Here is a really great explanation of how these little amps work:
This guy is more concerned with the visual aesthetics of the caps than the actual function. He never even checked the Sangamos, or the bias resistor. While the amp certainly works, is it really 'vintage tone' or 'worn-out tone'?
Danelectro is my favorite type of guitar, simply for the genius of their unorthodox, inexpensive, yet highly effective designs. I love the tone of old-growth masonite. If you are looking for details, the Pro-1 Bass is the most complete build documentation.
More: Danelectro Projects ...
I only use clip-less battery boxes for two reasons. First, those 9-volt battery clips may be tolerable for a smoke detector, but if you plan to use it a lot, it is a pain in the ass, and then it breaks. And second, 9-volt batteries ( all batteries, really, but especially 9-volts ) are guaranteed to leak, and should never be left inside a device unless absolutely necessary. I only put a battery in a guitar ( or anything else ) when I want to use it, and then take it out afterward and keep it in a little dish. That's much easier if it just slips in and out and you don't have to mess with one of those stupid clips. And if when it leaks, I just throw it away and wash out the dish.
More: Batteries ...