I just finished a Mesa 400+ amp mod that shuts down pairs of power tubes, with a set of 5 toggle switches. (Thanks to Psycho Bass Guy for all the great info!) It works like this, with all switch's on the amp still puts out 300w. With one switch off max output is reduced to 250w with 2=200w / 3=150w / 4=100w / 5=50w. Each switch cuts cathode ground to a pair of power tubes, basiclly turns them off, and reduces The amps max output by 50 watts. In my research, I learned guitar amp techs have been doing this mod for years. I've only spent an hour playing my amp so far, but this mod does work. At the 50 watt setting, I was able to get a really great saturated tube tone at a low volume. The (switched off tubes) are in stand-by (already warmed-up). When more switches are activated there is no click or popping sound, just a smooth (instant) Increase, in volume and headroom. Here are some pics. (The green wires go to switches). I just could not bring myself to drill any holes in my amp. So I made a switch plate and attached the plate to factory drilled holes. (Edit.) Pics on page 4.