20 Nov
2008
20 Nov
'08
10:14 a.m.
Matthew Smith wrote:
Quoth Folderol at 2008-11-15 21:49...
I doubt it'll be a selenium cell LDR, that wouldn't really be fast
enough for 3kHz. What you might find is that it's an early photodiode,
consisting of a thin metal rod for the anode and a C-shaped cathode.
There are special coatings on them, and the current flowing through
changes with the amount of light falling on the cathode. They need
biased to about 150V to work properly, but you should see *some* sort of
output with as little as 9V.
Gordon
Fascinating bit of kit. I'd be inclined to
try to keep it as complete
and original as possible. I doubt you'd have a problem with the
capacitor. I know someone with a WW2 communications set that still has
almost all it's 'dry' caps, and only half the electrolytics have been
changed.
I have to confess, I do feel an urge to restore it.
I will certainly do preliminary tests (once I've got the thing spinning)
with and LED and a phototransistor, just to see what it sounds like, but
getting a proper setup with the lamp and selenium cell seems like the
Right Thing To Do.