Every time I do a hacking workshop in Europe students bring in these great old radios from the 1960s and 70s for the "laying of hands" project (transforming a radio into a Cracklebox.) Some of the best are by Grundig, so I started picking up a few on eBay when I can snag them for less than my $20- limit. A 1960-vintage "Transistor Box 60" arrived with a busted tuner section, and it turned out to be not so useful as a Cracklebox. I removed the tuner circuit board from one side of the box and replaced it with a classy Neutrik jack from my parts bin that fit perfectly in the cutout from the tuning knob; this became the new input to the amplifier circuit. I ended up with a really cute mini-amp, with great sound: just a few transistors (no ICs); and the amp couples to the speaker through an output transformer, just like a good old guitar amp. The internal slide switch bypasses the amplifier when I want to power the really sweet vintage speaker from an external amplifier. Conversely, the second jack is for adding driving an external speaker or headphones from the Grundig amp, or for using the circuit as an overdrive pedal.

(Scroll down for all three photos.)