Peavey Butcher - What mod is this???

[liamfossaluzza]

Hello. not really good at doing anything with amp electronics except simple mods with clear instructions, or small repairs. Basically I got this old school peavey butcher and I would like to know what the previous owner did to this. It looks like they connected something from the middle preamp tube to r20 ideas??

Schematic: https://irationaudio.com/2015/09/25/peavey-butcher/

[g1]

It could be a factory installed part. What makes you think it is a mod the previous owner installed?

[liamfossaluzza]

I've seen a few other photos of people's butchers and none of them have this and also, it doesn't show it on the schematic

[g1]

it doesn't show it on the schematic

So where exactly would it be located on the schematic? Which tube is that, V6?

[Pixel]

So where exactly would it be located on the schematic? Which tube is that, V6?

B+ bypass?

[Enzo]

PIn 3 to ground.

[Pixel]

PIn 3 to ground.

Yeah thats it! I was looking at the wrong trace.

[Pedro Vecino]

It is a cathode follower circuit. It is connected between pin 7 (connected to pin 1) and ground. It must be V6.

[glebert]

PIn 3 to ground.

I don't think it is to ground, I think it is to the other side of R20 (which is almost ground since R20 is only 47 ohms). If you look at the layout the P2A node on the other side of R20 is "true" ground.

I can't make out the value for sure, seems a little big to be just for stability, maybe a tone-tamer to drop some high frequecies off?

[Enzo]

SO look closer, where does that other end of the 47 ohm connect? Preamp ground. Note the line goes straight to chassis down through P1A/B. Yes, both ends of the 47 ohm are grounds. Peavey has multiple grounds in this circuit, like they often do, and the resistor keeps them linked.

I did say pin 3 didn't I? I meant pin 7.

[glebert]

SO look closer, where does that other end of the 47 ohm connect? Preamp ground. Note the line goes straight to chassis down through P1A/B. Yes, both ends of the 47 ohm are grounds. Peavey has multiple grounds in this circuit, like they often do, and the resistor keeps them linked.
.

I see that now.

[g1]

So it's from the CF plate/grid (V6 pin1 and 7) to ground. Appears to be .047uF ? from the picture but I can't be sure.
Some complain about these amps being bright/harsh sounding so I would think this mod attempts to take a bit of the fizz out.

[The Dude]

Yes, or maybe to get rid of oscillation.

[Pedro Vecino]

From what I can interpret it appears to be a 470pF / 3KV ceramic.