There’s a mod you can do to plexi-style amps called the “one wire” mod.  Basically, you move one wire in the amp to change the two parallel input stages into a single cascaded input stage (making it more like a JCM800).  In practice it is a little more complicated to reverse than what Rachel is doing here (it would require a little resoldering and potentially repurposing one of the volume knobs as a master volume), but, you know, then the joke wouldn’t work very well. 🙂