Well, all the early Roberts radios were good quality, performed and sounded well.
The little green R66 was a nice little set. The usual 7 pin “D” 1.5 volt and 90 volt range of vales were used. The set had a mains supply built in. Generally all is okay with these sets and the components did not have to suffer high HT stress and hardly any heat was generated. The main problem I seem to come across is to do with the LT rectifier. These little selenium devices fall to bits and or go high resistance, staving the valves of the 1.5 volt heater supply. Change this for a modern device and away you go.
The later sets being solid state used the more traditional battery supply. 2 X PP9s. Sometimes these were wired in series, other times, the supply was split and drove different parts of the set. A good size loudspeaker was used and with plenty of power from the germanium output transistors, these portables put many big sets to shame.
One annoying thing with Roberts sets, as for Hacker also (same chief engineer), the RF sections were “canned”. This made repairing awkward when confronted with a RF fault. You had to dismantle half the set the get the module out so that you could carry out you favourite AF116 bodge (for those of you that know what I mean).