The way I draw a schematic from a pcb is to scan or photograph the foil side, flip it mirror image in the computer, print it on paper and draw the components on.
Works great for single sided boards. Double sided is a little more trouble. SMD? Forget it!

If you can post photos of both sides of the circuit board I can do it for you.

The last few Peaveys of this vintage that I've seen had either shorted or open main filter capacitors.

This is the amplifier chip used in the Mini3. Note the physical size - 1.5mm square!

A little further searching and, Bingo!

This is not exactly what you're looking for, but does show the footswitch to preamp wiring.

Please post photos of the circuit board, both sides.

Are you sure the 47K resistor at the input is correct? 470K or 1M would be better, and change the input capacitor from .22 to .022.

If you replace the transformer with a 17V version, you will have to upgrade some other components.
Change the 1N4002s to 1N5404, Change the 2200 uF caps to 3300/35V, Change the 2 100Ω feeding the zeners
to 220Ω/2W.

Here is a way to connect the reverb module. You have two choices for the input.

Here is the schematic

Hi Julio

Can you post some better photos of the circuit board, both sides?

Re-check the transistor area. something is wrong.

I can draw a schematic of this board if you take another photo of the component side with the heatsink removed and another photo of the foil side with the white material removed
And if you can clean the foil side with solvent and an old toothbrush or whatever, it would help

The pot is 1M, the taper is 10A which is a version of Audio Taper. Here's a chart of tapers for Alpha pots.

Here is the B-4 Owners Manual and Schematic. Maybe similar in some way.

Here it is: