After the success of the Neutrino project, it was natural to go further, so Baryon Omega was born, a completely new tube audio processor based on the VT-33 tube connected as a triode. A real project, tested and ready to be replicated by anyone looking for true tube sound in a modern system, but without the compromises of unnecessary preamplifiers and buffers.
The choice of the VT-33
The VT-33 is a small directly heated tube originally designed for battery powered applications. Its commercial name is Type 33, and it was classified as an audio output pentode by the United States government (VT = Vacuum Tube). Under standard conditions, when connected as a single ended class A pentode, it delivers about 700 mW. In this project, however, it is used in triode configuration, where it gives its best in terms of naturalness and harmonic content.
This tube has a very interesting feature for the modern DIY builder, it only requires 2 V at 260 mA for the filament. This makes it very easy to power with stabilized DC, without the need for large heatsinks or complicated regulators.
Triode connection and impedances
Once connected as a triode, the VT-33 shows an internal resistance of about 2100 ohm. Working on a load line of 8500 ohm, very controlled and pleasant distortion is obtained, with a characteristic harmonic profile dominated by the second harmonic and a barely perceptible third.
I specifically designed two output transformers model i8K5-820 – Type33, each with:
- 8500 ohm primary
- 820 ohm secondary
The 820 ohm impedance is not accidental, it is the value that allows obtaining at the output a voltage very similar to the one applied to the VT-33 grid, thus making it possible to benefit from the full tube effect without altering the system gain, as explained in the dedicated article about tube audio processors.
Constant current filament supply
To respect the delicate VT-33 filaments and maximize their lifespan, the power supply was designed for constant current. I built a dedicated pair of inductors, model 25i18 rated at 300 mH and 300 mA maximum current, used in a circuit that employs an LM317 configured as a 260 mA constant current regulator.
After the regulator there is a CLC filter that removes any trace of residual noise generated by the LM317. The oscilloscope photos speak for themselves, extremely low noise, natural soft start and no mechanical stress on the filament during power up.
A real, complete and available project
The Baryon Omega is not a theoretical project or a paper prototype, it has been actually built and tested on a workbench, with real and measurable results. In the photo below you can see the complete set that you receive when purchasing the Premium KIT, including the detailed electrical schematic and the custom designed transformers (tubes not included).
Frequency response graph
Harmonic spectra of the tested sample
If you are interested in building a custom Tube Audio Processor, or if you want to purchase the complete transformer set with the premium schematic, contact me directly, we can also adapt the project to other compatible tubes, as long as they have Ri values compatible with the design of a serious interstage transformer. True tube sound is not improvised, it is designed, built and listened to.