The 7K7 is a double diode triode typical of the late 1940s in the UK. The diodes would be employed as signal detector and ACG rectifier whilst the triode would be the first audio voltage amplifier. Unlike earlier designs such as the 6Q7 the control grid is not taken to the top cap. The shorter internal pathways making it easier to avoid instability.
The Brimar identification and Made in England.
The triode is on the left. On the right is the double diode with screen connected to the cathode at the top.
The triode is orientated at right angles to the diode anodes seen on the right. The diode anodes are just two plain rods placed either side of the central cathode.
The diode screen identical to the triode anode and diode anodes may be made of the same wire as the grid supports.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 57 mm tall.
References: Data-sheet & 1040. Type 7K7 was first introduced in 1938. See also1938 adverts.
