Hot Rod deluxe motorboating in drive channel

[sbluestubes]

I have a problem with the drive channel on the hot rod deluxe motor boating in both the drive and more drive modes and it is affected by the bass control. The clean channel is not affected since V1 and V2 share the same filter cap I am a bit puzzled anyone run into this ?

[rriddy]

hot rod deluxe motor boating

Did you ever find a cure for this? I have one doing the same thing.

[pdf64]

I guess that C36 22uF 500V, the cap which bypasses power supply node X that feeds all the pre-amp, is the prime suspect. Tack a good one across it and see if that stops the fault.
http://www.fender.com/support/amp_sc..._Schematic.pdf

[xtian]

Old thread, but just wanted to add my +1. HRD on the bench making motorboating oscillation on Drive channel only, and period of oscillation decreases (and pitch drops) as Drive control is turned up. As suggested, I clipped in a new 22uF cap across C36, and this made the problem vanish.

[Jazz P Bass]

Not everyday you get a 'it's XXX' repair.

C36 is used as a decoupling capacitor.


If you scope the + side of the cap (a bad one) you can see the Drive signal riding on it.
Not good.

A good cap will prevent this.