I have often heard people say that after a while the sound from the small internal loudspeaker in an RA17 sets their teeth on edge.

Firstly, the loudspeaker was only ever intended as a monitor; hence the ability to switch it off. However, quite comfortable audio during AM reception can be achieved using the following procedure:-

Set the System Switch to AVC and run with the volume up as high as you dare (maybe 90%) and control the audio level with the RF/IF gain control. If you have one of my refurbished sets, the overall noise level will be so low as to permit a higher level of audio gain. Essentially the base response of the audio stage increases as the volume control is turned clock-wise. (Note: This will not necessarily work with the RA17W  which has its RF/IF Gain control disabled when AVC is selected). If you still have distorted audio from the front panel loudspeaker, it is very likely that the cone is torn or there is debris behind the grill interfering with the cone.

Miscellaneous:

AVC (Short/Long) Switch: Only functions when System switch is set to AVC. Sets the AVC time constant.
LIMITER: Supposed to remove noise spikes. Maybe it does, but in the absence of such noise I find it introduces distortion.
METER Switch: In the AF position the meter indicates the audio level at one of the rear panel 600-ohm outputs. This can be set via the AF Level control to the left of the volume control. You will find that SSB audio is much higher than AM audio.
METER Switch: In  the RF position the meter indicates the level of detector current which is why it goes to about 75% deflection when the BFO is on.

To operate the Calibrator, set the System Switch to CAL. Calibration heterodynes will be heard every 100KHz. Use this to calibrate the film-scale by sliding the cursor to coincide with the nearest multiple of 100KHz.

The final setting on the System Switch is for calibration of the BFO. Select Check BFO and set the BFO on. A heterodyne will be heard which is not dependent on the KHz setting on the film-scale. Rotate the BFO knob such that the note drops to 0Hz. Then either slacken off the cursor and align it on zero or set it to zero and adjust the BFO via the internal adjustment.