H754 +20V, -5V Regulator
The H754 +20V, -5V Regulator is one of the DEC standard modular regulators. It can produce an output current of up to 8A at an output voltage of +20V, and up to 1A at -5V. (Technically, the two trade off with each other, so if there is less +20V being drawn, more -5V can be drawn, up to a maximum of 8A.) It has over-current and over-voltage detection and protection.
It was a switching power supply, one of the earliest; however, the basic concept was somewhat different from later supplies of this type. It takes as input AC at a voltage of 20V-30V, runs it through a diode bridge and filter capacitor to convert it to DC. That is then used to produce a 25V output (+20V to -5V); a pair of shunt voltage regulators then produce the two output voltages.
It took its AC input on pins 7 and 8; the +20V output was on pin 5, the -5V on pin 3, and the ground return on pin 2. Pins 1, 4 and 6 were not connected.