See it now. It looks like an unregulated supply. I can see bridge rectifier and some caps only at the main PSU section.
It will probably be bipolar, since there are appear to be a couple of caps in a couple of places.
In a couple of photos there is what looks like a simple regulator board at the end, feeding a single PSU rail along one strip of modules (red and black wiring). It has a trimmer on it, probably to adjust the rail voltage. It appears to be responsible for another regulated rail. The wiring to the input modules appears to come from somewhere else.
However the channel circuitry appears to use those old (and noisy) tin-can 741 op-amps. These usually need a bipolar supply of around +/-12 to +/-15V. Since it appears unregulated, it is likely to be +/-12V, since line surges could destroy the op amps if they are run too close to their maximum ratings. Tracing out the wiring to the power pins of the op amps would identify what the power source is for these.