As well as microphones, Grampian made amplifiers and other PA equipment. Here's an old Grampian amplifier and speaker set.
I found the amp a few years ago in Dave Dee's junk shop in York. The circuit is actually very similar to a Mullard Twenty, with the addition of a transformer balanced mic input, and several taps on the output transformer for 8 ohm loudspeaker or 100V connection. I have even used this in the past as a mic preamp for recording, for some warm and slightly dirty vocal tracks.
The speaker is a recent purchase found on GroupDIY.com. It has a rather nice and unusual tapered shape, with (no longer very) white vinyl covering. The whole set has a really cool vintage look to it - very different from today's ubiquitous square black boxes.
I am now using this as a guitar rig - it has a great vintage valve tone with just the right amount of breakup coming from the speakers. There is plenty of volume for recording, but I would hesitate to use it for rehearsals with a modern loud drum kit!
I am unsure of the age of these but I would guess 1950s or early 60s - they don't appear in Grampian's 1968 product line, and presumably pre-date that. If anybody knows more, please get in touch.