Analysis of the Operation of Vacuum Tubes as Class C Amplifiers

The operation of class C amplifiers under carrier and modulated conditions is analyzed with the aid of constant-current charts. With these charts one can precalculate all operating factors such as output, efficiency, and grid driving power. The analysis discloses certain fundamental differences in the behavior of modulated amplifiers connected with self-bias and fixed, or generator bias operation. Audio harmonic distortion traceable directly to the amplifier is discussed in detail, together with methods for "compensating" the grid excitation to eliminate this distortion and to increase the operating efficiency. Oscillograms of the audio relations in modulated class C amplifiers experimentally verify the theoretical conclusions. The problems of grid excitation power, "true" grid dissipation, and "effective" plate dissipation for modulated amplifiers are treated for three tubes differing only in their amplification factors.