John’s Indispensable Power Supply

I use this almost every day despite it being 50 years old. The 10-turn pot with digital readout can be set to a precision of 0.1V on DC. and it is usually spot on. The positive is good from 0 - 40V and often can give 10A. The negative less so.

You must turn off the power when switching between DC and AC. The AC is supplied from a motor-driven Variac and has a tendency to hunt. 

Only the positive output is current-limited.

It has huge heat sinks on the back although the Variacs are in a separate feedback loop which keeps the voltage drop across the pass transistors constant.