Re: When did Valve heaters change from 4v to 6.3v
Hello,
Early American mains valves were usually 2.5V heaters but this changed to 6.3V with UX or UY bases in the early 30s and then with octal bases in the mid 30s.
In Europe Philips brought out 6.3V valves (EK1, EL1, EZ1 etc) in 1934 but Mullard did not introduce later versions of these in the UK until about 1938. Octal versions of these became available between 1938 to 1940.
In the UK Marconi-Osram produced 6.3V versions of its 4V valves with octal bases in 1937-8. At the same time its high current rectifiers (U50 and U52) changed to 5V with an octal base but its low current rectifier the U10 with a 4V heater and B4 base carried on till the early 1950s.
Mazda brought out its Mazda-octal based valves (TH41, Pen45 etc) in 1938 but they retained 4V heaters and again carried on till the late 1940s to early 1950s. During the war Mazda did bring out some 6.3V versions of its 4V valves (SP61, P61 etc) for military use.
Mazda did bring out the Pen/DD61, a 6V version of the AC2/PenDD for Philco circa 1936.
Yours, Richard
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