Amplifier builded on top of GU-74B tube, which is used in wideband nontunable amplifiers and for single-sideband power
amplification in stationary and mobile RF equipment. It is useful at full ratings through 250MHz.
The GU-74b tube is generally considered to be similar to the 4CX800A,
although some users report that it acts more like a tube having 900 or 1000W anode dissipation.
For more information see

Input power from 25 to 30 Watt, and output power up to 650 Watt.