A piece of equipment that I am very familiar with in my work is something which is called a “parameter analyzer.” Parameter analyzers are sophisticated pieces of equipment basically consisting of a number of programmable voltage / current sources and meters. They are used to measure the I-V characteristics of semiconductor devices, often down to pico-amp levels! Wouldn’t it just be great to have such an analyzer for tubes? Thinking about the construction of such a tube-analyzer, my enthusiasm quickly subsided. In a straightforward construction it means a number of heavy duty high voltage power supplies with associated transformers, cooling stuff, ventilators etc. Not really my cup of tea!
I have to admit that it was during a less inspiring moment of the lecture of the Christmas Service in our church in 2010 that the idea popped in my mind that it all could be done in a much simpler way when instead of a continuous measurement a pulsed measurement was used. The idea was so beautiful and simple! You take two simple boost converters, both of them only able to deliver small currents, and you let them charge two reservoir capacitors. Then during a millisecond or so you use the energy in these capacitors to bias the tube. When on top of that a micro controller is used to control the boost converters and to measure the currents, the final circuit could be unbelievably small and handsome!
Back from church the first experiments were quickly done. It turned out that a simple boost converter can easily charge a big 100 uF capacitor to 400 V. Needless to say that the remainder of the holidays was spent on working out the details of the circuit, the uTracer version 1 was born (on paper).
Breadboard testing of the version 1 and 2 uTracer
The version 1 uTracer never made it any further than a circuit diagram and a lot of experiments. Like the present version 3 it used a high voltage switch, but this switch had a lot of problems. In fact at a certain moment it failed, and in the blast that followed the charge of one of the 100 uF capacitor charged to 400 V destroyed every semiconductor on the PCB.
The disaster set me thinking about an alternative way to construct the tester. I realized that I could complete do without high voltage switches! Pulsing the grid bias from a negative value below the cut-off point to the set-point value, the tube itself could be used as a switch. A brilliant idea I thought at the time. This version was fully completed and is the version 2 uTracer. However, working with it I soon discovered a number of serious drawbacks. Diodes do not have a control grid, so that they couldn’t be tested. Furthermore, the way in which the current was measured – with a high side series resistor and DC blocking capacitor – inevitably resulted in an unacceptable drift in the measured currents.
An email with a circuit suggestion from Rene Schmitz from Germany set me on the trail of an alternative, and much more robust way to measure the currents; if several boundary conditions are satisfied, it is possible to “shift” the current sense resistors from the high-side position to a position in series with the cathode lead of the reservoir capacitor against ground. Away with drift and all the other problems with the current measurement, the version 3 uTracer was born! After finishing the version 2 uTracer, I made a wish list of features and improvements to be implemented in the next uTracer. I am happy and proud to say that all of these items have been implemented in the version 3 making it a valuable instrument.
In the course of the project I received many enthusiastic emails from people asking me if I could make a kit, or at least a PCB for the project. After much consideration I decided to do so. I have never sold anything I made for my hobby. Come to think of it, I never sold anything at all in my life, so it will be a completely new experience for me.
In the course of 2013/2014 a considerable amount of time was spent on something I called the uTracer4. The goal was a uTracer for (much) higher voltages, up to 1 kV or even higher. The circuit used pulsed transformers to boost pulses to the required voltages. Although elegant in principle the practical implementation of the circuit, was far from elegant. The main problem was that it was not possible to determine a priori the voltages of the measurement pulses because they depended on the currents drawn. This required iterative schemes which completely ruined the elegance of the whole concept. I really learned a lot about transformers and how they behave under pulsed conditions but finally I decided to abandon the project leaving the uTracer 4 uncompleted.
The problems with the uTracer 4 project set me thinking of what could be tinkered with the uTracer 3 to push it to somewhat higher voltages. A thorough investigation of the high-voltage switched made me convinced that 400 V operation was entirely feasible. This led to the uTracer 3+, basically a uTracer 3 with a number of modifications, mainly in the area of the high voltage switches. A simple conversion kit allows a uTracer 3 to be converted into a 400 V uTracer 3+.
Will there ever be a version 5 uTracer? I cannot help thinking YES! This was such a beautiful project that combined so many aspects of electronics that I think I became a bit addicted. What are the new features of a possible version 5? First of all higher voltages, up to 1 kV. Positive grid bias with grid current measurement is also high on my wish list. Another thing that has given me and many other people some headache is the PWM heater supply of the uTracer 3. A possible uTracer 5 will have a DC heater supply, possible in combination with current measurement. However, it may take some time before I start working on it; already for quite some time there have been a number of vintage radios waiting for some personal care, and that may take quite some time.
One last thing needs to be mentioned here. During the course of the version 2 development, in April 2011, my wife was taken seriously ill. It was critical and she spent nearly two months in hospital. It took several years before she was fully recovered. It has been the most terrible year in my life. During these difficult times the uTracer project helped me take my mind of things. It has been, and fortunately still is, invaluable to me!
During the Christmas 2012 holidays, a year after the uTracer project was started, the uTracer 3 was assembled and tested. Especially for this occasion I tidied up my workspace. This is such a rare event that I thought it worthwhile a (less successful) panorama photo.
A summary of the different uTracer hard- and software version
The hardware versions:
This version never made it further than some exploratory experiments.
The experiments are recorded in this Weblog (sections 1-7)
This version was completed into a working prototype. It used the grid of the tube to switch the anode current on and off and it used a rather curious construction with capacitors to measure the currents. It didn’t perform the way I wanted and the project was abandoned.
The experiments are recorded in this Weblog (starting from section 8)
The first commercial (300 V) version of the uTracer. The uTracer website is devoted to this version.
The experiments and development work leading to the uTracer 3 are recorded in this Weblog
The Graphical User Interface software controlling the uTracer 3 is GUI 3 (all subversions)
This version is almost identical to the uTracer 3 but has an extended high voltage range of 400 V. This version replaced the uTracer 3 in December 2014. A uTracer3 can easily be converted into a uTracer 3+. Instructions for this conversion can be found Here. There is a small conversion kit available with the necessary components.
The experiments and development work leading to the uTracer 3+ are recorded in this Weblog (sections 31 and 32)
The uTracer 3+ requires GUI version 3.11 or higher (see below)!
The idea of this version was to use transformers to generate measurement voltages in excess of 1 kV. The whole idea turned out to be more complex than originally planned so the project was abandoned.
The experiments for the uTracer 4 are recorded in this Weblog.
The software versions:
Both the uTracer3 as well as the uTracer3+ use firmware version 26C. The C, by the way, is the stands for “code protected”, meaning that the firmware cannot be copied.
The first Graphical User Interface release was version 3.6. The GUI is regularly updated; bugs are removed and new features are added. From time to time therefore new versions are released (e.g. versions 3.7 , 3.8 , … ). New full versions are available in the form of a complete installation package, as well as in the form of an exe only file, because after the GUI has been installed once, it is not necessary to go through the complete installation procedure again. Full GUI versions can be downloaded from the Download Page. A new GUI version is always announced by an email to the entire mailing list.
Prior to a new full release, I publish test versions of the upcoming new release. These “beta” versions have an extra index digit. So versions 3.12.1, 3.12.2, are (were) test/beta versions of the upcoming full release 3.12. Perhaps this is not so logical, but that’s the way it is. The test/beta versions can be downloaded here. These beta versions are always exe only downloads, so to run them you will need to have successfully installed a previous full release. A new beta version is usually not announced by an email, so check out the page regularly.
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