The 6F6G output pentode was designed for audio amplification in radio receivers. The operating values given are for single ended use with an anode load of 7,000 Ω.
If a pair are used as an audio amplifier in push pull class A, 10.5 Watts are possible with 3% distortion.
The equivalent type KT63 is a beam tetrode. Type 42E is electrically the same but with a UX6 base. Additionally the 7D5 is a 6F6G with a 0.315 Amp 13 Volt heater and a B7 Base cap.
The Westinghouse name and made in Canada on the base cap. Through the internal coating can be seen the three grid supports. The valve electrodes are spot welded to the shaped supports that originate within the pinch.
The top of the valve. The control grid copper supports are topped off with a U shaped heat radiator.
The classic envelope is 44 mm in diameter and excluding the IO base pins the length is 96 mm.
References: Data-sheet, 1040 & 1043. Type 6F6G was first introduced in 1937.