That brings back memories. We had one in the shop. Finally had to stop using it once we couldn't get the 22.5V batteries that it ran on any more.
I seem to recall ours had a TRS (B-gauge) jack for the input rather than binding posts, but maybe that was on the side. There was a wooden cover for it as well, which when closed turned off the power switch. But if you just left it sitting there with the power on, the battery would be drained after a day or so.
I put a [used] WBS XTM4 extended range VU/PPM meter in a studio recently. That's a beautiful piece of kit.
Geoff Doane,
Halifax, NS