Some of the BBC Research Department Reports (RDRs) covered aspects of valved UHF TV tuners.
RDRs are available on-line at:
http://downloads.bbc.co.uk/rd/pubs/r...eport-list.pdf.
RDR 1958-13 described tests on an RCA-Victor UHF tuner the regular North American type, with a bandpass input, diode mixer and 6AF4A oscillator.
One of the conclusions was:
“The performance in respect of noise factor and sensitivity is surprisingly uniform over the band. The value of noise factor (15 to 17.5 dB) is quite good for a mass-produced tuner with such a wide frequency range.”
RDR 1958-17 described tests on an NSF combination of a Type 110 VHF turret tuner and a Type 107 UHF adaptor.
The UHF adaptor followed American precepts with a bandpass input, crystal mixer and EC93 oscillator. The EC93 was also known as the 6BS4, but I suspect that the latter was from the RETMA registration of what was a European development, as it the 6BS4 was not mentioned in American articles on UHF tuners and valves that I have seen.
One of the concluding comments was:
“The noise factors measured on the v.h.f. channels are exceptionally good for a standard commercial tuner. On the other hand, the noise factor measured at 650 Mc/s is rather poor, and is at least 3 dB worse than that quoted by the manufacturers.”
The VHF tuner used a PCC88 sharp cutoff frame-grid RF amplifier and a PCF80 oscillator-mixer.
Anyway, from the nature of the NSF combination, one may see that at least one major German manufacture did some early work with the American style of UHF tuner.
RDR 1959-08 covered tests on a couple of UHF amplifying valves, namely the GEC A2521 and the Mullard TDO3-5. The Brimar 6AM4 was mentioned but not tested.
Here an introductory comment was pertinent:
“In superheterodyne receivers the mixer stage is an important source of noise. At lower frequencies the selectivity of a receiver and the signal-to-noise ratio of its output can be improved easily by preceding the mixer stage by a stage of r.f. amplification. At u.h.f. amplification is difficult owing to transit-time effects, and the noise introduced by an amplifier stage becomes comparable with that introduced by the mixer stage. Careful design of the valve and its associated components is therefore necessary to obtain any advantage over the present commonly-used arrangement of a crystal mixer as the first stage.”
Perhaps that was why, in the German case, it was necessary to develop the EC88/PC88 with better performance than the EC86/PC86 for UHF RF amplifier service in order to get the noise factor low enough to justify the two-valve approach to UHF tuners.
Cheers,