Sensibly equivalent¶ to:
The 2D4A valve houses a pair of signal diodes with a common cathode. The valve design is from 1934 and the diodes would have been used for demodulation at, probably at around 455 - 500 kHz, the IF frequency of broadcast radio receivers.
The 2D4B has the same electrical characteristics but is on a B7 base and has the greater versatility of separate cathodes.
This specimen is interesting because certain details of the base cap make us suspect that this valve was made at the Philips factory in Eindhoven (Holland) and imported. Probably only the 'Mullard' marking is 'British Made'. This would apparently contradict the terms of the BVA Cartel agreement which enabled Philips to exploit the British domestic market via the Mullard subsidiary.
The classic envelope is 30 mm in diameter and excluding, the B5 base pins, is 75 mm tall.
References: Datasheet & 1043. Type 2D4A was first introduced in 1934.
Absolute Maximum Operating Conditions¶
PDF scanned from an original document held by the museum
Updated December29, 2012. shape:classic construction:pinch type:double.diode age:1930.1940 base:b5 heater:4.0v pins:5 pin:1.a(1) pin:2.a(2) pin:3.h pin:4.h pin:5.k