Hi!
I've just been dissecting an old German Wetzel tube mic. Here's my sketch of the schematic.
A couple of unusual features here.
One is the use of light bulbs as part of the heater supply filter network.
Another is that the capsule is referenced to the cathode of the first tube stage, rather than to ground. I don''t recall seeing that before.
One thing that's puzzling me is that the PSU gives exactly 6.3V when run off exactly 220V (variac), but the tube (ECC83) seems to be wired for 12V operation (pins 4 & 5). It doesn't look like the mic has been modified at all (before I got my hands on it). Could be a factory error, or that the PSU is really for another model, although both mic and PSU have the same manufacturer's name and the components look to be a similar vintage.
I'll get some photos later.
I've just been dissecting an old German Wetzel tube mic. Here's my sketch of the schematic.
A couple of unusual features here.
One is the use of light bulbs as part of the heater supply filter network.
Another is that the capsule is referenced to the cathode of the first tube stage, rather than to ground. I don''t recall seeing that before.
One thing that's puzzling me is that the PSU gives exactly 6.3V when run off exactly 220V (variac), but the tube (ECC83) seems to be wired for 12V operation (pins 4 & 5). It doesn't look like the mic has been modified at all (before I got my hands on it). Could be a factory error, or that the PSU is really for another model, although both mic and PSU have the same manufacturer's name and the components look to be a similar vintage.
I'll get some photos later.