Tube Theremin Design Mods

Kendrick Sellen's Tube Theremin Design Mods represent a thoughtful and practical approach to building a classic vacuum tube theremin. Drawing on the rich history of tube-based circuits from the 1940s and 1950s, Kendrick has developed modifications that improve stability, playability, and tonal quality.

The theremin is one of the few electronic instruments that still commands respect for its vacuum tube heritage. Many players and builders prefer tube designs for their warmth, harmonic richness, and the unique character they bring to the instrument. Kendrick's modifications build on this tradition, offering a modern take on a classic circuit.

The Design Philosophy

Kendrick's approach to tube theremin design focuses on several key areas:

• Stability: The circuit is designed to minimize frequency drift, a common issue with older tube designs. Improved power supply regulation and careful component selection ensure consistent performance.
• Playability: The pitch and volume response curves are optimized for smooth, natural playing. The modifications make it easier to achieve accurate intonation and expressive dynamics.
• Tonal Quality: The tube circuitry provides a warm, rich tone that many theremin players prefer. The modifications include adjustable equalization to shape the sound to your taste.
• Reliability: Using readily available components and modern manufacturing techniques, these designs are built to last.

Building the Tube Theremin

Building a tube theremin is a rewarding project for anyone with basic electronics experience. The circuit uses vacuum tubes that are readily available and relatively inexpensive. Key components include:

• Vacuum tubes: Typically 12AX7, 12AU7, or similar dual triodes.
• Coils: Miller #9001 or similar adjustable inductors for the oscillator circuits.
• Capacitors and resistors: High-quality components for stability and low noise.
• Power supply: A well-regulated supply to ensure stable operation.
• Antennas: Flat aluminum plates or rods for pitch and volume control.

The modifications developed by Kendrick Sellen are documented in detail, with schematics and parts lists available through TECI. These designs have been built and tested by many enthusiasts, and the results have been consistently positive.

The Moog Connection

The photographs on this page include images of a Moog tube theremin from the 1950s. Bob Moog began his career building theremins, and his early designs were based on vacuum tube circuits. These instruments are highly sought after today, and they represent an important part of theremin history.

Kendrick's modifications draw on this tradition, combining the classic Moog design with modern improvements. The result is an instrument that honors the past while offering the performance and reliability that today's players expect.

Getting Started

If you are interested in building a tube theremin, here are some steps to get started:

• Study the schematics: Familiarize yourself with the circuit design and understand how each section works.
• Source components: Gather the tubes, coils, capacitors, resistors, and other parts you will need.
• Build the power supply: Start with the power supply section, as it is critical for stable operation.
• Construct the oscillators: Build the pitch and volume oscillators carefully, paying attention to component placement.
• Test and tune: Once the circuit is built, test each section and calibrate the instrument for optimal performance.

For more detailed information, including schematics and parts lists, contact TECI through our contact page. We are always happy to help fellow enthusiasts with their projects.