This article is a recent contribution from Chrisitian Steingruber, who was an early "modifier" of the Quad 405.

Scroll to the bottom of the article to see historical correspondence between Christian and Steve McCormack.  (Soldering iron burns in the paper left in for authenticity)

"My first amplifier for driving the 57' was the Quad 405. It was a very stable amp, which I also used in our recording studio,  but soundwise it was a little shut in. As a subscriber of the 'The Absolute Sound' mag I heard of a special modification by Steve McCormack. I bought the kit ... and I was very surprised, how much better the 405 sounded after the mod. I think it could compete with the best amps of this time (e.g. Mark Levinson, Audio Research).   [ Christian Steingruber]