I keep a couple of generic brute force power supplies around to use with my homebrew projects. This one grew out of a much modified and cannibalized WRL transmitter that I found at a swapmeet several years ago. From the back, on the right side is the high voltage section including transformer, choke, filter capacitor and rectifier tube. It will easily deliver the 500 VDC at about 200mA that I need for this project. On the left side is the bias supply. This section has a VR-90 with a pot across it. The exact bias voltage is set and then left alone. The six foot cable shown will plug into an octal socket on the back of the 815 transmitter.