A 1955 tube amplifier built on baking trays

Tube audio has a reputation problem. Too often it gets taken over by people who care more about bragging rights than about the fun of building the thing, so it was refreshing to read about a project that goes the other way.

Bettina Neumryr specialises in building circuits from old electronics magazines, and her latest is a tube amplifier from 1955. Hackaday calls it a fantastic antidote to the gold-plated silliness of audiophile tube amps, and I can see why.

The design is fairly straightforward: a preamplifier, then a two-tube transformerless splitter driving a push-pull output stage. She walks through the circuit a little, including the feedback path to the cathode of the first splitter tube. The power supply is a classic tube-rectifier design with a hefty low-pass filter built around a giant choke.

My favourite detail is the chassis. Instead of paying silly money for a purpose-made tube chassis, she used a pair of baking trays, and apparently they look surprisingly good. Most parts came from the junk box, including the output transformer, which is where the trouble started.

After a few mishaps and a bit of unintended oscillation, she ended up with an amp that shows promise but has noticeable distortion, which Hackaday puts down to that transformer. A better transformer should bring the figure into an acceptable range. There is a video of the whole build if you want the details.

I like this because it treats the amp as an electronics project first and a status object second. A reminder that the junk box plus patience can go a long way, and that high voltages deserve respect while you do it.

Source: Hackaday