[Pieter H]

Thanks a lot for your inputs, the picture is getting clearer.

So the Philips tuner organization at large made the switch from PCC84 to PCC88 in 1956, which required a re-arrangement of the valve socket connection. However, with the socket rotated 180 degrees the connections were roughly identical, so in that respect the effort was limited. But the benefit was considerable, as John pointed out, due to the almost doubled effective gain of the frame grid construction. When the PCC88 was replaced by the pin-compatible PCC189 that was an almost drop-in replacement. This switch-over was made in 1960.

I agree that it's difficult to judge why the Mitcham tuners stayed with the PCC84 for another 3 years. Every TV standard, irrespective of the channel bandwidth, should have benefited from the improved valve. So the most plausible explanation is an economic one. The UK Philips sets had stayed relatively long, compared to the continent, with single channel non-tunable front ends, the first tuner-equipped family being the 1446/1746/1747 in 1954, three years behind the Netherlands and Germany. Given the modest initial volumes it is not unreasonable to assume that in 1956 the first generation investments were not yet written off and a conversion to the PCC88 not justifiable. A "thin" explanation, I admit, but for lack of a better one.

But even then it is difficult to understand why the Mitcham tuners even stayed with the PCC89, because that valve, like the PCC84, had the screen connected to the second gate. In the PCC88 and PCC189 the screen had a separate pin for direct grounding, which was in principle more effective. So a follow-up question: did the UK tuners stay with the PCC89 or did they also switch over to the PCC189, and if so when?

Cheers, Pieter