Having seen more I'll make some other educated assumptions.
I think I was close with the back panel, allthough looking at the pic of the complete one the switches at the left on the back panel are not freq and duty, they look like they are just logic hi/lo from the output sockets, those switches probably just go through a logic gate to the output socket.
The 2 knobs on the left look they they are a + and - power supply using the lm317 and lm337, so maybe black is gnd, red is - volts and yellow + volts, the 2 pots adjusting each one seperately.
The slide switch inline with the sockets is obviously main power.
The knob on the right looks like it might be a signal generator, and the switch maybe selects one of 2 waveforms, which is then outputted on the sockets.
The 2 pots at the bottom are just wired to their sockets for general use.
Try putting a meter on the left bannana sockets, ground to the black socket, and then probe the red and yellow sockets while twiddling the adjacent knobs, see what happens.
Looking at the date code its early 80's, or someone repaired it with early 80's parts.