The 6S4A is a 9-pin miniature medium-mu single power triode designed for vertical deflection oscillator and amplifier service in television receivers. Featuring high plate current capabilities at low plate voltages and an 8.5W max plate dissipation, it is also utilized in audio driver stages, linestages, and electrostatic headphone amplifiers. The "A" suffix denotes an upgraded design with controlled heater warm-up time. It operates on a 6.3V heater and fits standard 9-pin noval sockets. Available NOS and tested used.