A secondary emission multiplier tube

A grid-controlled secondary-emission electron multiplier tube has been designed and built which can deliver an output pulse of five amperes into a load impedance of 100 ohms, with a rise time of less than 10 millimicroseconds and a transit time of less than 20 millimicroseconds. The measured transconductance of the tube is 600,000 µmho, and it can provide a positive output pulse with a positive grid input. This tube is constructed as a series of concentric cylinders, with the grid and cathode structure of a 6AG7 pentode serving as a controlled emitter source. Outside the last grid, a series of four louvered, concentric dynodes are placed, with the first dynode serving as the missing pentode plate. Outside the last dynode are a screen-mesh collector and a fifth dynode. From the fifth dynode, a solid cylinder, the output pulse is taken. The concentric geometry has several advantages. Space-charge difficulties are decreased because the current gain at each dynode may be kept at a high level without increasing the current density in proportion. Furthermore, the geometry is suited to a coaxial input and output for obtaining optimum rise-time characteristics. A tube has been life-tested for 500 hours with a 4 ampere output pulse.