Vacuum Tube Pre-Amp Runs Entirely on Low Power Supply Voltage

Traditional vacuum tubes usually require 6.3V filaments and a high supply voltage to run properly. However, Albert van Dalen recently built a vacuum tube pre-amp that runs entirely on a lower supply voltage. The pre-amp runs on a 3.3V, inclusive filament voltage, and though the power supply isn’t very high, the tube amplifier still runs well, according to van Dalen.

Before getting to this stage, van Dalen purchased a cheap DIY 6J1 tube amplifier on AliExpress to conduct various experiments. Normally, the tube uses a supply voltage of 60V, but to see how much the power could be reduced, he gradually decreased the voltage going from 60V to 12V to 5V before reaching 3.3V. He achieved this in part by using a grid bias that resembles a bipolar transistor instead of a conventional single-ended design.

The results so far have been promising. Not only does the pre-amplifier work with a lower voltage, but it can also even be powered from a USB. For audio use, van Dalen says, “the gain is -3.5 and music sounds undistorted. Just the red light from the filament is dimmed.”

If you want to see van Dalen’s step-by-step process and try making one of these for yourself, check out his website. Looking forward to amp designs around this concept in the future.