In the early days of electronics, devices that used vacuum tubes (called valves in British contexts), such as radios, were powered by batteries. Each battery had a different designation depending on which tube element it was associated with.
In the early days of electronics, devices that used vacuum tubes (called valves in British contexts), such as radios, were powered by batteries. Each battery had a different designation depending on which tube element it was associated with.
Source: Wikipedia "Vacuum tube battery" · CC BY-SA 4.0
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