The uTracer is a small and affordable tube tester - or better a tube curve tracer - which measures all the important tube parameters and tube curves just the way as they can be found in data sheets. It is the ideal instrument if you want to design your own tube circuits, check the quality of a tube, or if you are simply a collector of tubes (like me) and you just want to bring those vintage wonders of technology back to life!

The circuit generates all the voltages needed to power up a tube under realistic conditions while it measures the currents. To keep the uTracer circuit as small as possible, all the user interface is taken care of by an elaborate Graphical User Interface (GUI) running under Windows. With the GUI it is possible to set-up a measurement, and to display and manipulate the measurement data so that it is represented in exactly the same sets of curves as in the datasheets.

The complete uTracer tube tester circuit measures only 10x16 cm.

The circuit is kept small through the use of state of the art technology and circuit concepts. By using a pulsed measurement principle, “heavy” and expensive transformers, heat-sinks and fans are eliminated, making the uTracer one of the cheapest, but also one of the smallest tube testers / tube curve-tracers around. On top of that, the pulsed measurement allows for testing of tubes in A2 (positive grid) mode and at power levels far beyond their “safe operating area.”

The control panel of the uTracer, the Graphical User Interface (GUI). In this figure the Ia/Is-Va curves were measured for an EL84 (6BQ5)

The complete uTracer consists of four components:

  1. The Graphical User Interface (GUI), an intuitive and flexible program running under windows. It is used to start a measurement and to display or store the measurement data. Additionally Nick Barton has written an alternative GUI which was also ported to Linux.
  2. The uTracer hardware, a 10x16 cm PCB containing all the electronics, boost converters and a programmed PIC microcontroller which controls everyting and communicated with the PC. The hardware is available as a complete kit, or as a programmed and tested PIC processor only.
  3. A power supply chord. The whole uTracer is powered by a an old 19.5 V laptop power supply chord. These chords easily can supply the power to drive even relatively “heavy” popular output tube like the EL34, and on top of that are cheap while most people have an old one lying around. The power cord is not a part of the kit.
  4. A tube socket array. Most users of the uTracer will have their own ideas and preferences for the mechanical construction of their tube tester: which sockets to use, what casing, rotary electrode switches or something more simple …. For this reason, the tube socket array is not included in the kit.

This project started nearly two years ago, and has grown into an extensive project. The “project-blogs” on my site generated a lot of response and enthusiasm from all over the world. Many readers have asked me to make a kit out of this project. After a lot of consideration I decided to do so, so here it is: the uTracer V3 kit for sale!

Starting from January 2015 the uTracer3+ will replace the original uTracer3. The uTracer3+ is identical to the original version but with an extended voltage range of 0 to 400V!

These pages give you a quick overview of the uTracer, how it works and what it is capable of, and how you can build one yourself! If you want to know about the history of the project have a look at the uTracer V3 project-blog.

Apart from the full curves it is also possible to quickly measure the most important tube parameters in a specific bias point.
In this example an ECC82 (12AU7) and EL84 (6BQ5) are tested in their nominal bias points.
For double triodes both sections are measured simultaneously.

The curves measured with the uTracer can be saved and manipulated in several ways.
This example shows how the harmonic distortion components are calculated from a given load resistance, bias point and supply voltage for an EL84.

The series of videos below give an impression of how the uTracer operates. The videos are a bit outdated because they show an old version of the GUI, while in the newest version many new features have been added. The basic operation and layout of the GUI has however remained the same.

Measurement Setup
Graphical Output

Click on one of the images for a guided tour through the new GUI!

Extensions available for the uTracer!

As it turns out the uTracer is an ideal platform for further experimenting! Over the time I have investigated and published several extensions that either extend the measurement range of the uTracer basic circuit, or that make it useful for other applications. Most of these extensions only require a small additional circuit that can easily be built on a piece of perfboard which can be added to your uTracer hardware. You can find most of these extensions on my “Lab Notebook” page, but for convenience I have listed them here:

Higher anode and screen currents Click Here
With only a few components modified and a new release of the GUI you can increase the current range for the anode and screen channels to up to 1A!
The circuit requires GUI version 3.12.6 or higher (Click Here)

More accurate low and even positive (!) grid voltages! Click Here
A small add-on circuit that allows you to accurately generate low grid voltages. In contrast to the standard grid voltage circuit of the uTracer, this circuit can deliver currents which improves the accuracy around 0V.
Additionally the circuit is able to generate positive grid voltages.
The circuit requires GUI version 3.12.3 or higher (Click Here)

Measure gird currents for positive grid biases! Click Here
A slightly more elaborate circuit compared to the previous one not only allows you to apply positive grid biases, but also to measure the resultant grid current.
The circuit requires GUI version 3.12.3 or higher (Click Here)

Test and re-form vintage electrolythic capacitors with your uTracer! Click Here
With a few resistors and diodes you can turn your uTracer into a useful device to test and re-form the electrolytic capacitors from your vintage equipment. In many old capacitors it can restore the thin dielectic bringing them back to life again.
The circuit requires GUI version 3.12.5 or higher (Click Here)

Use your uTracer to measure the characteristics of transistors! Click Here
With a handful of resistors and a rotary switch you can use your uTracer to trace the curves of NMOS and NPN (high-voltage) transistors.
Runs with all GUI versions.

Run the quick test via Bluetooth from your Android app! Click Here
This contribution from the son of a uTracer owner allows you to run the quicktest from an app on your Android tablet or phone. The contribution also describes how you can connect your uTracer with a blue tooth connection.

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