Doherty amplifier  The Doherty amplifier is a modified class B radio frequency amplifier invented by William H. Doherty of Bell Telephone Laboratories Inc in 1936. Whereas conventional Class-B amplifiers can clip on high input-signal levels, the Doherty power amplifier can accommodate signals with high peak-to-average power ratios by using two amplifier circuits within the one overall amplifier to accommodate the different signal levels. In this way, the amplifier achieves a high level of linearity while retaining good power efficiency. In Doherty's day, within the Western Electric product line, the eponymous electronic device was operated as a linear amplifier with a driver which was modulated. In the 50,000-watt implementation, the driver was a complete 5,000-watt transmitter which could, if necessary, be operated independently of the Doherty amplifier and the Doherty amplifier was used to raise the 5,000-watt level to the required 50,000-watt level. The amplifier was usually configured as a grounded-cathode, carrier–peak amplifier using two vacuum tubes in parallel connection, one as a class B carrier tube and the other as a class B peak tube (power transistors in modern implementations). The tubes' source (driver) and load (antenna) were split and combined through +90 and −90 degree phase shifting networks. Alternate configurations included a grounded-grid carrier tube and a grounded-cathode peak tube whereby the driver power was effectively passed-through the carrier tube and was added to the resulting output power, but this benefit was more appropriate for the earlier and less efficient triode implementations rather than the later and more efficient tetrode implementations. As successor to Western Electric Company, Inc. (WE) for radio broadcast transmitters, the Doherty concept was considerably refined by Continental Electronics Manufacturing Company of Dallas, Texas (CE). Early Continental Electronics designs, by James O. Weldon and others, retained most of the characteristics of Doherty's amplifier but added medium-level screen-grid modulation of the driver (317B, et al). The ultimate refinement was the high-level screen-grid modulation scheme invented by Joseph B. Sainton. Sainton's 317C series consisted of a class C carrier tube in parallel connection with a class C peak tube. The tubes' source (driver) and load (antenna) were split and combined through +90 and −90 degree phase-shifting networks as in Doherty's amplifier. The unmodulated radio frequency carrier is applied to the control grids of both tubes, and with the same control grid bias points.