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.Unlike our other examples this example has a rounded balloon envelope rather than the shaped form.
The reverse is plain zinc loaded screening paint.The classic envelope is 35 mm in diameter and excluding, the B5 base pins, is 77 mm tall.References: Data-sheet & 1043. Type 2D4A was first introduced in 1934. See also 1934 adverts. |
