The Music Master STD 5B was manufactured by Melhuish Radio Co. in about 1963.
4- or 5-valve broadcast mantle set. Appears to be similar in style to the sets of the post-war decade but the year is a guess based on the serial number and certainly not in line with its appearance (although the ARTS&P label shows it being some time from 1955 onwards). As seen for sale, no further details.
Valves (4 or 5?): 6AQ5 output?
Chassis Notes (most schematics can be clicked to download a full size version): This was probably quite a late 4 or 5 (or 4 with solid state rectifier?) model in the valve era. Serial number suggests 1963 which seems a little late.