Type 6F6 is a general-purpose audio output pentode intended for domestic and car radios. Its output is similar to that of the 6V6 but it was more sensitive with the ability to be driven directly from the detector output, thus saving one stage of audio amplification - a boon for car radio design.
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 6F6 was first introduced in 1936.