 1M bright resistors, and the cathode resistors on all preamp tubes. Left the carbon comps everywhere else. No more hiss. I'd recommend that, assuming that your amp is working properly just with some hiss.

[EETStudent]

Yeh its working fine, just kinda hissy. and the controls jump up fairly early. maybe I need to cut down the signal in this stage.

[Amp Kat]

You did change the wiring on the 6EU7 right ? They aren't a direct replacement for a 12AX7. Are you talking about a hiss like the ocean or more of a buzz. Usually the case of hiss is either a bad connection or a wrong component value in the signal chain.

[EETStudent]

lol yeh I changed the wiring. The amp works fine and sounds terrific, and I just got rid of a third volume control i was using and the noise issue is much improved. With just two gain stages, the hiss is nearly removed completely. When I add the third it gets a little more prominent, but its definitely not overbearing so im not too worried about it.

[tubeswell]

Tried metal-film plate resistors?

[EETStudent]

yea Im using metal film resistors on the plates. The hiss seems to center around the 3rd stage. When bypassed, the signal is clean and sounds pretty nice. However, with the 3rd stage wired in, their is a lot of hiss and the volume controls respond rather quickly. As in the amp gets really 'loud' with the gain around 3 and MV around 3. Unfortunately the tone even better with the extra stage, but I dont take too well to noise. A noisy amp seems like a bad build, and i dont wanna be a bad builder

[cminor9]

What kind of resistors are you using?

My 5E3 had all carbon comp resistors. I replaced the 68k stoppers, the 1M bright resistors, and the cathode resistors on all preamp tubes. Left the carbon comps everywhere else. No more hiss. I'd recommend that, assuming that your amp is working properly just with some hiss.

I know someone else recommended metal film resistors and that they are already used in this build. That's what I was trying to do here in my first response. I just didn't insert the words "metal film resistors". I rewrote parts of the post and I guess lost the very essence of it. Dang it!

I know this is an old thread now, but I had to correct myself. It was just bugging me, looking like a tard and all. Now I still look like a tard, but at least less of one.

Anyhow, carry on.