The TDD4 is an indirectly heated double diode triode for mains superhet receivers. It was designed for signal and AGC detection and then as the first post detection amplifier.
We have several versions, this is believed to be of post WWII manufacture but the design dates to 1933. The style of the Mullard logo is the guide.
The reverse is plain zinc loaded paint in the Mullard gold colour.
The dome reveals little of the internal construction other than that the triode is at the top.
The classic envelope is 40 mm in diameter and, excluding the B7 base pins, is 101 mm tall.
References: Data-sheet & 1043. Type TDD4 was first introduced in 1933. See also1933 adverts.
