Super Reverb continuing problem

[fusionbear]

Hello gents. I hope you can help me as I am at my wits end with this problem.

Amp: 68' Drip Edge Super Reverb

Problem described: When plugged into the vibrato channel, at about half way on the volume, you get an octave down ghosting when playing the e string from the 5th fret to the 10th fret. Does not occur on the Normal Channel. It did this before I did a full cap job.

What I have done: Replaced all electrolytics, replaced all resistors in the PI, Vibrato channel plates, reverb plates, .001 feed to PI, lead dress. I thought it was gone. I tested it thoroughly on my bench, but my customer let me know its back. Also, I replaced all tubes and played it through a different cab. My customer plays a Tele.

Help!

[Stevem]

Untill you hear it again for yourself do not assume that the customer is correct, or that it's the same problem! Please report back when you have it in front of you and have played it yourself!

[pdf64]

Yes, I'd look to see if a sig gen could be used to provoke the octaving.
If so, then separate the amp chassis from the cab to see if it's vibration induced.
Ear plugs and an empty house may be needed.

[Teleguy61]

Make sure it happens with your guitar or signal source.
A poorly set up Tele can sound pretty odd on the low E in that range.

[vibratoking]

I've seen this on quite a few amps. Usually a cold joint. I normally reflow all the joints and the problem disappears. Every now and then, it turns out to be mechanical...chassis rubbing on cab or cab vibrating. But you already heard the problem with an external speaker so I guess that's not the problem in this case.

[Richie]

I agree, a guitar with the pickup adjustment set wrong can cause weird out of tune notes and ghost notes, among other things.

So, it could be his guitar and not the amp. If it is the amp, you might go over the ground connections on that second channel. make sure they are clean to the chassis.

[Stevem]

Like posted your customer could have his pickups too close to the strings!

[vibratoking]

The stratitis proposal doesn't seem to fit with the symptom since the problem only occurs in the vibrato channel. If it is stratitis, then it would occur on all channels and it would occur without the guitar plugged in at all.

[rfgordon]

The vibrato channel has a lot of grid lead from the tone caps to the tone pots. This makes these amps subject to parasitic oscillation, aka Fenderitis.

An easy fix to try is to simply move the tone caps from the board to the pot tabs. It's completely reversible. I've eliminated odd noises from several Fenders this way.

[Stevem]

Well since the vibrato channel has the extra gain stage in V4, it's there that I would look for osscilation issues like two wires that carry signal that has gone thru 3 gain stages running too close or parallel with each other or instead of two wires it could be a coupling cap installed the wrong way next to such a wire.