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Retro Radio Amp

I saw on CB Gitty's site (good source for Cigar Box Guitar parts) that someone had made a guitar from a lunchbox that looked like an old portable radio. I went to eBay and sure enough, there were a few of these lunch boxes for sale. I got one to make an amplifier out of.

The box only looked like it had a speaker grill in it, so I used a Dremel to carve out some slots to let the sound out. That was a real pain with some unwanted bending of the slats and a lot of scorching. I ended up bending the slats back as best as I could and covering the scorch marks with a red Sharpie.

I used a 5" x 7" speaker that I got on eBay which used to be in a Sony TV. I then drilled holes for all the knobs and jacks that come with my favorite 2.5 watt solid state amplifier. After hooking up the amp and the speaker and mounting them in the box, I found I was getting no sound. If I removed either the amp or the speaker from the box, it would work. Figured out it was the speaker which was designed so the the ground lead coming into the speaker was also grounded to the speaker chassis. With the metal lunch box, this was then sharing a ground with the amp which was shorting out the circuit. I had to buy some nylon screws, washers and nuts to mount the speaker and fix the problem.

The final challenge with this was the handle. It was designed to extend/retract and pivot like a real radio handle, which of course made a tremendous rattling when playing anything through the amp. But that's why God inspired humans to invent Super Glue.

In the end, it made a nice amp for a 5x7 with pretty clear and punchy sound due to the metal box.

Amplifier: 2.5 watts solid state

Controls: Volume, Gain, Tone

Speaker: 5" x 7" 8 ohm 10 watts

Inputs: 1/4" guitar in, 1/8" auxiliary in

Outputs: 1/8 headphone out

Power supply: 9v battery

Dimensions: 7-1/2" height (without handle) x 10" width x 4" depth (without knobs)



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