845

The 845 is a power triode documented for audio amplification and modulation. An Amperex sheet also presents it as a transmitting tube, but the numerical operating conditions in the sheets consulted here concern audio stages and modulators. The distinction matters: the designation identifies the tube, while output power and operating limits depend on the circuit, operating class and conditions specified by the manufacturer.

The thoriated-tungsten filament directly heats the emitting electrode. RCA and Amperex specify 10 V and 3.25 A for the filament supply and an amplification factor of about 5.3. The base is a four-pin Jumbo type. These figures explain two practical aspects of the 845: its filament needs a substantial dedicated supply, and the socket must suit its construction. Brown Boveri documentation for the T110-1, stated to be equivalent to the international 845 type, calls for mounting vertically with the base down or horizontally with the filament plane vertical.

For class A audio operation, the 1940 RCA sheet gives three examples for a single 845: at 750 V on the anode, about 15 W output with a 3.4 kΩ load; at 1000 V, about 24 W with 6 kΩ; and at 1250 V, about 30 W with 11 kΩ. These are separate operating points, not three interchangeable power figures for the same circuit. The Amperex sheet also gives 15 W at 750 V, but lists 21 and 24 W for its examples at 1000 and 1250 V respectively, with different loads and bias settings. The difference is a useful reminder: interpreting a stated output requires reading the entire operating row, not just the anode voltage.

With two tubes in push-pull, the sheets give examples of class AB amplifiers or modulators. RCA lists about 75 W maximum output at 1000 V on the anodes and about 115 W at 1250 V, specifying that the typical figures apply to the pair; Amperex lists 75 and 105 W in its examples. Brown Boveri also gives push-pull data for two T110-1 triodes. Since manufacturers do not always give the same output at the same voltage, the 845 cannot be reduced to a single nominal output figure. Power delivered to the load must be distinguished from power drawn from the supply and plate dissipation.

The differences also appear in the ratings: RCA specifies a maximum anode voltage of 1250 V and 100 W plate dissipation, while the Amperex sheet retains the 1250 V limit but specifies 75 W dissipation. The T110-1 gives 100 W for the anode. Limits from one sheet must therefore not be substituted automatically for those of another manufacturer's version. When designing or checking equipment, consult the sheet relevant to the actual tube and always distinguish maximum ratings from examples of typical operation.