Thanks for the pics! I've never had the pleasure of listening to a MC3500 let alone have one come across my bench.
The closest I've come was helping a fellow who came to AK looking for help in servicing one. Seems one bank of output tubes would virtually red plate shortly after turn on until the 6BL7 driver tube would finally settle down after warming up and play nice. He had tried multiple replacement tubes for that position, but all were giving him the same problem. Apparently, Mac originally used specially preselected 6BL7 tubes that were more socially acceptable for the design, but of course were no longer available. All of his NOS/NIB but still garden variety 6BL7s simply wouldn't operate correctly in the amplifier. I suggested a modification for him to make to the driver stage that would allow it to operate properly with any 6BL7 that came down the pike original or otherwise, which he reported cleared the problem right away -- but that's as close as I've ever come to being involved with one.
Really appreciate the pics. There are just so many things that amplifier did beyond simply powering Woodstock. It forever married Frank and Gordon's classical music appeal to the new wave of pop music that was taking over, and was instrumental in the new way it would be forever presented to live audiances from that time on. In helping the company make that turn, it also helped ensure that McIntosh would still be going strong today 55 years later, when so many other classic names of that day couldn't make the turn, and are either long gone or irrelevant. Of course, the MC275 accomplished much the same thing on the field it played on. When it comes to amplifiers, I don't know how it gets anymore iconic than that.....
Dave
