The Project: Tone Alchemy – Bias Meter (V11.4 Platinum)

I designed the ToneAlchemy Bias Meter to solve a common problem facing guitar amp technicians and hobbyists: commercial bias probes are often expensive, limited in functionality, or difficult to read.

This project is a professional-grade, open-source Arduino tool that allows for the precise measurement and setting of bias for power tubes (EL34, 6L6GC, 6V6, KT88, etc.) using a high-resolution color interface. Unlike simple multimeters, this tool calculates Plate Dissipation (Wattage) in real-time, ensuring your amplifier runs at its optimal operating point safely and accurately.

Why Build This?

Commercial tools often give you a single number without context. The ToneAlchemy Bias Meter (V11.4) was engineered to provide Lab-Grade Accuracy and Safety features not found in typical DIY builds.

Key Features (11.4 Platinum)

  • Dual Channel Monitoring: View real-time statistics for both Tube A and Tube B simultaneously on a crisp OLED display.

  • True Plate Dissipation: Standard probes often give inflated readings because they measure total cathode current. This meter uses Screen Current Correction math to subtract the screen current (Ig2), displaying the actual Plate Dissipation wattage for higher precision.

  • Tube Manager Database: Save and recall settings for up to 6 different tube types. You can define specific Max Dissipation limits and Screen Factors for EL34s, 6L6s, and more.

  • High-Precision Hardware: Utilizes an ADS1115 16-Bit ADC for superior resolution compared to standard Arduino inputs.

  • Enhanced Reliability: Features a Watchdog Timer (WTD) that automatically resets the device if tube amp EMI (electromagnetic interference) causes the display to freeze—critical for working on live amps.

  • Software Calibration: No manual trimpots required. You can calibrate the Shunt Resistors and Voltage Scalers directly through the on-screen menu.

  •  Warning: Tube amps contain lethal voltage. Build at your own risk.

Open Source & DIY

This project is fully open-source (GPLv3). I have provided everything you need to build your own:

  • Firmware Source Code: (Arduino .ino)

  • 3D Printed Enclosure Files: (.STL)

  • Custom PCB Design: (KiCad/Gerber files)

  • Bill of Materials: Full parts list.

DOWNLOAD ON GITHUB

⚠️ SAFETY WARNINGS: High Voltage   

Tube amplifiers contain lethal high voltage (often 400V–500V+), even when powered off and unplugged.

This project involves building and using test equipment that interfaces directly with these dangerous circuits.

  • Risk of Death: Incorrect wiring of the bias probes or misuse of this device can expose you to lethal current.

  • Qualified Personnel Only: If you are not trained in high-voltage safety or are uncomfortable working with live circuits, do not build or use this device.

  • Disclaimer: This project is provided “as is” with no warranty. The author assumes no liability for injury, death, or equipment damage. Use entirely at your own risk.

BiAS METER CREDITS & LICENCING INFO