Curiosity got the better of me, and I did a quick search to obtain some idea of the extent to which the 6CY5 tetrode was used in American VHF TV practice. I found a couple of examples.
It was used in the Sarkes Tarzian Hot Rod VHF turret tuner of the late 1950s. That the latter had a tetrode RF amplifier is confirmed by Tarzian advertising, and that the tetrode was the 6CY5 was confirmed by a mention in respect of its use in a Hoffman TV receiver:
The 6CY5 was also used by RCA in its KRK71D/E VHF tuner:
Cheers,