Sensibly equivalent¶ to:
The Marconi-Osram Valve company produced the first dull emitter valves in 1921. The gold-pink envelope is characteristic of phosphorus gettering.
Markings on the envelope indicate that it was a dull emitter R-type, and that it was produced as part of the BBC consortium.
The internal construction clearly follows the pattern of the early R-type valves. The amplification factor was 9 for the DER, the same as for the R-type.
The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 98 mm tall.
Reference: 1003. Type DER was first introduced in 1921. See also 1921 adverts.
Absolute Maximum Operating Conditions¶
Updated November 16, 2016.