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DER Valves - The Dawn of Broadcasting in the UK
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The John Lawrence Collection
The DER stands for Dull Emitter Receiving. It is a triode with a thoriated tungsten filament, and follows early valve design layout the of a horizontal anode cylinder containing a wire helix grid and a single thin wire filament.
The valve is marked to indicate that the filament voltage is 1.8 to 2.0 Volts at 0.4 Amps. Clearly designed for use with a lead acid accumulator for the filament supply. The anode voltage is to be 30 - 50 Volts.
The valve is marked with the BBC stamp and this places the valve to between 1924 and 1927.
The balloon envelope is 48 mm in diameter and, excluding the B4 base pins is 90 mm tall.
 
Pin Connections
B4
1
2
3
4
a
g1
f
f
 
Absolute Maximum Operating Conditions