Manufactured by STC (an ITT associate company) in the UK. Designed for wide band repeater amplifier service in coaxial carrier telephone systems.
Also found use in high-quality audio applications, particularly as a cathode follower stage for matching condenser microphones to low-impedance mixing desk inputs.
Uses Loctal (B8G) 8-pin base. Pins 2 and 6 are internal connections; pin 3 is no connection.
Typical operating point: Va = 150 V, Vg = -1.5 V, Ia = 40 mA. At this point gm = 47 mA/V, ra = 1000 ohms.
The STC datasheet states this tube is identical with the American type 437A.