Reissue Champion 600
I have modified lots of these great little amps. The two most popular mods are to replace the grillcloth, and to replace the stock speaker with a vintage Jensen or Oxford AlNiCo speaker.
It is also common to raise the gain of the amp, and to change the tone by bringing the tone circuit out of the lower frequencies that the amp can't reproduce, anyway.
This is probably the most amp for your money of anything out there. You can buy these on e-Bay all day for less than $200, and sometimes for less than $100.
It makes a great harp amp.
for more Champion 600s, see my YouTube channel here.