The DH719 is a triple diode triode. The triode and two diodes share a common cathode but one diode has a separate cathode.
The DH719 (EBC80) was specifically designed for use in the detector stage of early FM and FM/AM radios. The triode section providing the first audio amplification, the single diode and one of the diode pair were used as an FM detector in a ratio detector circuit. SeeFM Broadcasting and Signal Detection. The other diode in the pair being used as the AM detector when that part of the circuit was required.
The triode anode and the diode outer screens are all the same size. The bars on the left connect the base pins 4 & 5 to the heaters above the top mica.
The reverse is cleaner and the detail of the sections can be seen. The diode anodes are simple vertical rods.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 58 mm tall.
References: Data-sheet & 1040. Type DH719 was first introduced in 1955. See also1955 adverts.
