6AG7

The 6AG7 is a metal-envelope power pentode developed chiefly for the output stage of television receivers' video amplifiers. An RCA document from 1939 also describes its use as a coupling device in transmitters: its high transconductance and plate-current capability allow a substantial voltage swing across the relatively low load needed for wide-band video. The heater requires 6.3 V at 0.65 A.

The base is a small eight-pin octal type. In the General Electric sheet's pinout, pins 2 and 7 feed the heater, pin 4 is the control grid, pin 5 the cathode, pin 6 the screen grid, and pin 8 the plate; pin 1 connects to the metal shell and suppressor grid. For pin 3, however, the early RCA sheet specifies an internal shield to be grounded, while the later General Electric sheet marks it as no connection. Check this documentary difference against the sheet for the maker and specimen before using a socket contact as a wiring point.

The General Electric sheet also gives a Class A audio-frequency amplifier example: at 300 V on the plate, 150 V on the screen grid and −3 V control-grid bias, it specifies about 30 mA of quiescent plate current, a 10 kΩ load, and 3 W output at 7% total harmonic distortion. These are figures for that operating point, not the tube's maximum ratings.

For a video amplifier with 4 MHz bandwidth, the same sheet instead gives two circuits with a 300 V plate supply and a 3.5 kΩ load: with grid-resistor bias, a 115 V screen and about 135 V peak-to-peak output; with cathode-resistor bias, a 125 V screen and about 140 V peak-to-peak. General Electric's design-center limits are separate from these examples: maxima of 300 V on the plate and screen grid, 9 W plate dissipation, and 1.5 W screen-grid dissipation. In restoration, check voltages, dissipations, and pin connections against the applicable sheet.