6AN8A

The 6AN8A combines a medium-mu triode and a sharp-cutoff pentode in a nine-pin miniature envelope. Tung-Sol and Sylvania documentation proposes it for television circuits: the pentode can amplify intermediate-frequency or video signals and serve as a reactance tube; the triode suits low-frequency oscillators, sync separators and clippers, or phase splitters. The two sections allow different functions in one component, but each has its own pins and operating conditions. The heater requires 6.3 V and 0.45 A; the A version has a controlled warm-up time intended to limit voltage surges in series-heater circuits when the other tubes have compatible characteristics as well.

A class-A operating example makes the difference between the two sections clear. The RCA and Tung-Sol sheets give, for the triode, a 150 V plate supply, a grid at −3 V, about 15 mA plate current, about 4.7 kΩ plate resistance and 4.5 mA/V transconductance. For the pentode, with 125 V plate and screen supplies and a 56 Ω cathode resistor, the figures are about 12 mA plate current, 3.8 mA screen current and 7.8 mA/V transconductance. These are test operating points, not values obtainable together in every set. The small inter-section coupling capacitances listed in the datasheets are especially useful when assessing isolation with triode and pentode working in the same circuit.

The design maximum ratings are separate from typical operating points: RCA and Tung-Sol sheets give 330 V as the plate-voltage limit for each section, 2.8 W dissipation for the triode and 2.3 W for the pentode. For the pentode screen they give 0.55 W as the dissipation limit; the permissible voltage also requires consulting the screen input rating chart. The peak heater-to-cathode limit is 200 V, but when the heater is positive its DC component must not exceed 100 V. A grid-circuit note further specifies that, if either section operates at its maximum ratings, the grid resistances of both must remain within the stated limits. Restoration therefore calls for checking the whole bias network rather than treating the sections as independent in every respect.