The 27GB5/PL500 is an air cooled, glass enveloped, octal-base beam tetrode vacuum tube. It was originally manufactured by the Tung-Sol company and is used in high frequency applications. It has a plate voltage of 500 volts, an average plate current of 1 amp, and a plate resistance of 19k ohms. This tube is particularly well suited for use in RF amplifiers, oscillators, and other high-frequency circuits due to its low noise, low distortion characteristics, and high conductance.