In a single-sideband transmitter, which stage allows you to adjust the final transmit frequency?

The Variable Frequency Oscillator (VFO) is the primary component that allows the operator to tune or change the operating frequency of the transmitter. By adjusting the VFO, the local oscillator frequency changes, which dictates the final transmit frequency when mixed with the baseband or intermediate frequency (IF) signal. Other stages like the balanced modulator or sideband filter operate at fixed frequencies within the radio's intermediate stages to process the audio. The antenna tuner is used to match impedance for efficient power transfer, but it does not dictate or change the actual radio frequency being generated.