I'm looking for a reference to a high voltage screen power supply for an RF high power amplifier. I'd like a shunt regulated supply so that it has a low impedance and preferrable variable voltage around 300 to 400 volts or so. I know that basic regulators can be made using VR tubes but I'm looking for something more robust and with some adjustment capability. I'm sure that I've seen one in some magazine in the past but my memory fails me. Anyone remember seeing one and where?