The first thing I would do, especially for an anemic amp, is to replace the filter caps. The orange Mallory dates to 1968 ......over 45 years old. Also replace the multi-section can capacitor. You'll want higher voltage caps due to the higher wall voltage we have today. Lots of vendors will have these....AEC, Mojo, Triode, etc. The power supply has to be working properly for everything else in the amp to do their jobs. Other than tubes, filter caps are the most likely culprit. Do this before you start messing around with coupling caps, transformers, etc.