Little Red Devil Amplifier Looks as Good as It Sounds While Still Being Built on a Budget

When tasked by a customer to create an amplifier that looks as good as it sounds, Keri Szafir rose to the occasion. Szafir, a vintage audio gear enthusiast, achieved both goals while building the Little Red Devil tube amplifier using parts on hand.

The Little Red Devil is a single-ended Class-A amplifier built around an EL84 vacuum tube. If the EL84 does not sound familiar, you might know it as the 6Bq5. These tubes have a combination of price, power level, and sound quality, making them a favorite in amplifier designs. Even with the previously-used EL84 tube, the Little Red Devil produces an output power of eight watts.

Szafir aimed for a constraint of not drilling any extra holes in the enclosure. One example of avoiding additional holes comes from the remote control. The end user can train the amplifier to a specific remote's buttons for maximum flexibility. However, this feature means the ATtiny45 needs to go into a "programming mode." Instead of drilling a hole and mounting a button, Szafir used a reed relay. Now the end-user can place a magnet near the reed switch to activate the programming mode!

While many projects we feature involve printed circuit boards or protoboards, the Little Red Devil has era-appropriate point-to-point wiring. That small detail adds a bit of charm since this amplifier also accepts audio Bluetooth signals!

One unique build decision involves the power supply. It is an external box from the amplifier circuit. It contains the transformers and control circuit. It gives the Little Red Devil's tube section a compact look while still delivering an audio punch.

While the project page write-up is a good description, Szafir created a set of YouTube videos before shipping the amplifier to the customer. The video above is an excellent overview of the amplifier and its hand-drawn schematic. And for even more detail, here is the full story behind creating the Little Red Devil.