MP-1 loud buzz

[j_weeks]

I just picked up another MP-1. The unit works fine for the first 1-2 minutes, then after it heats up i start to get a loud buzz/hum. I put new tubes in it and noticed that one of the tube sockets was slightly loose, but both tubes still light up when powered on. Has anyone experienced this problem before?? :???:

[j_weeks]

Heres a video of what the preamp is doing. https://www.youtube.com/watch?v=tAgtZCMz-UQ

[j_weeks]

Hell I think I found the problem. One of the caps looks shot.

[rnolan]

Mmm, it's not looking like a happy cappy, and you may well have located your problem (and hopefully that's all it is)

[MarshallJMP]

Yes seems to be shot,replace all 3 (black) caps while you're at it.

[j_weeks]

I replaced all 3 caps on the tube board (6.8 uF 450v) and she's back and running perfect. No more hum :banana:

[MarshallJMP]

Ok great to hear!!

[rnolan]

I replaced all 3 caps on the tube board (6.8 uF 450v) and she's back and running perfect. No more hum :banana:

[gb]

So by caps you mean capacitor?  And how do you know if they are stuffed by looking at them?

[j_weeks]

Correct gb. If a capacitor is swollen out on top, or busted open as in the case with my mp-1, it is an obvious sign that the capacitor is no longer viable. That is not always the case though, some bad capacitors show no signs.