Ferguson 391T Radiogram

[ppppenguin]

The use of the PCF80 rather than the ECF80 is hard to rationalize, given that the ECF80 was a common and abundant valve type, and had a 100-volt heater-to-cathode rating.  Possibly there was an element of chronology, in that in the 1950s Philips was inclined to introduce P-type TV valves ahead of their E-counterparts.  But the ECF80 was certainly used in some of the first crop of UK FM receivers, so it would have been available to designers during 1954 at least.

I agree that it's hard to see a reason, apart from my earlier suggestion that Ferguson had plenty of PCF80 available from their TV production but were not otherwise using ECF80. So they thought it was cheaper to put an extra tap on the transformer than to stock another different type of valve. Or possibly the ECF80 might have been in short supply at the time of the design and it wasn't worth changing to it later.