If you know your way around a multi-meter i would just take the amp part apart and start to measure Every resistor, cap, etc, to make sure everything is within specs and replace whats bad. I know vacuum tubes need to be dial in with another device made specific for that, don't know the name. Once all the electronic parts are sorted out you can start working with the mechanical parts, like the arm and all. You might need a new stylus for the turntable, but maybe a good cleaning will do. I Work with guitar electronics and amps as a hobby, but never dealt with a radio from that period.