A practical compromise is to use two quarter-wave lines connecting to opposite sides of the tube. It is interesting to note that each of the two quarter-wave lines is physically longer than if only one quarter wave line were used. This is because only one-half of the tube output capacitance loads each of the two lines. Variable plate portion of plate-tuning capacitor C3. Details of plate lines L5 and L6.
Copper tubes are standard water pipe.
Output power is coupled from the plate circuit through the series capacitor into a 50-ohm output. The plate choke is visible in the front corner. The 8877 socket is centered on a 6 X 6 subchassis plate. The plate tuning mechanism is shown in fig. This simple apparatus will operate with any variable plate capacitor, providing a back and forth movement of about one inch.