The EF37A is the 'A' revision of the EF37, with improved low-noise performance and more consistent manufacturing. Both are octal (IO/B8G) based.
Widely used in BBC and professional audio equipment in the 1940s and 1950s before being superseded by the EF86.
Pin 1 is the metallic screen/shield connection — must be grounded for lowest noise and hum.
Suppressor grid (g3) is brought out to a separate pin, allowing external connection. For pentode operation, connect to cathode.
Triode strapping is achieved by connecting g2 and g3 to anode. No triode-strapped data is available in the Schlangen reference for this type.
Datasheet not available from frank.pocnet.net; specifications from Mullard published data and cross-referenced with Brans Vademecum and Philips interchange tables.