Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ledvedder on November 17, 2023, 11:02:32 pm
-
Hi everyone, it's been a while. I finished up an Express build tonight. When testing it, I noticed this strange noise while notes are decaying. Any thoughts what to check?
https://on.soundcloud.com/WX9rH
-
Have you tried different tubes? Is this a combo Trainwreck or a head? If a combo, does it still do this when outside the cabinet? I'd check soldering. Have you chopsticked the amp? Have you tried a different speaker?
Do you have a passive effects loop in the mix? Did your soundclip involve any pedals or were you plugged straight in?
Can you post hi-rez photos of the chassis interior?
You might do a search on the forum about "enhance cap" which is a smoothing cap across on of the LTPI plate resistors.
With respect, Tubenit
-
It's a head. No effects loop. I did chopstick everything, and it all seemed fine. I realized that I had it biased pretty cold. After bumping it up to about 42ma, that noise went away.
-
It's a head. No effects loop. I did chopstick everything, and it all seemed fine. I realized that I had it biased pretty cold. After bumping it up to about 42ma, that noise went away.
42 ma at what plate volts ?
I bias close to 60% power dissipation not 70
-
396v.
-
The enhance cap is a 220pF cap across the 82k resistor? I'll have to give that a try.
-
Yes, 120p-220p range across the 82k LTPI plate resistor. Glad you got it resolved!
With respect, Tubenit