The 7A4 is a medium-mu general purpose triode that is electrically equivalent to the IO based 6J5GT. The use of the all glass construction (elimination of the pinch and long internal connections etc.) allows the 7A4 to operate at higher frequencies than the 6J5.
The Type designation is carried on the dome. Here the lettering is badly degraded.
The Loctal base features a spigot that engages with a spring in the base to hold the valve securely in place.
Thanks to Mark Mallison for sending the images.
The wide glass tube envelope is mm in diameter and, excluding the footless base pins, is mm tall.
Reference: Data-sheet & Data. Type 7A4 was first introduced in 1940. See also1940 adverts.
