This is a little info about the boost switch I added to my Prairie Dawg amp.
The amp is basically a single channel Fender blackface with SRPP driven reverb. With this amp I wanted to get a blackface sound but also a blackface plus a little more sound.
I tried lifting the tone stack from ground and thought that sounded terrible. Switching in a fixed resistor between the tone stack and ground was better but still not quite there. I also tried switching in a bigger cap parallel with the 250pF treble cap in the tone stack. This was ok but still not quite it.
After messing around with these ideas and I finally remembered the Texas Tea control in the Kendrick Climax. You can see the schematic here.
On the first page you can see there is a .01 coupling cap and 3M pot that bypasses the tone stack. I used that concept as the basis for this boost switch. I reduced the coupling cap to .0047 just because I thought it sounded better. I also replaced the pot with a 470k resistor. I actually used two 470k resistors, one with a 500pF bypass cap, and a On/Off/On switch.
With the switch i the middle position there is no boost and it’s the standard tone stack.
In the bottom position there is the .0047 cap and 470k resistor bypassing the tone stack for a nice boost. In the top position there is also the .0047 cap and 470k resistor but the resistor is bypassed with a 500pF cap. This forms a treble peaking circuit like in a Marshall and adds a high end emphasis to the boost. This works great with humbuckers.