ML6 is the 6.3 V vehicle-battery version of the ML4 (4 V mains-heater version). Same envelope, same B5 5-pin base, same triode structure and electrical characteristics; only the heater rating differs.
British military / RAF designations: CV1105 (joint-services CV number), VR105 (Air Ministry 'Valve Receiving' designation), VT105 (RAF Type code). The ceramic-base wartime variant is sometimes marked ML6C.
Used during WWII as an RF oscillator in medium-sized military transmitters (per The Valve Museum / r-type.org).
Anode dissipation rating: the ML4 datasheet states the valve can be allowed to dissipate the equivalent of 5 W in transmitter / oscillator service; this same rating applies to the ML6.
Pin functions on the B5 base: 1 = Anode, 2 = Grid, 3 = Heater, 4 = Heater, 5 = Cathode (per the Osram ML4 datasheet, which the ML6 inherits).
Triode physics check: gm × ra / 1000 = 3.8 × 3700 / 1000 = 14.06 ≈ mu (the Valve Museum lists no separate mu value; the implied amplification factor is approximately 14, consistent with the ML4 family).
Capacitances are taken from the ML4 datasheet (the ML6 datasheet was not located separately): Cga ≈ 6.3 pF, Ca-others ≈ 4.5 pF, Cg-others ≈ 7.2 pF.
Brans Vade Mecum lists ML6 in table IIIa (small-signal triodes) with equivalents CV1105, D105.