The 6J6 is definitely 'all-American' and the ECC91 is a later copy. We fear much the same is true of many familiar 'British' valve types! - copies of American designs.

The B7G all-glass form of 'button base' construction is also of American origin, dating from the early 1940s. Type 6J6 was one of the earliest B7G valves and probably could not have been made successfully using a conventional 'pinch' structure. Early specimens have a quite distinctive 'waist' where the button base joins the tubular glass envelope. This, and the US Navy WW2 'anchor' logo show that our exhibit is one of the early ones.

Once teething troubles had been overcome and B7G mass-production machinery was in place in support of the War Effort, B7G types could be made more cheaply than conventional Octals and Loctals so, particularly after the War as military demand diminished and consumer demand rose, this machinery was put to good use making miniature versions of 'ordinary' consumer valve types irrespective of whether the pinchless button construction conferred any technical advantage. One snag was the availability of only 7 pins so some ingenuity was required when miniaturising conventional 8-pin valves. This soon lead to the development of the B9A button base which has remained the world standard ever since.

This miniature double triode was used for VHF signal amplification.

The construction has a common flattened tube cathode, with the control grids either side. The anodes are U channel sections either side of the central cathode.

The thin glass tube envelope is 18 mm diameter and 44 mm high excluding the B7G base pins.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	a(2)	a(1)	h	h	g(1)	g(2)	k

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	6.3	0.45	100	-0.85	8.5	7100	5.3

Thanks to Frank Philipse for supplying the above datasheet

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This exhibit was last updated on 04 July 2007 {find valves by name}