Mullard designate the EF37A as a high gain, high impedance, pentode for use in AF pre-amplifier stages. The electrode system is of anti-microphonic construction, and the specially designed bifilar wound heater reduces hum to negligible proportions.High quality amplifiers have used the EF37A for many decades. The ME1400 electrometer pentode is also rated for high quality audio use and is a direct replacement for the EF37A upon which it was based. The EF86 was its successor.The data sheets also give parameters for use as a triode.See also 6J7 almost the same valve in operation.This exhibit is useful as some of the external metallising paint has broken away to reveal the inside.
The bright anode with grids extending beyond.
Here the three grids can be seen as well as the white cathode. The outer suppressor grid windings are far from the centre and a very open pitch.
A closer view - taken with the microscope.
The three grids. The notch and peen fixing of the screen grid wire to the support is particularly clear.The classic envelope is 30 mm in diameter and, excluding the IO base pins, is 86 mm tall.References: Data-sheet, 1004 & 1040 Type EF37A was first introduced in 1942. See also 1942 adverts. |
