Recently I was fortunate enough to acquire a Ludlum Model 16 meter for my collection of equipment. After opening the package I was pleasantly surprised, it is used, in fairly good shape, and much smaller than I expected. It was about the size of a Universal Atomics CDV-700 geiger counter. According to the manual I located online (http://www.drct.com/dss/INSTRUMENTATION/Ludlum/Ludlum_Manuals/Ludlum_Model_16_Analyzer_Manual.pdf), it was made before 1992.
I did have some problems when I first hooked it up to the probe, the BNC connector was not connected correctly. No amount of voltage supplied could get one click out of the Ludlum, and I had no reason to believe that the probe was DOA. Months earlier, I had connected the Male adapter to the probe, and may have done it wrong or broken some of the fine wires.
After reattaching a new BNC connector, the results where much, much better. Clicks where immediately heard coming from the speaker, however, it was not much better than a Geiger Tube, and it appeared to be not much more sensitive to the gamma rays emitted from the radium found in a 1B29 transmit tube (a military spark gap vacuum tube for a 1940's era radar unit). After an hour of adjusting the voltage sent to the scintillator probe, and adjusting the gain of probe, I finally was able to to get satisfactory results.
Hopefully with this unit in my car, I will be able to find more sources of radiation around town...