I recently bought a Ludlum Measurements model 2A survey meter on eBay from Obtanium. This is a nice meter which features the well known rugged Ludlum design, adjustable HV and 3 ranges of 500, 5000 and 50000 counts per minute.
Using a scintillation probe the meter easily saturates on the 500 cpm scale, and the 5k and 50k ranges are also overloaded with certain sources.
So I thought of adding a 500k cpm range. I already read the manuals and associated schematics to find out how to do this.
Ludlum model 2 and 3 offer about the same functionality and basically share the same PCB, circuit, knobs and switches. Depending on age and model there are certain differences, but a lot of the stuff and functionality is the same. Continue reading