We believe RCA's metal 6L6 was the World's first true aligned-grid beam tetrode to reach Quantity Production status (around 1935).

A successful pre-production batch of the British (M-OV) type KT40 was produced at least a year earlier but its routine production was delayed and eventually abandoned because 'it was too difficult to assemble'.

Once RCA had showed that it could be done after all, M-OV copied the 6L6 with modifications thus producing the famous KT66.

The 6V6 receiver type of beam tetrode with which it shares pin connections is a derivative. This valve was mainly used for audio amplifiers.

The 807 was based on the RCA type 6L6 beam tetrode, which had a long, fairly thin, anode and a carefully-aligned grid structure. The 6L6 employed rapidly-accelerated electrons and short electron paths. This made it efficient but its characteristic had a distinct residual kink. It was a very successful valve but its characteristic was not quite straight enough to give the ultimate in audio quality at high output levels.

The KT66 was essentially a 6L6 redesigned with a larger cathode and a shorter, fatter anode. The KT66 had less rapid acceleration, longer electron paths, and almost no kink. It was ace for audio hi-fi.

A pair of 6L6's working in class AB2 push pull would deliver 47 Watts at 2% distortion. A lot of power in the 1940s and 1950s.

The metal tube hides the inner construction. Our all glass 6l6GT version has a description of the electrode construction.

The wide metal tube envelope is 30 mm in diameter and excluding the IO base pins, is 90 mm tall.

References: Datasheet and private correspondence. Type 6L6 was first introduced^¶ in 1936.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	g2	g1	nc	h	k

 
Absolute Maximum Operating Conditions^¶

Beam Tetrode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout	D
	6.3	0.9	350	250	-18	54	2.5	33K	5.2	11W	15%

Thanks to Frank Philipse for supplying the above PDF datasheet

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