General Electric 1P24 Photocell Tube (VT-280)  
Written by AnubisTTP on 2017-07-08  



The 1P24, manufactured by General Electric, is a small cartridge type phototube designed for use in World War 2 era T-4 rocket fuses. This device takes the word 'vacuum tube' to a literal level... the interior of the tube is little more than empty space. One end of the device contains the anode, while the other end contains both the photocathode and evacuation nipple. The photocathode has a small hole in the center, which allows air to escape the tube during the pump-down process. The interior of this tube is a complete vacuum, unlike many other photocells which are filled with an inert gas such as argon. When installed in a photoelectric rocket fuse, the 1P24 would be surrounded with an annular lens that would provide a 5 degree field of view in a ring around the entire circumference of the rocket. As the rocket passes alongside an enemy aircraft, the craft's shadow would fall on the annular lens, triggering the rocket to detonate.

RMA 1P24 Phototube Datasheet (PDF, 55kb)


General Electric 1P24 Tube
General Electric 1P24 tube.

T4 Photoelectric Fuse
The 1P24 phototube was designed for use in WW2-era photoelectric antiaircraft rockets. Shown here is a cutaway diagram of a T-4 photoelectric fuse. The 1P24 photocell can be seen in the nose of the device.

T4 Photoelectric Fuse
This US Army photo shows a 1P24 prototype (upper left) alongside various attempts to reduce the size and weight of the tube, none of which appear to have entered production. The bottom left tube includes a built-in thyratron, which is contained in a separate cylindrical envelope fused to the top of the photocell tube.

T4 Photoelectric Fuse
Electrical power was a significant problem for WW2-era electric rocket fuses. The standard T-4 fuse was powered by a battery which prevented the rocket from being stored in a ready to use state; the battery would have to be installed shortly before the rocket was used. Shown above is a T-4 fuse that has been modified to be powered by an internal generator. Air pressure from the rocket's forward travel would spin a turbine, shown at the top of the image, to power the fuse while in flight.

1P24 Photocell Tube Pinouts
1P24 phototube, pinouts and dimensions.

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