Class B Amplifiers Considered from the Conventional Class a Standpoint

The wave form of the output current of an ideal tube is analyzed when plate current cut-off occurs between zero and 180 degrees of the cycle. The theory thus developed is applied to practical tubes, and it is shown that one of the tubes operated in series may be represented as a hypothetical class A amplifier provided that twice the plate load resistance cuts off the plate current for the input voltage used. It is also shown that a diagram may be constructed from the characteristics of a tube for any operating condition from class A to class B with half the wave cut off. The load resistance used may then be transferred back to the characteristic. This load resistance shows conditions under which each tube is operating and explains why it is possible to obtain more than twice the power output under some conditions with two tubes than with one tube under the same conditions.