A battery

In electronics, an A battery is any battery used to provide power to the filament of a vacuum tube. It is sometimes colloquially referred to as a "wet battery" (although there's no reason why a "dry" battery of suitable voltage couldn't be utilised for the purpose; the A battery in the photo is a dry battery.) The term comes from the days of valve (tube) radios when it was common practice to use a dry battery for the plate (Anode) voltage and a rechargeable lead/acid "wet" battery for the filament voltage.

The alphabetic designation of these batteries is derived from the historic identification of the elements of the vacuum tube. Initially, the only such device was a diode with only a plate and cathode. Following the direction of electron flow, these electrodes were identified as "A" and "B" for the cathode and anode (plate), respectively. Later, when the control grid element was added to create the triode tube, it was logically assigned the letter "C."

Eveready #742 1½ Volts
Portable "A" Battery for 1.4 Volt receivers
L 2.5" W 2.5" H 4" ca. 1942

The "A" Battery circuit of a Triode (white area)

See also

• B battery (vacuum tubes)
• C battery (vacuum tubes)

External links

• Instructions for Operating The Crosley 51 Radio Receiver Examples of usage of A, B, and C batteries in an early radio.

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