The 6L7 was designed to ensure maximum isolation between oscillator and signal, and to provide a mixer which is efficient at VHF. At VHF 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 and is fed to g3. The signal feed to the top cap is typical of the period and this arrangement is to improve signal isolation.
The Philco brand and country of origin.
The request to the user to keep using Philco products.
The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 62 mm tall.
References: Data-sheet, 1040 & 1043. Type 6L7 was first introduced in 1936. See also1936 adverts.