Good morning, Jolidafan:
Not sure if this is much help. I have a SJ502 (that predates most of the 502s) in which most parts were replaced with same size/rating ones and small mods done. Before the refurbishment, warm and lacking some detail (including imaging, soundstaging, and bass) After the refurbishment, still warm but clearer, more detailed, etc. Also using KT120s which provide a little more or everything.
1. All resistors replaced including the bias pots. The ones across the tube sockets pins (can't remember what the term is called (cathode resistor?) as I'm not that technical) were replaced with higher value and wattage ones. The bias pots, which were ordered through Jolida USA, were replaced because of the limited range/travel or failing original ones
2. All caps replaced (including the ones in the power supply). The coupling caps (.22uf & .47uf) were replaced with Obbligato Golds.
3. Power supply diodes were replaced with Hexfreds (Fairchilds or Shottkys?) (Been a while and memory isn't like it used to be.)
3. Volume, balance, and and selector contols were not replaced (given the limited space) as it was wired to be used as a power amp instead (and easily reverted back by soldering couple (or was it four, the other two from the RCA jacks) of wires).
4. Some of the wires were replaced with Cardas hook up wire.
5. RCAs were replaced with Neutrik ones
6. Gold plated metal (brass?) binding posts replaced with nicer gold plated and insulated ones (had to drill larger holes to accommodate them).
By the way, is it Dave Ellis (Ellis Audio) and not Dave Harris? I used his guide when working on my unit...
http://www.ellisaudio.com/jolidamods.pdfSincerely,
Kingsley.