Arduino - Dual Channel Tube Amp Bias Meter Project

[ToneAlchemists]

Here's a great project for a two-channel tube amp bias meter using an Arduino! It's perfect for accurately biasing your tube amplifier.

Arduino Code for Dual-Channel Version: https://pastebin.com/YDUdLNTX
Parts:

• 1x Arduino Nano
• 4x Push buttons
• 1x SSH1106 Oled display board
• 1x ADS1115 ADC board
• 2x Bias Scout Probe kit

• Bias Scout Build Manual
• More info on the Video comments Section make sure to sort by newest comments

This dual-channel version is based on an original single-channel tube bias meter project:

Code for Original Single-Channel Version: Building a Tube Bias Meter - Arduino Code

and build blog

• 3D Print Designed - Bias Box for Single Channel Bias Meter

Feel free to share your updates or any other ideas! Cheers.

 

[shampeon]

I'm working on building an updated version of the dual bias meter, and adding some additional features (powering the unit from the heater pins, for example). I've updated the code to work on the latest version of the libraries, modified the source from .ino to .cpp, created a PlatformIo project for it, added support for SSD1306/1309 displays, updated the font, and added documentation. It's all on the GitHub repo:

GitHub - shampeon/DualBiasTester: A tube amp bias tester

A tube amp bias tester. Contribute to shampeon/DualBiasTester development by creating an account on GitHub.

github.com

I've got a couple open discussion topics right now for potential enhancements.

Right now I'm working on an enclosure for building it on an AirCookie prototype board, and am considering making a PCB in KiCad. I'm also working on a PCB for the probes that would fit a rectifier for powering it using 5VDC. I'll be sharing those files on GitHub when I'm done designing them.

 

[ToneAlchemists]

@shampeon I have to check it out, I've also updated the code as well over the past few months, also made a pcb board and updated the 3D printed enclosure for 3 buttons and screen (1.44/1.8 Inch SPI TFT LCD Full Color Display Module ST7789 OLED Screen) .. I've been using it the past few months with several of my tube amps ( Fender 30, Fender Prosonic (Head and Combo), Laney Aor Pro tube 50, Fender 68 Custom Pro Reverb). Latest update I did was to be able to set the Voltage Scale and Resistor for the 2 probes to be more accurate. here's the list of some the improvements I did below

Did some major updates added tube manager so you can add your own tube profiles. Here are some the major features I've implemented. about 98% code has been rewritten.

• Dual-Channel Measurement: Simultaneously measures and displays bias for two power tubes (A and B channels).
• Precision Hardware:
  • External Adafruit ADS1115 16-bit ADC for high-resolution readings.
  • Configurable gain and high sample rate (860 SPS).
  • Averaging of multiple samples (20 per reading) with noise threshold filtering.
• Display (1.8" ST7735 Color TFT):
  • Clear layout with tube name, target percentages (50%/60%/70%), voltage (V), current (mA), power (W), and dissipation percentage (%) for each tube.
  • Delta display (absolute current difference between tubes in mA).
  • Color-coded dissipation warnings:
    • White: Normal
    • Yellow: >70%
    • Red: >80%
    • Cyan: <50%
  • Efficient updates: Only redraws changed values to reduce any noticeable flicker.
  • Splash screen with "Bias Meter", creator credit, and version .
• Bias Calculations:
  • Plate voltage, plate current, power dissipation (W = V × mA / 1000).
  • Percentage of maximum plate dissipation.
  • Customizable screen-grid current subtraction (per-tube factor, e.g., 0.055 for 6L6GC, 0.13 for EL34).
  • "RAW" mode option (no screen compensation, 100W max).
• Tube Database Management:
  • Stores up to 10 custom tubes in EEPROM.
  • Each tube entry includes: name (up to 6 characters), max dissipation (W), screen-grid factor.
  • In-device tube manager: add, edit, or delete tubes without reprogramming.
  • Default tubes on first run (e.g., 6L6GC, EL34, 6V6).
  • Quick "RAW" mode access.
• Calibration Suite:
  • Per-channel voltage scaling factors (A/B).
  • Per-channel shunt resistor values (A/B).
  • User-adjustable over-voltage limit.
  • Live feedback during calibration (real-time calculated voltage/current).
  • Acceleration for faster adjustments when holding buttons.
  • Auto-save to EEPROM on completion.
• Safety Features:
  • Over-voltage detection with user-defined limit (default 600V).
  • Full-screen red "DANGER!" warning showing exceeded voltage and faulty probe (A or B).
  • Displays the offending voltage value.
  • Freezes operation with slow blinking until both channels drop 50V below limit.
  • EEPROM data validation and clamping (prevents crashes from corrupted data).
  • Save overflow protection.
• User Interface:
  • Three pushbuttons: Left/Right for navigation/adjustment, Center for selection/exit.
  • Main menu: tube selection, RAW mode, tube manager, calibration access.
  • Hidden calibration entry: hold left button during startup.
  • Robust input handling with debounce and hold detection.
  • Return to main menu from bias mode with center button press.
• Code & Reliability Optimizations:
  • Memory-efficient.
  • Persistent storage of all settings and tubes in EEPROM.
  • Safety-focused design for high-voltage amplifier work.

This version is a highly polished, user-friendly, and safe professional-grade bias meter suitable for guitar/bass amplifier technicians

I'll add some more photo's to see the UI

If you're interested in checking out my version I put it up on github.

 

[ToneAlchemists]

Hi everyone,

I wanted to share the final, version of this project. It has evolved significantly from the original concepts discussed earlier in this thread.

Project Name: Bias Meter (V11.4 Platinum) Repository: https://github.com/ToneAlchemy/BiasMeter

Key Features:

• Dual Probe Monitoring (Simultaneous).
• Tube Manager: Save/Edit/Delete tube profiles (EL34, 6L6, etc.) directly on the device.
• Safety Features: Over-voltage lockouts, input protection, and safety hysteresis.
• PCB Design: I have included KiCad files and Gerber files for a custom PCB that includes input protection diodes.

License & Safety:This project is now released under the GPLv3 License to ensure it remains open-source for the community.

• Attribution: This is an evolution of the excellent work by Kiel Lydestad and John Wagner (linked previously).
• IMPORTANT: This is a High Voltage project. It is provided "As Is" with NO WARRANTY and NO TECHNICAL SUPPORT. I cannot help with troubleshooting builds or modifying code. Please only build this if you are comfortable working safely with tube amplifier voltages.

Enjoy the build!

 

[TillMack]

That's fire ! Thanks for sharing this !