Pin 1 is connected to the screen grid (g2) as a second screen connection, unlike the 6L6 where pin 1 is the metal shell or NC. This prevents direct pin-for-pin substitution with the 6L6 family without verifying pin 1 wiring in the circuit.
The Mullard datasheet specifies Rg1_max of 0.5 MΩ for cathode bias and 0.1 MΩ for fixed bias.
Triode-connected limiting values differ depending on application: normal use allows Va+g2 max of 400 V and Wa+g2 max of 28 W, while cathode-coupled push-pull driver stages allow Va+g2 max of 500 V and Wa+g2 max of 12.5 W.
The EL37 was introduced in the mid-1940s and was Mullard's answer to the KT66 beam tetrode. It was notable for requiring very little drive signal to reach full output, making it popular in high-fidelity amplifiers of the late 1940s and 1950s.
Pin Layout — Octal
1Screen Grid (second connection)
2Heater
3Anode
4
Socket-Compatible Tubes ⚠ Not electrically compatible