Total noob here; please assume I don't know anything. (Working on playing-technique is a more a needed priority than studying on technical amp-technique). Sometimes I need more cleans (in volume/headroom) and sometimes I need earlier tube breakup/overdrive. The amps I use are between 5Watts (like SL5, DSL5C) and 50Watts (JCM800). Tried buying multiple amps of the same model and installing lesser/better efficient speakers, or different types of amps (house is full now) but that doesn't work either for me. So if I'd ask my amp-guy to install a switch or pot on my amp (user-controllable on the front like a volume- or gain-knob) to switch/roll between cold bias and hot bias -within reason and safe values-, would that be feasable or reasonable? And if yes, why isn't this a "normal default feature" on tube-amps? I really hate lugging amps around. So, in an ideal world I'd love to have a (one!) 5-15Watt tube amp that can be used both very clean as well as on the edge. (Needed is clean up to 70's classic rock, not going further than AC/DC or ZZ Top).