One of my Facebook Groups (UK Vintage Radio Repair and Restoration) had an enquiry recently from a lady who came across this equipment when clearing up her deceased father's effects. Photos are at:
The chap was "an avid military collector, mainly vehicles" so presumably the kit was part of a mobile PA system. It seems (from the scant info on line) that this was the first in a series of amps that ended up in the twenties.
I've suggested that she contacts the Signals museum at Blandford, but if anyone here can shed any further light, I'll relay the information.
Best regards ............... Bill Atkins
(Font size increased by moderator)