The Type 32 Tetrode Tube

I recently acquired a Ken-Rad Type 32 vacuum tube to be used in a three tube Doerle "Signal Gripper" regenerative receiver that I am building. The Type 32, military designation VT-44, is a product of the 1930's. It is of Tetrode configuration, and was mainly used in radio RF Amplifier circuits of the time.

Tetrode vacuum tubes where invented to reduce the "Miller Effect", or parasitic capacitance between electrodes in a vacuum tube. This capacitance could be detrimental to the efficiency of the vacuum tube at radio frequencies. 

This tube will also be used in an un-tuned RF Amplifier circuit of my "Doerle". The Type 32 was designed for use in battery operated receivers and required only a 2 Volt filament voltage with a 60 ma current drain. Typical radio receivers of the time varied the filament Voltages of the tubes, using a rheostat, to adjust gain and thereby adjust the audio volume coming out of the receiver. You would adjust the filament Voltage lower to compensate for a radio signal overloading your receiver.

A 67.5 Volt screen grid voltage was required to reduce the "Miller Effect" or the parasitic capacitance between tube elements. The Type 32 required a Plate Voltage of at least 135 Volts with a maximum of 180 Volts.  

My Ken-Rad tube has a unique box that allows the inner Type 32 tube to be tested in the box simply by opening the top and bottom flaps and sliding it down until the socket pins are exposed. It could then be easily plugged into a tube tester in order to determine condition. The Type 32 tube would not be powered on long enough to cause the box to get too hot.
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