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MiniTubeAmp
A Power Transformer-less Tube Amplifier Design That Fits In Your Bag!

Overview
After building my first tube amp from a kit, I decided to embark on a bit of an adventure. Tube amps seem to be a very "experiment and listen for yourself" field, with everyone giving their own advice on what sounds the best. I gave myself the challenge of making a low-cost, miniature tube amp for experimentation and utility: this is the amp I will be testing the Chip Maestro with! Over the years, I have been using this charming little amp to test the Chip Maestro. I found it in a guitar store when I stopped in to pick up some new strings. It was sitting in the As-Is box, and the owner let it go for a measly 5 bucks. It did not turn on at all, so I ripped the guts out and stuffed a CMOY amp inside. This became the perfect Chip Maestro amp, as it was portable and quite loud for its small size. It could easily fill a small room, maybe even a living room. With my recent experiments into tube amps, I decided to give this retro styled exterior a retro interior as well. After eliminating regular vacuum tubes from the plans as they were too hot and bulky, I found some documentation on amps built from subminiature tubes. Not a lot of research went into these, as during their time they were reserved for military use, and soon after replaced by transistors. I found a few sites where there were a few schematics available, and used these two to begin designing:http://thejaffes.org/sites/all/files/miniamp.pdf &http://www.harmonicappliances.com/powerman/powerman.html One difficulty with keeping tube amps small is the power transformer. Usually a massive beast of iron and copper, this is what is responsible for generating the 100+ Volts necessary to shake electrons loose. Larger tube amps typically suck down lots of current too, so all this raw material and engineering is not cheap. Therefore, another plus of submini vacuum tubes is that they sip power, about 6.5mA each! Using modern SMPS tech, I repurposed one of the boost converters from a nixie tube project to output 135VDC into these tubes. Using an SMPS also means I can do away with most of the bulky smoothing capacitors, as the frequency of the switching is well above listening frequency (at least to my ears, I can not hear any whine from the SMPS). Over the course of two evenings, I worked on stuffing everything into this casing. As the tubes get quite warm, I will have to devise a solution for keeping them from melting the plastic casing. I will likely redo the project on breadboard and optimize the parts before I commit the final project to the case, completely enclosed. However, that will have to wait until I finish the Chip Maestro! Lastly, how does it sound? Well, I can definitely hear the "warmth" many tube aficionados go on about, but this design will definitely need some tweaking to reduce a few hums and noises that crop up.
Pictures
Files
Schematic: MiniTubeAmpSchematic.png

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Welcome to my online build logs. All these projects are open-source and free to use for non-commercial purposes. Reach out to me at jarek-at-soniktech[dot]com if you have any questions!

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