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The 78 and 78E are variable μ RF pentodes. This exhibit has no manufacturers name, just that it was made for the US Navy.

The RCA Receiving Tube manual describes the 78 as being electrically identical to the IO based 6K7 apart from the capacitances, thus this is one of the Magic Three valves.

Thanks to Peter for identifying the CKR on the base as the abbreviation for Ken-Rad.

The sheet screen obscures the electrodes.

The classic envelope is 38 mm in diameter, and excluding the UX6 base pins is 96 mm tall.

References: Data-sheet, ¹⁰⁴⁰, ⁴⁰⁵⁵ & ¹⁰⁴³. Type 78 was first introduced in 1937. See also 1937 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.