The EL37 audio output valve is of pentode configuration and is Mullard’s answer to the mighty KT66 beam tetrode. These meaty beasts could deliver up to 70 Watts at 2.5% distortion when used in push-pull.
Developed from the earlier EL31 and rerated to have higher anode dissipation, the EL37 in characterised by having a massive mutual conductance when compared against it’s contemporaries. Indeed, 11.0 mA/V is almost twice the value of that shown by the KT66 or the 6L6.
Introduced in 1946, the EL37 was superseded by the introduction of the EL34 some 8 years later, praised for their scarcity, their exceptional sound and ease of driving they are keenly sought for audio amplifier and guitar amplifier applications today, key examples of which include: -