Trainwreck Express weird note decay

[Ledvedder]

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

[tubenit]

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

[Ledvedder]

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.

[Latole]

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

[Ledvedder]

396v.

[Ledvedder]

The enhance cap is a 220pF cap across the 82k resistor? I'll have to give that a try.

[tubenit]

Yes, 120p-220p range across the 82k LTPI plate resistor.  Glad you got it resolved!


With respect, Tubenit