High Power Tetrode

Ref. F9

This huge Eimac 8189 4PR1000A tetrode tube was removed from the high tension circuit of a CT scanner. This tube dates back to the late 20th century but its conception and earlier makes were already described in catalogs dating from the late sixties.

Tetrodes of this type and power had many uses, mainly in transmitters. It could be used as oscillator, pulse modulator, or power amplifier. Its role in the high tension circuit of the CT scanner is not defined.

In its technical specifications we note the plate (anode) voltage can be as high as 30kV, and for short cycles the filament current 8Amps. During use the tube becomes extremely hot, and the ribbed plate red hot. Cooling during operation is therefore a must, and is achieved by forced air coming from the bottom and running upwards around the tube through a specially provided Pyrex glass chimney. (Eimac Model No. SK506).

Tetrodes of different sizes and different powers are used in all control units of different high power X-ray equipment, mainly in the circuits of the exposure control.