fender 568 trouble

[tonequest]

Howdy : Wondering if anyone might help with a problem I have with an early 70s super reverb? When i add a little overdrive to the frontend i get some off key harmonies following certain notes.Just changed the filter caps tried other tubes,rectifier and preamp tubes.The overdrive was fine in my other super. Thanks for the help.

[Cygnus X1]

Ghost notes?

Check your lead dress, and your cap values.

[rfgordon]

It's very common for BF and SF Fenders to develop parasitic oscillations that can sound like icky, out of tune distortion riding on the notes. The main reason for this is the huge length of the grid wires in Fenders. (you probably already know this, but the lead between the plate and the coupling cap is the plate wire, and after the cap it's considered grid wire.)

The best solution for this is to take the tone filter network off of the circuit board (the three caps and the 100k resistor). Re-assemble them and attach the caps directly to the proper tabs on the tone pots. Glue the caps to the backs of the pots with a wee bit o' silicone squeeze. Then simply connect the input location (junction of the 250 pF cap and 100K R) to the eyelet there the lead coming from the preamp plate attaches.

I've done this in a couple of Fenders (Pro Reverbs and Supers), and trust me--it works. It's also described in one of Gerald Weber's books.

[tonequest]

Thanks for the input rfgordon & cygnus. The lead wires are ok and I'm still cap checking.but. common sense tells me it's somewhere else because it's a global problem{both channels}I'll keep lookin.

[M Fowler]

On working with the Fender Tremolux, Bassman, and Super reverb amps I have owned, that type of sound your hearing I usually found with old filter caps. I would also change some of the other caps in the circuits as well.

Mark

[Structo]

What guitar is this doing this with and is it a strat.

A peculiarity of strats is a phenomenon called stratitus.

It has to do with having the single coil pickups too close to the strings and you get these weird harmonic overtones that sound like crap.

If it isn't the guitar, sorry I don't know.

[austinb]

Ghost notes are out of phase signals that are summed back in with the primary signal. First is this ghost note always the same frequency or does it follow the primary sort of? If the ghost is 60hz or 120hz then is a filter cap. if its 180 degrees out of phase its the primary of output transformer leads are backwards and someone changed the feedback resistor to tame it down. Some part of the circuit is on verge of oscillating and amplitude enables it such as a microphonic tube. Also check for dc on grids caused by leaky coupling caps. These are what comes to mind to check.