This Brimar 6L7 in the metal can was made in the US. It is probable that all these metal valves were imports to the UK.
The whole point of the 6L7 is to ensure maximum isolation between oscillator and signal, and to provide a mixer which is efficient at VHF where stable oscillation would require a separate VHF oscillator triode.
For applications where a self-oscillating mixer (i.e. pentagrid converter) could provide adequate performance there were other Octal types specifically designed for this purpose.
The oscillator injection needed to be 18 Volts peak to peak. The signal feed to the top cap is typical of the period to improve signal isolation.
The reverse of the can is plain.
The complex structure required for a top-cap connection in these metal valves.
The original Brimar box measures 36 mm square and is 94 mm tall.
The centre section pushes out from the sleeve and within is a corrugated card liner.
The corrugated card is folded to enclose the small diameter of the metal envelope.
The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 63 mm tall.
References: Data-sheet, 1040 & 1043. Type 6L7 was first introduced in 1936. See also1936 adverts.
