Abstract: A small, rugged photomultiplier tube is achieved by closely spacing a large area avalanche "photodetector" with respect to a photocathode in an opaque casing having a window for incident light. The photocathode and the avalanche photodetector have comparable areas and are closely spaced. The avalanche photodetector includes a PN junction which as to be close to the surface of the detector to maximize the response to electrons and reduce any direct response to light. The need for an electrostatic lens to focus electrons onto the small target characteristic of prior art photomultiplier tubes is obviated.