AUTOMATIC GRID BIAS SUPPLY
The goal of this design is to get a high gain without big average dissipation. With the tetrode like YD1057 it is necessary to bias the tube at 200 mA to obtain a good gain. With 4000 Volts plate voltage, the dissipation is 800 Watts "monstrous". In order to reduce it, the bias voltage is controled by the hf input. In this case the tube is biased only when the high frequency is present in input, otherwise the bias voltage is high to stop the plate current. Of course this design is interresting only with SSB or CW.