Channel-Switching Preamp Mod for AB165 Fender Bassman

A PDF schematic of this mod is here....

The guitar used for these sound samples is a Lone Star Strat modded with Bill Lawrence L280/L280/L290 "single coil" style noise-cancelling pickups and 6 month old strings. The speaker is one of a pair of Mesa-Boogie MS-12 150 Watt "Black Shadow" speakers--the original type Black Shadow from the early '80s. These speakers reside in a pair of homebuilt 1x12" rear-ported cabinets. I recorded this with an AKG D3900 microphone right next to the speaker grille, using no EQ. The amp is tubed with EH EL34s, a Tung Sol 12AT7 in the PI, a JJ/Tesla ECC83S in the loop buffer/recovery slot, another ECC83S in the drive channel's second/third gain stages, and an old ('80s) EI 12AX7A in the input/CF stage.