The 1938 Pen25 battery output pentode from Mazda was designed for domestic broadcast receivers. The filament was to be run from accumulators and the 0.15 Amp filament current would have assisted in prolonging the accumulator life.
The on-going marketing of the Pen25 is one of Mazda's post-war anachronisms. Not only was it obsolete in concept, since it was oversized compared to the B7G types by then available for all-dry portables and there was little market for new 2 V battery 'household' radios, but it was also fitted with the new Mazda Octal base which made it incompatible with anything else, including the American International Octal which everyone else was using. This was the beginning of a slow decline in the fortunes of the one-time British market leader.