The 5020 is s Zaurie power supply model that was heavily pushed / reviewed in early 1970s. I got mine in 1978, used, from a garage sale. Heavily abused, and if memory serves, used a selenium stack for rectifiers. May be getting mixed up with another supply. Hard to remember 40+ years ago.
How many 6.3 windings are present on transformer? Mine had 3, i think, and were used to make an aux high voltage output.
~SD
