Sensibly equivalent¶ to:
The A20B from Ever Ready is a Mullard 2D4A supplied under licence. As the base matches the Mullard device and it is suspected that that was made by Philips in Eindhoven, then it is probable that this also had a Dutch origin.
Electrically the valve is 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 classic envelope is 28 mm in diameter and excluding, the B5 base pins, is 72 mm tall.
References: Datasheet & 1043. Type A20B 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