It also occurred to me that the Mazda 30F27 would have been suitable for use as an RF amplifier in FM tuners and receivers. Whether Mazda ever promoted this end-use I don’t know.
At the time, triodes, pentodes and cascodes were used as FM RF amplifiers. The triode was probably dominant, mostly as half of an ECC85 or similar in a single-valve front-end, but not universal. Although pentodes were noisier than triodes, evidently the typical in situ difference at Band II frequencies was not enough to preclude the pentode from use in higher performance units. The 30F27 would have offered pentode performance and simplicity, with a lower noise level that was probably not too far above that of a triode.
A 1961 Tarzian advertisement shows that by then, it was also offering an FM front end as well as two types of TV tuner:
Possibly the FM tuner also used the 6CY5 as RF amplifier, the same as the Hot Rod TV tuner. Whilst a proprietary FM front end was not in and of itself unusual, a two-valve type – as a separate unit - might have been. On the other hand, the single-valve type, originally developed I think in Germany, was legion amongst the third-party makers. It reached the USA in the later 1950s via imported radio receivers from the likes of Telefunken and Grundig, and by 1959-60 had been taken up by General Instrument and Standard Coil, both major TV tuner makers.
Looking at UK practice, the single-valve FM front end, from both in-house and third-party sources, was widely used. Where more elaborate FM front ends were required, these seem to have been designed and built as an integral part of the chassis rather than as bolt-on units. The only exception that I have noticed (from web pictures) are the Dynatron T10A and T11 models, which appear to have a “bolt-on” two-valve unit, the original T10 having used a single-valve unit.
The 6CY5 and 30F27 were not alone; there were other small-signal RF tetrodes of that era.
Sylvania offered the 6C9 dual tetrode (on a decar base) for use in FM front ends, one tetrode as an RF amplifier and the other as a self-oscillating mixer. I’d say it was intended to provide a tetrode option for single-valve front ends.
But the “triode lobby”, as it were, was not standing still. The 6EZ8 was a triple triode, intended for use as a combined FM RF amplifier, self-oscillating mixer and AFC valve. Or it could be used as an RF amplifier and mixer with separate oscillator, or as a mixer, separate oscillator and AFC valve. And the 6JK8 had one frame-grid triode, for use as an FM RF amplifier, and one conventional triode, for use as a self-oscillating mixer.
There were a couple of triode tetrode VHF oscillator-mixers intended for V use, namely the 6CL8 and 6CQ8. And another couple of VHF amplifier tetrodes, the 6EV5 and 6FV5. So, it does seem as if the VHF tetrode garnered some attention in the American market.
Cheers,