In operation, the U end acts as a coupling link and is held near the transmitter's tank coil, and the shorting bar is slid out along the arms until the transmitter's plate current dips, indicating the first node has been reached.
22.
A sufficiently negative voltage on the grid, usually around 3-5 volts in small tubes such as the 6AV6, but as much as 130 volts in early audio power devices such as the'45, will prevent any electrons from getting through to the plate, turning off the plate current.
23.
As long as the control grid is negative relative to the cathode, essentially no current flows into it, yet a change of several volts on the control grid is sufficient to make a large difference in the plate current, possibly changing the output by hundreds of volts ( depending on the circuit ).
