The Precision Radiation Instruments Model 107, also known as the "Professional," was a Geiger Mueller survey instrument designed for uranium prospecting and/or civil defense.
There is no speaker to provide an audible signal but there is a covered jack on the top of the instrument for headphones. The count rate could also be estimated by observing the small flashing neon light to the left of the meter face. A locked adjustment on the top of the unit permitted the surveyor to adjust the calibration - a source was provided so that the calibration could be performed in the field. It was probably produced between 1955 and 1960.
The differences between the 107, 107B, 107C are not known. From the photos, the 107C has a larger meter, a chrome finish, and the controls are rearranged.
Specifications (107B)
Detector: GM tube (30 mg/cm2), connected to the meter with a
non-detachable cable
Range: 0.2, 2, 20 mR/h.
Batteries: two 1.5 volt, two 45 volt and one 22.5 volt batteries.
Dimensions: 3.5" x 4.5" x 6.5"
Weight: 6 pounds
Price: Model 107B: $139.50 in 1954.
