Pre-war TV RF pre-amps in the UK
 

My question is this: Did the idea of an RF pre-amplifier for use in fringe reception areas of 405 line TV from Alexandra Palace exist before the Second World War?

We are told that the early TV sets were not very sensitive. So when did somebody twig onto the idea of adding an extra outboard RF stage to improve reception for those living in the fringe?

Clearly PYE used the new EF50 valve to market their more sensitive TVs. But instead of using a whole sequence of EF50s - why not just a single EF50 as the first stage followed by lower performance (and probably cheaper) valves? And if that made sense then why not put the EF50 as a stand alone amplifier in front of TV sets that had lower gain as a comparatively cheap way of improving reception in the fringe? Perhaps RF stability of the resulting long TRF amplifier chain was an issue?