Blue Box is back! Need help

[fusionbear]

I recently had a Super Reverb (Drip Edge) that had a strange issue, it would give you an octave down note when you would play on the low E between the 5th and 12th frets. Really pronounced effect. I found a .022 ceramic cap that would cause it and I replaced it. Well, the amp came back doing the same thing again.... I have no idea where in the circuit it is coming in. I got my signal generator fixed, so I will scope it tomorrow evening, but any tips would be greatly appreciated.

Thanks!

[Milkmansound]

check the 470R in the phase inverter.

[Stevem]

If sit the chassis outside the cabinet on a pillow or something does the issue still take place?

[Structo]

At first I was going to suggest it was a bad guitar string but since the owner experienced it too ...

Combo amp?

Sympathetic vibrations?

If it is the circuit, Milkman might have nailed it.
Could be a phasing issue at that frequency range.

Please let us know what it was.

[Phil_S]

Power tube swap? I've got a pair of Sovtek EL84's that do something like what you describe.

[fusionbear]

lead dress!!! Doh! The feeds to the power tubes were too long and looped back close to the PI. I cut about two inches off and re-routed. Viola! No more blue box...