The Type 57 is a pentode designed for use as a biased detector. It features the original American specification for indirectly heated valves - a 2.5 Volt heater.
The 6J7 was a later implementation of the design and RCA say the characteristic curves are the same for both.
This exhibit was clearly made for a UK Government contract as the base carries the Air Ministry Crown and letters A and M together with the old stores code of 110E/132.
looking up from the base the cylindrical anode on the outside with the three wire grids within. The lower screening disc is connected to the round cathode tube.
The top screen with the control grid connected to the top cap.
The classic envelope is 38 mm in diameter, and excluding the base pins is 105 mm tall.
Reference: Data-sheet. Type 57 was first introduced in 1932. See also1932 adverts.
