6GW8

The 6GW8/ECL86 combines a high-mu triode and a sharp-cutoff pentode in one envelope. The RCA manual lists it for preamplifier and audio output stages in sound equipment and television receivers. It is a compact way to provide two different functions: the triode handles a small signal, while the pentode can work in the output stage. The sections have separate cathodes and connections, though they share a heater. RCA's sheet dated May 1965 specifies 6.3 V and 0.660 A for the heater; the RCA manual instead lists 0.7 A. The sheet date alone does not establish when the tube was introduced.

The base is nine-pin noval, with RCA 9LZ pinning viewed from below. The triode grid, cathode and plate are on pins 1, 2 and 9 respectively. In the pentode, the screen grid is on pin 3, the plate on 6, the cathode together with the suppressor grid and internal shield on 7, and the control grid on 8; the heater uses pins 4 and 5. The shared connection on pin 7 concerns the pentode elements, not the triode cathode. These details matter in restoration: recognizing two systems in one bulb is not enough to wire them as though they were one section.

RCA gives class A characteristics at 250 V on the plates: with its grid at −1.9 V the triode draws 1.2 mA and has an amplification factor of 100; with 250 V also on its screen grid and −7 V on its control grid, the pentode draws 36 mA at the plate and 6 mA at the screen. These are operating points for the individual sections, not the audio output power of a set. The design-center plate dissipation limits are 0.5 W for the triode and 9 W for the pentode; the stated plate-voltage limit is 300 V for each. The sheet and manual differ on maximum screen-grid input, giving 1.8 and 1.5 W respectively. A particular circuit therefore calls for the applicable documentation, and this limit must not be confused with output power.