Hi Gus, thanks for chiming in!!
My tech definitely knows (very good tech!), but I'm out of funds for this, so I'm on my own for now....
I, as you will have noticed from my questions do not know to much, but am careful to definitely not touch anything powered up other than the chassis with one hand or something I've had the meter on first. I'm guessing the tube and the little electrolytic are the main contenders for shockage??
The tubes are most probably good, but I have tried it with an EF86 (as I can crank the voltage to 6.3V with the pot) which is definitely good, same result.
I do not have a signal generator or a scope unfortunately....will check the backplate to mount with DMM.
Wires are the ones that Dale's M7 arrived with, bar the one soldered to the outside of the mount of course(backplate).
I have repeatedly cleaned the whole board, including the capsule to tube area with 100% isopropyl....no difference, and yes there is literally nothing in the diy microphone meta's which I haven't read at least once (the 'on-topic' stuff more like 2-4 times....)
One thing I just noticed this morning when trying again is that now (since I refitted the capsulemount with electrical tape around the screwstem for isolation) I have a random crackling in there, aswell as the same miniscule signal. Also, the cable (original chinese 7-pin) seems to be somewhat unhappy, as it creates interference when moving it. This happens even when the PSU is not connected.......??
As I can't do most of what you suggested without a signal generator, I'm off to put the DMM on the mount/backplate......will report back.
Thanks again!