A battery (vacuum tubes)

From Wikipedia, the free encyclopedia

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.