I worked for Adcom Inc. 11 Elkins Rd. East Brunswick NJ, from 1992-96, and spent the first 3/4 of my employ as a service tech. This was my first job out of school, and it was as close to a dream job as I could ask for (After all, I went to DeVry just so I could learn how to repair audio and musical electronics). My work was slow but it was so accurate that none of it was ever returned. Eventually, I was asked to check over other tech's work, then I did technical assistance/customer service for a short time until C. Victor Campos took me under his wing for Product Development. I learned a lot and it indirectly put me on an interesting and fulfilling career path.
10 or so years later, Victor and I reconnected, and I went up to Boston to pick up his GFA-585 for repair. He gave me boxes and boxes of gear and paperwork to bring back home. One of those boxes contained the entire contents of my desk from when I worked under him at Adcom!
This is an internal transistor cross reference sheet. These part numbers indicate that the 2nd generation and up GFA-555 used Japanese transistors, while the first gen used US parts. This may be why the 1st generation 555 has a different sound than the later ones.
GFA-555 PRO intro
This is the GFA-555 PRO product info sheet. The pro was made only during the 2nd generation of the GFA-555, and is easily identified by the four circuit breakers and two input level pots on the front panel. This was the only 555 with a balanced input.
This is the GFA-555 PRO schematic.
After a short time as a service tech, I started documenting procedures for other servicing locations. As I look at this, I notice that there is no mention of screw lugs. We were still using solder lug filter caps at the time. The 1st gen 555s used low gauage copper wire for the ground bus - done by hand.
This is the GFP-345 Preamplifier schematic. The GFP-345 was never released in the US - it was for overseas only (as was the GCA-510 Integrated Amplifier; an SLC-505/GFA-535 mashup) and had a phono stage option. It was a decent preamp - somewhere between the GFP-565 and GFP-555 II
Adcom SLC-505. As I recall, this was one of my mentor's babies. This is a simple passive attenuator, but fully functional, including video routing.
GFA-555 II schematic. For some reason, these are not so easy to find online, so here's a big, legible copy. The 555 II is not a Nelson Pass design. This was remade by Walter Morrey with input from C. Victor Campos. This amp is closer to a GFA-565/GFA-585 than a GFA-555.