Combination of the old-style As & Bs. A for the vacuum tube filaments and B for the main power.
Can’t seem to find what the inside of an original B looks like, though; just the modern equivalent with wiring a bunch of 9s in series.
When I took first-year university chemistry back in the dark ages, we went through the chemistry that explained why batteries were all 1.5V (give or take). Apparently lithium-manganese batteries are natively 3V, which is why some button cells are 3V, something I learned recently. But basically, the chemistry determined the voltage. As a result, the batteries designed for assorted devices tend use one or a series of 1.5V cells. Then, the little adapter bricks follow suit and also tend to use multiples of 3V or 1.5V. As mentioned above, this is also convenient for transistor function too.
And I don’t think Mr. Scott is gonna believe you were tryin to make di-lithium either and he’s likely to be kickin yer arse.
