The 7B7 is a high impedance variable μ amplifier pentode. It was probably designed for IF amplifier use, with a tuned anode circuit.

It is interesting to ask who made the valve. We believe that it is not Cossor as labelled. Construction details are typically American and we have seen Cossor-labelled valves of this vintage (c. 1950) clearly marked 'British Made' (as here) and (on the other side) 'made in USA'. Similar-looking valves were also factored under several other 'big-name' labels around this time.

The wide glass tube envelope is 27 mm in diameter and, excluding the B8B base pins, is 55 mm tall.

 
Pin Connections

B8B	1	2	3	4	5	6	7	8
	h	a	g2	g3	s	g1	k	h

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.15	250	100	-3	8.5	1.7	0.75M	1.75

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 05 July 2007 {find valves by name}