The amplifier
As a new owner of a Fender Dual Showman red knob reverb amplifier head, I set out to get a footswitch for my prize. The Fender “The Twin” of that period was almost exactly the same as the Dual Showman head (only MUCH heavier with its compliment of speakers.) After talking to about 20 sources including Fender and exhaustive searches on the Internet, I had gotten a handful of answers, but most were different; mostly debate about whether it called for a one or two switch foot-pedal or not. If you try looking it up, much of the data indicates the amp should have a single switch footswitch to just control the channels. There were not many made in this era that had reverb, but I happened to own one. So after getting nowhere asking around, I grabbed the schematics from a Fender “The Twin” amp and what I found did not surprise me in the least.