Fender Champ in an antique Sparton radio cabinet

This is another radio given to me to be converted into a tube guitar amp. The Sparton 410 radio is almost 90 years old and was built in the pre-superheterodyne era. Surprisingly, it had been restored and was somewhat functional—at least, it was making some noise. The original power transformer produced 5V and 2.5V AC and weighed around 10 pounds, so it was replaced with a modern one. I built a classic Champ circuit and integrated a tone pot with the original dial scale. The front panel was reinforced with a plywood plate to support a new 8-inch Jensen speaker.

The amp looks great and is making its owner very happy. 

It all started with an old, rusty, and dusty radio. The big hole on the left was probably for an electrolytic capacitor. Someone had previously worked on restoring the radio, and all the electrolytics had already been swapped for new ones. My first thought was simply to build a new chassis. However, the goal was to keep the original appearance, including the dial mechanism connected to the large variable capacitor in the middle, so I gave the old chassis a try.

All the rust was scrubbed off with a wire brush first. Then, I applied Naval Jelly and washed it with soap. After a couple of rounds, the result was satisfactory, so I dried the chassis and coated it with lacquer to prevent further rust.

The gray cans turned out to be tinned copper. The extra gaps in the chassis were closed with galvanized steel tie plates (I love using those!). All power components were positioned to the left of the big variable capacitor, while the preamp was placed on the right. A modern three-prong power cord was installed along with a couple of fuses. All of the rusty screws were replaced with new, shiny ones.

This is another great-looking radio-style amp. It is affordable, with all components around $200 CAD. It produces a classic warm tube tone, and its gain control pushes it from clean sound to a nice overdrive. With a new Jensen speaker, the amp sounds fantastic.