I remember when there were no radios that operated on alternating current, in fact I can remember when there were no radios at all. However, at the time that I first became interested in such things, most all radios got their six volt tube filament supply from a wet cell battery, just like the one in your car, only six volts instead of twelve. Dodge cars were the only ones that used twelve volt batteries, at that time. This wet battery was known as the "A" battery.
The voltage for the plate in the tubes came from a dry cell battery at either 45 or 90 volts, and sometimes even 135 volts. These were known as "B" batteries.
In due time there was a vacuum tube (triode) developed that had three elements, a filament (heater), a plate and a control grid. That grid required another voltage supply which was supplied by a "C" battery. I don't remember for sure, but I think that the grids required nine volts. The "C" battery was a dry cell type, because there was not a great amount of current required. ii
Keep in mind now, all of these batteries were stowed in close proximity to the receiver, usually on the living room floor, right behind the set. It didn't take long for someone to come up with a better "mouse trap", which turned out to be a Battery Eliminator. This was nothing more than a rectifier which took care of the six volt requirements, but still left the "B" and the "C" batteries behind the table that held the receiver, the big horned speaker, the ash tray and the Log Book that was always kept to prove that you had not only received KDKA East Pittsburg, but you had also received KFI Los Angles.
I suppose that, in the natural course of events, it could have been predicted that someone would come up with a #80 Diode tube that could rectify Alternating Current to Direct Current. That was done after the voltage had been raised to 450 volts, by a transformer whose secondary was tapped to provide the six volts of Alternating Current that the tube filaments required. The 450 volts of direct current was applied to the tube plates. I guess that I never did know where the grid voltage came from because, by that time I was interested in other things.
That combination of the transformer and the #80 rectifier tube, along with the 01A, the 35Z5 and several more of the old stand-by tubes, took care of things for a good while. But then, after several more changes, such as putting the tube filaments (heaters) in series, some smart-ass came up with a Transistor and wiped the vacuum tube right out of existence.
The introduction of the transistor was a real blow to the radio service man, because it then became cheaper to throw the old set away and buy a new one than it was to have the old one repaired. However, there were a lot of die-hards that just could not accept a radio that didn't have tubes in it, the same as there are people today that will not let themselves believe that a Word Processor can do a better job, and do it faster and easier than a typewriter.
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