Even though the National Grid came on stream in 1947, the public electricity supply in the UK was a real hotch - potch of AC/DC offered at differing voltages - indeed my own parents came cropper of this in their flat at Arnold Place, Whetley Hill, Bradford as one plug was DC yet another AC resulting in a prized radio going BANG - what a mess!
Little wonder then that 20% of all radios fittted with Mullard valves in the early half of the 1950s were fitted with battery valves. The Mullard battery valve series comprised of five types of valve: -
DL92 - a heptode frequency changer.
DF91 - a vari-mu HF pentode to act as RF or IF amplifier.
DAF91 - a short-grid base pentode t act as AF amplifier combined with a diode detector.
DL92 - an output pentode for portable battery powered receivers.
DL94 - an putput pentode for domestic battery receivers.
All of these valves were designed to be B7G based with a footprint of only 19 x 50mm meaning they were very portable device orientated. The filament current for all types was 50mA @ 1.4V.
These devices were a masterpiece of miniaturisation, allbeit developed from the American 1S & 1T series, these devices meant a freedom from accumulator and mains supplies that "kids of today" take for granted 60 odd year later with their new fangled i-Pod - awww, the ittle darlings..
Eeeeeh, progress tha knows!
A little more on these enigmatic devices in a future blog..................