[Arran]

Find out what code number the 48-200 is, it will be something like Code 121 or Code 122, possibly with a run number like #1 or #2 as well, this will tell you which chassis you are working on. As to why there is no sound it could be as simple as a bad tube, it could be an open plate resistor, or even an open primary on the output transformer. Try touching the center lug on the volume control with a screwdriver and see if a hum comes out of the speaker, also try touching the grid pin of the power output tube, there should be a capacitor running between this tube and the 1st audio tube. It's time to break out the volt meter and check the plate and screen voltages on the 1st audio and power output tubes. If the audio section isn't the problem it's time to look elsewhere, it could be an open IF transformer or a non functioning oscillator.
Regards
Arran