The 14S7 is a post war triode heptode frequency changer. The American valves with designations starting with 14 were designed for operation on nominal 12 Volt vehicle supplies. Brimar do not give the operating frequency in their short form catalogue. The 7S7 has identical operating characteristics but with a standard 6.3 Volt heater.
Here, through the internal coating, can be seen the oscillator triode mounted above the heptode mixer on the common cathode.
The remains of the Brimar name and Made in England that were printed onto the glass in orange paint. The Loctal spigot and locating pip are clear to see.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 56 mm tall.
References: Data-sheet & 1040. Type 14S7 was first introduced in 1948. See also1948 adverts.
