Grounding - it matters, right?

[Justin Thomas]

Hi Everyone and Happy New Year!

Have a Bassman 50 w. MV that I had to gut & rebuild, so I guess it's a clone?

Playing it loud last night, I noticed loud buzzing and humming and light oscillations. Hmmm, that wasn't there before... All but 2 controls affect it, pulling ALL preamp tubes fixed it, at one point poking dang near EVERY wire in it either worsened or silenced it. Get it quiet, twiddle a knob, it's back. I noticed the ground wire that I have from the PI to the MV pot, they have from PI to V3 cathode grounds. Make change and voila - no noise! I'm a believer - ground scheme and layout matter! I'll fool with it more today, but I'm 95% sure it's done.

Was wondering about a paper layout diagram because I seem to have an extra eyelet leftover? It's pretty busy in that area in the photos I found, can't see what's happening... Found one for Bassman Ten, figure they musta made one for this piggy...

Can't post pics unless you want me to try my really old camera phone to online album...

So, my question is, does that make any sense, can the location of one ground cause that?

Justin

[R.G.]

So, my question is, does that make any sense, can the location of one ground cause that?

Yes. Both theoretically, and as you've proven, in practice.

[Justin Thomas]

Thanks R.G.,

I read up some on grounding, primarily Merlin, and he said we should think in terms of current, not just voltage. I have a Spitfire clone that had some of the same problems (oscillations) which is now fixed (grounds/lead dress) and a screaming monster! I'll keep going through your debugging page - this Bassman is lacking in the clean area, but it's also a MV & the 1975 catalog says it can be dialed in for "any desired amount of distortion." Which is not much, cuz the distortion don't sound great. I can't tell if it's by design or other problems. So I'll do what I can with it and then sell it. It's a great punk amp!

It's good to have the MEF around still, best place on the web!

Justin