So, it may be a Molex connector, like in a PC, or something similar which is rated at a higher voltage.
and the pins are:
Ground (power and signal)
+ve rail, which may be 30V, 36V, or perhaps 71V, current unsure.
Signal.
-ve rail, as per +ve.
n/a
n/a
I'm pretty sure it's originally from a head or combo, but the power supply/amp stage has presumably shuffled off this mortal coil and so the question is whether it can be converted to a standalone preamp and whether it is worth the effort.
The background is I've been looking at buying it, probably for £50, but I think I'm going to pass, as it'll just be another project for me (I seem to collect projects!).
If anybody's interested, it's on FB Marketplace: https://www.facebook.com/marketplace/item/564451868674188/