Mesa 5:25 "ghost note"

[Danglin' Fury]

Got a Mesa 5:25 on the bench. Dude says it has a ghost note anytime he hits a B-note. I've played it today and, yes, it does in fact have this issue. sounds almost like it has an octaver pedal on it. It is not really super loud compared to the original note but annoying nonetheless. Funny thing is, he sent it to Mesa for this problem. Twice. And both times they basically told him he was crazy and there was nothing wrong with his amp. Does anybody have any idea where to look on this guy? I've been told to look at the last cap in the B+ before the pre-amp and Somebody else said I should cut in half the two "output" caps right after the phase inverter. Any suggestions? Thanks for looking.

-Shawn-

P.S. I've already tried a different speaker. still does it.

[jmaf]

Ghost notes are normally a symptom of bad power supply capacitors. The power supply is getting modulated and you get the ugly overtones.

The B note and its even harmonics are the closest to 60 and 120 Hz, that's probably why you hear the beating harder on B's.

[Chuck H]

jmaf is right. If it's B that's giving you the ghost note it's most likely a filter problem. This usually happens on the B note when there isn't enough ripple control. I know Mesa used to use Sprague Atoms. I don't know if they still do but I've decided to switch from Atoms to something else because they've been performing so poorly for me lately.

I'd say try the old hack job fix of paralleling another filter across the main filter. I find that when you hit el84's hard you need about 80uf on the main filter to squash ghost notes. There's no tube rectifier on that amp so there's no upper limit to what value the main filter can be.

[g1]

And don't forget any electrolytics in the bias supply, they count as filter caps too!

[Danglin' Fury]

Call me Peter Venkman because I'm a fuc#ing Ghostbuster! It was the last power supply cap (C54 on the schemmie). That cap had some "connection issues" also, C52 and C53, the caps right before it on the schematic are Nichicon caps. C54 was a CKEM (???) It looks like somebody was in that amp before and changed it out. Well when, or if, they did, they did a hack job. One of the pads was completely gone and it was barely hanging on to a trace on the + side. Well, I repaired the hack job and voila! No more "ghost notes". Thanks fellas for pointing me in the right direction. I also fixed the channel switching latency in that thing if anybody is interested in how that was done.

[Chuck H]

Peter Venkman
Peter Venkman

(huh huh... His name is peter.)