I also admire the de Rosa style and the de Rosa ride, but as with many other brands we could name, the older ones had better workmanship. I think the brazing carousel was the downfall of de Rosa quality - and for every other builder that used a carousel too.
I've seen maybe 5 de Rosas with the paint off (in for repaint), and on 2 of them the seat lug was about half brazed. Small sample size indeed, but a seat lug with no brass at all around half of the seat tube pocket AND the top tube pocket - that should NEVER happen - yet I've seen two. I just can't imagine that happening except in a carousel environment.
With the brazing carousel, the guy brazing the seat lugs has to finish in the same amount of time as the guys doing the top lugs and down lugs. When the frame moves on to the next station, if you're not done, tough! I'm sure the seat lug guy can yell to whoever is controlling the carousel "hey wait I'm not done yet", but how many times is he going to admit he's too slow (and risk getting fired?). There's a big tendency to just let it go. Also the concentration required is immense; speed up the process, and make it super repetitive (no top or down lugs or BBs to relieve the tedium) and there's bound to be lapses in concentration.
I don't know when de Rosa went to carousel brazing - I'm guessing late 80s-early 90s? Individual frames after that point might be superlative, but I'm afraid the average quality had to have gone down.
There are advantages to brazing quickly - the steel is damaged not just from peak temperature, but also time-at-temperature, so a technique that makes the heat cycle shorter is usually a good thing. The trick is to avoid "burn-out" of the brazer.
I made forks on a carousel at Davidson, but it was just two guys, and the brazer had control of when the carousel moved on - the other guy was just a fluxer/loader/unloader. That was actually fun, and making the forks faster made them better forks. When Bill started talking about a frame carousel though, he practically had a mutiny on his hands - all the brazers hated the idea. Luckily he never got one - I think he knew quality would suffer, and he cared more about quality than quantity, bless him.
I downloaded this video of the Colnago frame carousel, I forget where, but
you can get it off my server if you want at
http://bulgier.net/
Mark Bulgier
Seattle, Wa USA