Jason FM/TV sound tuner

[ppppenguin]

A full breakdown of the ECF80 code is:

E = 6.3V heater
C = triode
F = pentode
80 = B9A base

Strictly speaking 8 = B9A base. The 0 is an arbitrary designation by the manufacturer to distinguish between different 6.3V triode pentodes on B9A bases.

It was probably sensible for Jason to use 6.3V parallel heaters for their tuners. A live chassis approach would have been impractical though they could have used P series valves with a suitable winding on the mains transformer to supply the total heater voltage. I suppose they designed their tuners as an adjunct to their amplifiers such as the J2-10. The amps used 6.3V heaters so that's what the designers were familiar with.