The Vox AC15CH has a built in attenuator that will take the 15w down to either 1.5w or 0.15w. Nowhere do I see a warning that you should not set it at either of the lower settings and crank it (same with the Marshall Origin attenuators and with Carr or Tone King and their built-in attenuators). However, reading about the Weber MiniMass 50w attenuator (or other brands) online, there are plenty of warnings about not cranking the amp while heavily attenuating the power. For example, from the Weber site (unclear if this only applied to high gain amps) regarding the MiniMass50. "Do not turn your amp all the way up. Even if you’re just knocking a little off the top with the attenuator, it’s a good idea to keep the amp somewhere in the middle at most. It’s best to find the lowest volume on the amp that is the acceptable tone to you, and then use the attenuator to bring it the rest of the way." Is there something Marshall and Vox are doing that Weber and Dr. Z, etc. are not doing in the attenuation? Is the issue simply that cranking the amp puts the same stress on the amp that cranking the amp without the attenuator? Even with the Vox or Marshall, should attenuation be moderately used. I have a Carr Skylark, and every once in a while I like to max the volume and attenuate it down to about 1w. It's an expensive amp, I don't want to kill it!