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The CV3990 (commercially the 2E26) is a small VHF transmitting beam tetrode that was typically used in mobile transmitters. As a single ended Class C RF amplifier it would generate up to 5.5 Watts in the VHF range to 125 MHz.

If used in push-pull with up to 500 Volts on the anodes the pair could produce up to 50 Watts but 27 Watts would be more typical. The maximum dissipations of 10 Watts anode and 2.5 Watts for the screen had to be observed and so it is probably that they would have been used for telephony rather than CW.

As with other transmitting valves the design allowed them to be used as AF modulators as well. For AM modulation the CV3990 would be used as either class AB1 push-pull or single ended for low powers. With this dual use the transmitter would need fewer valve types as spares. This was particularly required in mobile communications.

The KB/D identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the D identifies the maker as Mullard Radio Valve Co., Mitcham.

The box anode and top screening.

The folded anode is sealed together with this flange.

Maker's codes.

The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 75 mm tall.

References: Data-sheet & ⁴⁰³⁸. Type CV3990 was first introduced in 1962. See also 1962 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.