Summary

General purpose triode. This type was released in 1922 as a dull-emitting version of the R valve, hence the DER designation. It continued in production with various bulb styles for about ten years. The triangular label on this example indicates that it was made in or after 1930. Used as a Class A audio amplifier.
Manufacturer: MO Valve Company, England.
1.8 V directly heated cathode.

Physical Description

Conical bulb with 4 pin European style base.

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