The Penta Laboratories 3-500ZG is a high-mu power triode with a maximum plate dissipation rating of 500 watts. Cooling is by radiation and forced air through the base, along the envelope, and over the plate seal and radiator-type plate connector. It is intended for use as a zero-bias Class AB2 amplifier in radio-frequency or audio frequency applications. By eliminating the bias supply, zero grid bias operation greatly simplifies circuitry design. When operated in a cathode-driven circuit, a power gain of as much twenty times is achievable.