Summary of VACUUM TUBE PRE-AMPLIFIER RUNS ENTIRELY ON 3.3V, INCLUSIVE OF FILAMENT VOLTAGE
Albert van Dalen designed a vacuum-tube preamplifier that operates entirely from a 3.3V supply including filament voltage. Starting from a 60V 6J1 DIY amplifier, he progressively reduced supply voltage to 12V, 5V, and finally 3.3V by using a grid bias resembling a bipolar-transistor arrangement rather than a conventional single-ended bias. The USB-powerable preamp delivers usable tube sound with a gain of −3.5 and low distortion; the filament glows dimly. Odd behaviors at 3.3V include a positive grid-to-cathode voltage and a relatively high grid current of 0.3 mA.
Parts used in the 3.3V Vacuum Tube Pre-amplifier:
- 6J1 vacuum tube (from a cheap DIY 6J1 tube amplifier)
- Power supply capable of 3.3V (USB power)
- Filament/heater integrated with the 6J1 tube (powered at 3.3V)
- Grid bias network arranged like a bipolar transistor
- Passive components for biasing and coupling (resistors, capacitors)
- LED filament indicator (red light)
- Amplifier chassis or PCB from the DIY kit
- Input/output audio coupling connectors
Most vacuum tubes need about 6.3V high supply plus filament voltage to operate. Running at 3.3V inclusively of the filament voltage, the new vacuum tube amplifier from Albert van Dalen has proven it possible to have one with the capacity to operate on an entirely low power supply voltage and still work well.
To be able to do experiments with vacuum tubes, I bought a cheap DIY 6J1 tube amplifier on Ali Express. Like most vacuum tube circuits, it uses a relatively high supply voltage of 60V. However, a high voltage is not always required for vacuum tubes, sometimes 12V is used. I was curious how far one can go with reducing the power supply. Nowadays the most common used power supply voltage for electronics is 3.3V and before this was 5V.” says van Dalen as he explains how he started with his design and was able to gradually decrease the voltage going from 60 V to 12 V to 5 V and then finally down to 3.3V partly by using a grid bias that looks like a bipolar transistor instead of the usual single-ended design.
Van Dalen also added that asides being able to work with a low supply voltage, power the preamp can also be used for audio purposes and can easily be powered from a USB.
Tube amplifiers are used for nostalgia reasons and to get the characteristic tube sound. For this purpose, this preamp is useful, and you can simply power it from USB. The gain is -3.5 and music sounds undistorted. Just the red light from the filament is dimmed.
However, some of the oddities caused by this very low supply voltage as observed by van Dalen in his experiment included a positive grid-cathode voltage instead of being negative and a very high grid current of 0.3 mA.
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- Can a vacuum tube preamplifier run entirely on 3.3V including the filament voltage?
Yes, Albert van Dalen demonstrated a preamp that runs entirely on 3.3V including the filament voltage. - What tube was used in the 3.3V preamplifier experiment?
The experiment used a 6J1 vacuum tube from a cheap DIY 6J1 tube amplifier. - How was the supply voltage reduced from typical high voltage to 3.3V?
Van Dalen gradually decreased the supply from 60V to 12V to 5V and then to 3.3V, partly by using a grid bias that resembles a bipolar transistor instead of a usual single-ended design. - Can the preamp be powered from USB?
Yes, the preamp can easily be powered from USB. - What is the audio performance of the 3.3V preamp?
The preamp yields a gain of −3.5 and music sounds undistorted, with the filament red light dimmed. - Are there any unusual operating characteristics at 3.3V?
Yes, unusual observations include a positive grid-to-cathode voltage and a relatively high grid current of 0.3 mA. - Why build a tube preamplifier that runs on low voltage?
It allows achieving tube characteristic sound and nostalgia while enabling low-voltage power sources like USB. - Does the filament still glow at 3.3V?
Yes, the filament glows but the red light is dimmed at 3.3V.
