The 6CS6/EH90 had an odd history, see:
https://www.vintage-radio.net/forum/...6&postcount=15.
By the time Philips picked it up for use as an FM demodulator, the US industry was using later dual-control pentodes sych as the 6GX6 for FM demodulators of the dual-mode locked oscillator/passive quadrature type. Also, for the noise-gated sync separation function, the 6GY6 dual-control pentode and 6BU8 (& successors) double dual-control pentodes were used.
Just as the US industry initially used the radio frequency changer 6BE6 as a noise-gated sync separator, Philips used the ECH81 for the same purpose, then moving on to the ECH83, billed as both a 12-volt-HT car radio valve and a TV valve. That in turn was replaced by the ECH84 (noval base) at approximately the same time that the EH90 was introduced for the FM demodulation job. Later came the ECH200 on the decal base.
Amperex did offer quite a few of the Philips valves for TV use in the USA, and they were used by some major setmakers such as Zenith. Noval-based VHF pentodes were novel
[groan] in the USA, where B7G was the norm for this type, but apparently the EF183 and EF184, under their respective American numbers, were regarded as offering desirable performance characteristics. I think that Amperex did offer the ECH200 in the USA, but I don't know about the EH90 - need to check that
Cheers,