The B battery supplies the positive voltage to the anode (plate) of a thermionic valve, driving the electron flow across the vacuum. In early radio sets, this voltage was typically between 22 and 90 volts, much higher than the voltage used to heat the filament. It was usually made of many smaller dry cells wired in series.
Heard on the job
We need a 45-volt B battery to get this old tube radio working again.
Insider tip
You will almost never see a true B battery manufactured, so restorers usually wire a string of 9-volt batteries in series to recreate the high voltage.
Also heard as
- plate battery
Do not mix it up with
- A battery: The A battery heats the filament, while the B battery provides the high plate voltage.