The 6B8 American metal valve is a double diode pentode. Such valves were made for the signal detector, AGC detector and first audio amplifier stages of superhet receivers usually as a double diode triode. This valve with a vari-μ pentode offered the set designer the option of using this as final IF stage plus detectors. For local reception a pentagrid converter (heptode), this valve and sensitive output valve may have been all that was required apart from a rectifier.
This valve is also marked with the American procurement specification of VT-93.
The 12C8 is electrically identical but has a 12 Volt heater.
The Ken-Rad name and the code SC961A that appears on other exhibits.
Made in USA.
The top cap - an extra complication in making a steel envelope.
The original box and the line 'accepted June 1944 SC961A' indicates that SC961A is the identification of the test site.
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 6B8 was first introduced in 1937. See also1937 adverts.