I recently acquired an LND-712 Geiger tube. The schematic that LND provided shows how to wire to the detector, but I don't know what "signal" is supposed to represent. Here's the schematic: http://www.lndinc.com/products/711/. Can anyone help?
"Signal" will be the signal you process to make the clicks & stuff normally associated with a geiger counter.
So signal will be running to the detector, not the ground of the tube?
The signal is a very short needle-like shaped pulse (~10-100usecs, it depends on the input impedance of the next stage) with random frequency, between 10 pulses per minute to 5000 pulses per minute with normally available rad. source, and with few volts amplitude (5-50V maybe more).
You need a high impedance coupling (ie jfet) to process the pulse properly.. The 50pF capacitor must be at least 2kV rated to be safe.
There are several possible wirings of a GM tube, just google it.
Mind the high voltage is lethal!