Don't let the 5Vac rectifier winding to go to waste.
The circuit is a simple voltage doubler that converts the 5Vac into 12Vdc for the power amplifier's frontend circuitry. It is not that big a deal, but once you have point-to-point wired a few of them, you begin to long for a tight little PCB. The parts are first rate (Panasonic FM series 1kµF and Panasonic 10kµF 105° capacitors, ultra-fast MUR410G rectifiers, and four sets of standoffs). The American made PCB is extra thick (0.094") with 2oz copper traces and is 2 inches square. Kit includes user guide.