I’m currently building a GM counter for a friend and was looking for nice, low
power circuits working on 9V cells.
I found this circuit which is derivative of Charles Wenzel’s designs:
http://www.mikrocontroller.net/attachment/103170/Geiger_Hochspannung.png
Components are fairly basic apart from the HV transistor and zeners. The other
transistors can be basically any small signal PNP/NPN transistor from the
junkbox. I used BC547 and BC557 and a MPSA44 HV transistor. Continue reading Post ID 1068