Can someone please explain this contraption?

[Leo_Gnardo]

I found a few more little weird things on this amp last night...not too weird but I'm wondering why someone did this.

There were 250pf silver mica caps going from grid to ground (pin 1) on each output tube. In the process of removing these things I noticed a gigantic blob of solder on pin 8 of one of the tube sockets. While removing this blob the pin just fell off. Broken. Pin 8 on this tube socket was held together with solder. Ugh. New socket ordered.

Also someone switched the .022 PI coupling caps to .01. Don't know what that's all about. Make the amp brighter?

And finally there is a .022 cap to ground off the ground side of the input jacks. I'm guessing this is to bleed off RF interference.

The 250 pF silver micas, probably an attempt to squelch ultrasonic oscillation. Fender did it factory installed in some of their black & silver-face amps 60's & 70's, much larger caps 0.02 uF IIRC.

Reducing value of coupling caps would tend to block lower frequencies but going from 0.022 to 0.01, just marginally.

About that last 0.022 uF I can't imagine. Someone else can pitch an answer for that I'm sure. Or maybe not?

[Greg_L]

The 250 pF silver micas, probably an attempt to squelch ultrasonic oscillation. Fender did it factory installed in some of their black & silver-face amps 60's & 70's, much larger caps 0.02 uF IIRC.

Reducing value of coupling caps would tend to block lower frequencies but going from 0.022 to 0.01, just marginally.

About that last 0.022 uF I can't imagine. Someone else can pitch an answer for that I'm sure. Or maybe not?

Yeah I'm just going to replace that broken tube socket and put it back to stock schematic-correct values. I'll go from there. These are pretty good amps IMO. I really doubt all these shenanigans are necessary but we'll see.

I will be leaving the elevated heater ground reference thingamajig though.

[g1]

And finally there is a .022 cap to ground off the ground side of the input jacks. I'm guessing this is to bleed off RF interference.

Attaching schematic (non-FX loop version) for reference. Don't see any such cap there. Agree about RF suppression, or possibly someone was trying to cure an oscillation issue like Leo mentioned with regard to the silver mica caps added at the power tube grids.

[Greg_L]

Attaching schematic (non-FX loop version) for reference. Don't see any such cap there. Agree about RF suppression, or possibly someone was trying to cure an oscillation issue like Leo mentioned with regard to the silver mica caps added at the power tube grids.

That's the more modern "Randy Rhoads" model schematic. The one I'm dealing with is an older standard Super Lead and has a slightly different layout.

[g1]

That's the more modern "Randy Rhoads" model schematic. The one I'm dealing with is an older standard Super Lead and has a slightly different layout.

pg.4 of attached includes the older re-issue power amp section

[Greg_L]

pg.4 of attached includes the older re-issue power amp section

Yup that's the one.

[Greg_L]

Well this thing seems to have come out really nice. I put all of the weirdness back to stock. Works great, sounds great.

I did leave the elevated heaters, and that is indeed what that contraption is after further poking and prodding. The 6.3vac heater voltage is riding on top of 50vdc. The amp is very quiet at idle and stable. So good to go rock and roll.