I have a 1974 100 watt Super Lead that I bought back around 93' or 94'. Over the years I tried every type of master volume and must have taken them out & re-installed them 10 times by now. Right now I have a Lar mar PPIMV installed & I'm using it along with an Attenuator. When comparing the sound at different master volume settings, the amp sounds no different with the master set at 4 and cranked (out of circuit, same as stock). As I turn the master from about 4 to all the way up, the sound is EXACTLY the same. The only thing I notice is the the Presence control starts to work at about half way maybe? So why use the attenuator? I don't hear any magical output tube distortion start to kick in as I turn the master all the way up. Just sharing some observations.