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Characteristics of a 201A Vacuum Tube

The 201A vacuum tube, made by the Radio Corporation of America (RCA) and General Electric (GE), was one of the first mass-produced electronic tubes offered, leading to the radio boom of the 1920s. A simple four-pin triode, it served as a power amplifier, boosting signals carrying music and speech until they were strong enough to drive a loudspeaker.

Configuration
- The 201A is a tride tube, meaning it has three main elements: a filament or cathode, a plate or anode, and a grid. The 201A had a pear-shaped glass bulb containing the electronic parts and a brass base surrounding a ceramic insert with four metal pins that connected to a socket in the radio. Its filament is made of tungsten, which can take very high temperatures without melting. The tungsten has traces of thorium, a slightly radioactive metal that makes helps the tube produce electric currents more efficiently.
Current and Voltage
- The tube's filament ran on 5 volts at 0.25 amps of current. The plate (anode) ran at a maximum of 135 volts. To be used as an amplifier, the grid should have a negative bias of between 0.5 to 3 volts.
Variations
- The tube received several minor changes over the course of its production. Early tubes had a sealed glass tip at the top of the bulb left over from the vacuum process. This was eliminated in later years. In 1925, manufacturers replaced the brass base with one made of an early plastic, bakelite.

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