Thinking inside the box...

This sounds like an awesome project. I also have some of these boxes laying around and would appreciate if you would share this build with us.

 

I would say that they'd be a great contender for the Firefly and other low-wattage projects to be found over at AX84.com. I've always been interested in building some of those, and I happen to have a modest stash of nice cigar boxes too. I think it's a great idea! It'll go in line right behind that spring reverb I've been wanting to build.

As to speakers I really don't think they make many speakers in that size range that would be particularly good for guitar. I'd hit up garage sales and look for bookshelf speakers in that range. They won't be perfect, but they might add mojo of their own.

 

You'd be surprised how well small speakers work for small amps. I've been using vintage alnico 6x9s in Champs lately. They're bright little speakers. I expect a Princeton or a Deluxe would sound lousy through one and at the same time it would be more amp than the speaker could handle. It turns out they're one of those "Where have you been all my life?!" tones in a Champ.

A tweed Champ gets thicker and darker as you turn it up. A brighter speaker combined with a dark amp is a perfect combination. An added "bonus" is that the 6x9s break up almost instantly. The net effect sounds like a cranked Super Lead with tormented 25 watt Greenbacks, I get overdrive and singing sustain you'd swear came from three or four gain stages with an overdrive in front. No pedals, two 12AX7 sections... and with a Telecaster!

BF and SF Champs won't scream like tweeds.

 

check out old car speakers available at junkyards everywhere !!! old Alamo, Gretsch etc used car speakers (6x9)

 

Bits one of these, or similar -

 

I've been getting mine from a TV repair shop. TV's that can't be repaired usually have decent speakers. Cost is usually cheap of free.

 

Here's a few to consider for your amp circuit question.

http://www.runoffgroove.com/littlegem.html

http://www.runoffgroove.com/ruby.html

http://www.runoffgroove.com/grace.html