I bought a few and trying to test one. The voltage divider is DIY soldered on the B12A connector.
The voltage divider schematic is basically the same as the Bicron P-12 with a few changes: base resistance is 1.2 Mohm, R1 = 3R, R7
= 1.5R. According to a research paper available online, the detector uses a Hamamatsu R3998, so the resistances are changed to
get the voltage distribution ratio as per the datasheet.
- Bicron B-12 PMT Base schematic
test source. Most detectors work fine with bias around 500-700V and 10x-20x gain. For the 35BR51 I start getting spectra at about 1000V bias and 300x gain.
I double checked the divider assembly, checked the voltage between the dynodes, tried another 35BR51 with the same unsatisfactory result.
What the hell is with these detectors?
Non-standard B12A pinout?
Any ideas?
