Re: When did Valve heaters change from 4v to 6.3v
4v is for a two-cell lead-acid battery, running alone.
6.3v is for a three-cell battery with a dynamo charging it.
The former fits users who took their accumulator along to the bicycle shop every week to get it charged. The latter fits the car radio market. Valve makers went to 6.3v heaters when they thought there was a hope of selling some for car radios in their part of the world. 4v valves had gone from direct heated to insulated cathodes when mains sets appeared.
America had the lead in 6.3v valves because the greater wealth over there meant cars were more common sooner.
Our military wanted 6..3v for mobile comms.
The move to 6.3v was not a sharp change, it spread across the later thirties and WWII hammered it home.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
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