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.
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There are two components to intonation. The first is simple - locating the bridge at the right spot. You'd think that would be obvious, you'd be surprised how often it is gotten wrong. Like my Rickenbacker. The second part is the additional length or 'compensation' needed for each string beyond the scale length. That derives from the string's mechanical resistance to bending, or its stiffness, which is proportional to its diameter. That's why the low fat strings need more compensation than the thinner ones - shortening the string increases its relative stiffness, or the ratio of diameter to length, and causes it to go sharp as you go up the neck. I have never seen a negative compensation, I think theoretically it should not exist.
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