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.
The reverse has had the metal screening paint removed and the inner structure is made plain. The heater is bifilar wound on an insulating mandrel. The cathode tube is closed at the top and this reduced diameter tube is then held within the top mica. The anodes are made of sheet nickel, folded and with a cylindrical end through which the cathode tube passes. The anodes are stacked vertically.
The classic envelope is 28 mm in diameter and excluding, the B5 base pins, is 72 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 July 06, 2017.