CLASSIFICATION – Moderate power, filamentary triodes for class-A service.

APPLICATION – Audio-frequency amplifier in positions where power outputs of approximately ten watts or less are required at relatively low plate voltages.

BASE AND MOUNTING – These vacuum tubes employ medium, four-pin thrust type bases suitable for use in Western Electric 143B or similar sockets. The 300-B tube has the bayonet pin so located that it may also be mounted in a Western Electric 100M, 115B or similar socket. The tubes may be mounted in either a vertical or horizontal position. If mounted in a horizontal position, the plane of the filament, should be vertical.

AVERAGE DIRECT INTERELECTRODE CAPACITANCES – Grid to plate 15 μμf. Grid to filament 9 μμf. Plate to filament 4.3 μμf.

FILAMENT RATING – Filament voltage 5.0 volts, AC or DC. Nominal filament current 1.2 amperes. The filaments of these tubes are designed to operate on a voltage basis and should be operated at as near the rated voltage as possible. When alternating current is used for heating the filament, the grid and plate returns should be connected to a center tap on the secondary of the filament transformer.

CHARACTERISTICS OF THE 300-B VACUUM TUBE AVERAGE CHARACTERISTICS – (Ef = 5.0 volts, a.c., Eb = 300 volts and Ec = -61 volts), Plate current 60 milliamperes, Amplification factor 3.85, Plate resistance 700 ohms, Grid to plate transconductance 5500 micromhos.