I have build mine with an external heater supply from a DC-DC-converter...
Sorry to ask such a trivial question, but I do not have a lot experience on tracing curves from DHT. So here we go:
https://frank.pocnet.net/sheets/021/1/10.pdf
What you can see: The specs are given for AC-Heating with CT. The curves are given for D.C. heating....which results in different currents at the same neg. grid voltage. There is a comment that you have to substract 5V Vg when doing DC heating and looking at the curves, this is true:
- Va=250V, Vg=-23,5V, Ia=10mA when heated with AC (7.5V)
- Va=250, VG=-18,5V, Ia=10mA when heated DC for the curves.
I guess the question I have now is: Where do you measure ? Do you put your "cathode"-connection on the ground-side of the heater, on the positive-side or the CT done by some resistors ?
Example (all DC-Heating):
A. I do have here a Vt-62 coming NOS out of the box. If I measure with my utracer Va=345V, Vg=-20V, I get 33mA vs. the 25mA of the curves of the datasheet. That would be a great result ! (That is with two 5 Ohm-Resistors creating a CT and the "cathode" connection of the tester on them. )
B. If I connect the cathode-connection to the one heater end, I get 43,32mA, even better (..)
C. If I connect it to the other end of the heater I do get 24,17mA
So, I guess the question for me is: If I want to compare if a tube works at or above the curves published: What is the right measuring setup ? I saw Ron's recommendation to have a CT when measuring DHT, that is why I implemented it, but if I read the datasheet:
"...grid voltage should be referenced wo the negative end of the heater supply (when using DC)..."
I have my doubts that the CT gives the "right" curves (meaning those the industry publishes), but maybe I did not get it right...so, please enlighten me.
Sorry to ask such a trivial question, but I do not have a lot experience on tracing curves from DHT. So here we go:
https://frank.pocnet.net/sheets/021/1/10.pdf
What you can see: The specs are given for AC-Heating with CT. The curves are given for D.C. heating....which results in different currents at the same neg. grid voltage. There is a comment that you have to substract 5V Vg when doing DC heating and looking at the curves, this is true:
- Va=250V, Vg=-23,5V, Ia=10mA when heated with AC (7.5V)
- Va=250, VG=-18,5V, Ia=10mA when heated DC for the curves.
I guess the question I have now is: Where do you measure ? Do you put your "cathode"-connection on the ground-side of the heater, on the positive-side or the CT done by some resistors ?
Example (all DC-Heating):
A. I do have here a Vt-62 coming NOS out of the box. If I measure with my utracer Va=345V, Vg=-20V, I get 33mA vs. the 25mA of the curves of the datasheet. That would be a great result ! (That is with two 5 Ohm-Resistors creating a CT and the "cathode" connection of the tester on them. )
B. If I connect the cathode-connection to the one heater end, I get 43,32mA, even better (..)
C. If I connect it to the other end of the heater I do get 24,17mA
So, I guess the question for me is: If I want to compare if a tube works at or above the curves published: What is the right measuring setup ? I saw Ron's recommendation to have a CT when measuring DHT, that is why I implemented it, but if I read the datasheet:
"...grid voltage should be referenced wo the negative end of the heater supply (when using DC)..."
I have my doubts that the CT gives the "right" curves (meaning those the industry publishes), but maybe I did not get it right...so, please enlighten me.
RMS to DC converter
I did just that, except the implementation of a control loop. Instead, the output of the RMS to DC converter is readout by an analog panel meter. The AD737 is not really suitable for this task, as the maximum crest factor is only 5:1, while one needs at least 20:1. In this respect the LT1188 is more suitable, as the max. crest factor is 50:1. As far as I know, this is the only chip with such a high permissible crest factor. Regrettably, this beautiful chip is obsolete by now, but you can still buy it on ebay.
One may ask is it worth the time, money and effort to add RMS to DC converter to the uTrace? Yes, it is, as the real filament voltage is some 5% lower than specified in the menu. Especially in case of used tubes, this deviation has a noticeable impact on screen and anode currents.
Below you see the schematic, step responses and PCB. The Zener network at the right mimics a quadratic transfer function to compensate the quadratic voltage-temperature relation of the LT1188 (remember it's the power that defines the temperature). Without this network the step response is much slower (see 3rd pic, hor. scale = 1s/div).
For those who wants to build this converter, I've some spare PCB. You can get them for free, except postage (send me a PM).
Cheers, E.
I did just that, except the implementation of a control loop. Instead, the output of the RMS to DC converter is readout by an analog panel meter. The AD737 is not really suitable for this task, as the maximum crest factor is only 5:1, while one needs at least 20:1. In this respect the LT1188 is more suitable, as the max. crest factor is 50:1. As far as I know, this is the only chip with such a high permissible crest factor. Regrettably, this beautiful chip is obsolete by now, but you can still buy it on ebay.
One may ask is it worth the time, money and effort to add RMS to DC converter to the uTrace? Yes, it is, as the real filament voltage is some 5% lower than specified in the menu. Especially in case of used tubes, this deviation has a noticeable impact on screen and anode currents.
Below you see the schematic, step responses and PCB. The Zener network at the right mimics a quadratic transfer function to compensate the quadratic voltage-temperature relation of the LT1188 (remember it's the power that defines the temperature). Without this network the step response is much slower (see 3rd pic, hor. scale = 1s/div).
For those who wants to build this converter, I've some spare PCB. You can get them for free, except postage (send me a PM).
Cheers, E.
Attachments
And here you see my assembled version of the uTracer together with the RMS to DC converter. At the left: the panel meter for the heater voltage. The other meter reads out the screen respectively anode voltage.
The tube under test is a QQE06-40. Due to current limitations of the uTracer, only one half (at a time) is tested. The other half is cutoff by connecting the control grid to -40V. Disconnecting the anode instead, would be a bad idea, as the screen grid will be overheated. That's why I've made the -40V supply accessible.
The small black box next to SMPS, comprises the additional filter as recommended by Ronald Dekker.
Cheers, E.
The tube under test is a QQE06-40. Due to current limitations of the uTracer, only one half (at a time) is tested. The other half is cutoff by connecting the control grid to -40V. Disconnecting the anode instead, would be a bad idea, as the screen grid will be overheated. That's why I've made the -40V supply accessible.
The small black box next to SMPS, comprises the additional filter as recommended by Ronald Dekker.
Cheers, E.
Attachments
Last edited:
PSU filter
Hi Kevin,
On page #52 of the printed manual you can find it (see pic).
In addition, I've also put a capacitor of 1000uF before and one behind the inductor.
Whether it is really necessary and useful, I don't know, but as I had these components at hand, I added them anyhow (it doesn't hurt to try).
Cheers, E.
(PS: The PCB has been sent to you)
Hi Kevin,
On page #52 of the printed manual you can find it (see pic).
In addition, I've also put a capacitor of 1000uF before and one behind the inductor.
Whether it is really necessary and useful, I don't know, but as I had these components at hand, I added them anyhow (it doesn't hurt to try).
Thank you!
Cheers, E.
(PS: The PCB has been sent to you)
Attachments
Last edited:
I'd have to go back and have a look, that recommendation may actually have come after I built my 3. (Now 3+) I'm thinking along the lines of a common mode and differential mode choke, possibly combined. My switcher is a bit noisy.
Many thanks for the PCB, I purchased a LT1088 from a U.S. seller and will purchase the balance of parts once it gets here. I will use an external meter as I don't have real estate for an internal one.
Many thanks for the PCB, I purchased a LT1088 from a U.S. seller and will purchase the balance of parts once it gets here. I will use an external meter as I don't have real estate for an internal one.
I know that Analog brought out the AD8436 with much fanfare but it is still has a crest factor limitation relative to the LT1088.
Keysight recommends the thermal method for high crest factor signals -- I will never let go my HP3403C!
The beauty of the LT1088 is that it complies strictly with the definition of effective value: “the amount of AC power that produces the same heating effect as an equivalent DC power”.
For those who are interested in this chip: Also Klaus Albrecht (marshlake) has some 60 pieces still in stock (not just one!). You can order them here:
TRMS Wandler DC-100 MHz LT1088 | eBay
Cheers, E.
For those who are interested in this chip: Also Klaus Albrecht (marshlake) has some 60 pieces still in stock (not just one!). You can order them here:
TRMS Wandler DC-100 MHz LT1088 | eBay
Cheers, E.
I finally upgraded the HV on my uTracer to 400V -- I found it easier to remove parts and use the solder sucker to clean up the holes.
When calibrating I was having difficulty with "Vg" -- turns out that the 10nF cap was blown. It might be that the voltage off the buck-converter was too high for the device I used. Replaced it with a 100V Wima and all is well.
When calibrating I was having difficulty with "Vg" -- turns out that the 10nF cap was blown. It might be that the voltage off the buck-converter was too high for the device I used. Replaced it with a 100V Wima and all is well.
Ron Dekker just started a blog on the Utracer V6 -- if he gets it off the ground it should do 1kV and 1A. The uTracer V6
Hi All,
Probably it will be of interest to those who own the uTracer but also to those who would like to do a modeling of tube and trying different load lines. Some time ago I wrote a web-based software for the uTracer, which can control uTracer over Wifi using ESP32. My small hobby project went a bit further and I also wrote a javascript tool for analysis of the tube data acquired using the uTracer which can plot the load lines and also produce the Spice models. Ronald mentioned that tool in his blog in the "Lab Notebook". I host the tool at http://utracer.live and at the Roland's blog you can find some links to the screencast, but here are some screenshots. You can also upload you own data there and try to play with it. I hope it will be useful for some other people as well and I would also be happy to hear some suggestions.
Probably it will be of interest to those who own the uTracer but also to those who would like to do a modeling of tube and trying different load lines. Some time ago I wrote a web-based software for the uTracer, which can control uTracer over Wifi using ESP32. My small hobby project went a bit further and I also wrote a javascript tool for analysis of the tube data acquired using the uTracer which can plot the load lines and also produce the Spice models. Ronald mentioned that tool in his blog in the "Lab Notebook". I host the tool at http://utracer.live and at the Roland's blog you can find some links to the screencast, but here are some screenshots. You can also upload you own data there and try to play with it. I hope it will be useful for some other people as well and I would also be happy to hear some suggestions.
Attachments
Hi thumb,
The part that can drive and acquire the data from the uTracer require ESP32 module, so people who want to test that part have to buy that board somewhere (the price online is about $4-$6). For people who have that I can send the firmware and they can flash it to ESP32 and start using. I am still testing that part (mostly for handling all the exceptions and breaks in connection) but you can see how it works in this screencast:
Screen Capture on 2020-06-03 at 20-56-23.mov • Droplr
and here:
Screen Capture on 2020-06-03 at 22-04-46.mov • Droplr
But the part of the software that I put on http://utracer.live allows for uploading your own data acquired with uTracers's windows software and playing with loadlines and getting the models for (LT)Spice. You can see how it is done here:
Screen Capture on 2020-06-03 at 21-00-38.mov • Droplr
and here:
Screen Capture on 2020-06-03 at 21-08-26.mov • Droplr
The javascript webiterface now became more advanced and can do more than the acquisition of the data. I use it to build different loadlines. The analysis of the Harmonic Distortion is very accurate. I also use it to match tubes for push pull amps, because it is possible to load multiple files and compare upto 4 Ia/Is characteristics curves at the same time. There are actually several possible directions for extension, but I build it for myself and so far implemented the options that I use. It would interesting to hear some other suggestions.
The part that can drive and acquire the data from the uTracer require ESP32 module, so people who want to test that part have to buy that board somewhere (the price online is about $4-$6). For people who have that I can send the firmware and they can flash it to ESP32 and start using. I am still testing that part (mostly for handling all the exceptions and breaks in connection) but you can see how it works in this screencast:
Screen Capture on 2020-06-03 at 20-56-23.mov • Droplr
and here:
Screen Capture on 2020-06-03 at 22-04-46.mov • Droplr
But the part of the software that I put on http://utracer.live allows for uploading your own data acquired with uTracers's windows software and playing with loadlines and getting the models for (LT)Spice. You can see how it is done here:
Screen Capture on 2020-06-03 at 21-00-38.mov • Droplr
and here:
Screen Capture on 2020-06-03 at 21-08-26.mov • Droplr
The javascript webiterface now became more advanced and can do more than the acquisition of the data. I use it to build different loadlines. The analysis of the Harmonic Distortion is very accurate. I also use it to match tubes for push pull amps, because it is possible to load multiple files and compare upto 4 Ia/Is characteristics curves at the same time. There are actually several possible directions for extension, but I build it for myself and so far implemented the options that I use. It would interesting to hear some other suggestions.
I just wanted to make a small update for those who might be interested in the alternative web-based interface for uTracer 3, 3+ and 6, which works on all possible devices (laptops, tablets and phones) and all possible operating systems.
The webpage to try the functionality (with a bit outdated version) can be found here http://utracer.boffin.nl (this is instead of http://utracer.live which is now abandoned).
I just posted the latest release of firmware for 4MB and 16MB flash ESP32 modules, which is more stable and contains some new features (see the changelog for details). For example, there is a new type of Quicktest now, which just with a couple of measurements allows you to find the grid voltage that corresponds to the specified Va, Vs and Ia. One user suggested it (for matching tubes) and several already found it useful. The other features are for example restoring the last quicktest configuration after ESP32 reboot, drawing pinouts for user-defined tubes or easy generation of grid/anode voltage sequences for the "stepping variable".
One more useful feature that I forgot to mention, now during the quicktest, it is possible to choose automatic adjustment of Va and Vs (the option is also visible on the screenshot above, in the light-blue box). So when one sets Va and Vs, for example to 250V, the Ia will be reported for exactly those voltages, and there will be no typical voltage drop due to discharge of caps (which is about 5V for 40mA of Ia in my tests for my uTracer). Now uTracer will take one measurement extra to figure out the voltage drop and then readjust the applied voltages automatically.
The webpage to try the functionality (with a bit outdated version) can be found here http://utracer.boffin.nl (this is instead of http://utracer.live which is now abandoned).
I just posted the latest release of firmware for 4MB and 16MB flash ESP32 modules, which is more stable and contains some new features (see the changelog for details). For example, there is a new type of Quicktest now, which just with a couple of measurements allows you to find the grid voltage that corresponds to the specified Va, Vs and Ia. One user suggested it (for matching tubes) and several already found it useful. The other features are for example restoring the last quicktest configuration after ESP32 reboot, drawing pinouts for user-defined tubes or easy generation of grid/anode voltage sequences for the "stepping variable".
One more useful feature that I forgot to mention, now during the quicktest, it is possible to choose automatic adjustment of Va and Vs (the option is also visible on the screenshot above, in the light-blue box). So when one sets Va and Vs, for example to 250V, the Ia will be reported for exactly those voltages, and there will be no typical voltage drop due to discharge of caps (which is about 5V for 40mA of Ia in my tests for my uTracer). Now uTracer will take one measurement extra to figure out the voltage drop and then readjust the applied voltages automatically.
Attachments
Temperamental uTracer
I have an annoying issue with my uTracer where occaisionally it just does not want to play ball, and provides meaningless results, usually flat lines where the curve is not reproduced from the output voltagesand currennt of the tube under test.. Sometimes I can test again with a 100K calibraton resistor, and then the output looks fine. Sometimes it just works as expected.
Attached are two sets of curves for two 6AR5 tubes, where the intermittent issue kicked in for the second tube.
I am thinking there must be one of two issues:
1) It worked for a long time without an issue. The case I have is metal, and one time I noticed there was a spark when disconnecting the test leads. Dis I damage something on the board at that time, causing it to have an intermittent fault?
2) I have been very careful with using ferrite beads, but maybe have been overzealous! I have them on every pin and also from the 2mm jackplug socket too. The way they are wired 2 ferrite beads are in any circuit for any electrode - the one on the pin and the one on the jack plug socket. The beads are bypassed on unused sockets, but maybe they still contribute some inductance?
Any thoughts gratefully received!
I have an annoying issue with my uTracer where occaisionally it just does not want to play ball, and provides meaningless results, usually flat lines where the curve is not reproduced from the output voltagesand currennt of the tube under test.. Sometimes I can test again with a 100K calibraton resistor, and then the output looks fine. Sometimes it just works as expected.
Attached are two sets of curves for two 6AR5 tubes, where the intermittent issue kicked in for the second tube.
I am thinking there must be one of two issues:
1) It worked for a long time without an issue. The case I have is metal, and one time I noticed there was a spark when disconnecting the test leads. Dis I damage something on the board at that time, causing it to have an intermittent fault?
2) I have been very careful with using ferrite beads, but maybe have been overzealous! I have them on every pin and also from the 2mm jackplug socket too. The way they are wired 2 ferrite beads are in any circuit for any electrode - the one on the pin and the one on the jack plug socket. The beads are bypassed on unused sockets, but maybe they still contribute some inductance?
Any thoughts gratefully received!
Attachments
Worked for a long time. Now is intermittent.
I'd be thinking a poor connection "somewhere". I grant that your workmanship looks excellent, but Murphy's Law hides in dark corners and also right in front of your eyes. (That "VGA-like" connector is usually splendid, but can crap-out, especially if sparks happen.)
I'd be thinking a poor connection "somewhere". I grant that your workmanship looks excellent, but Murphy's Law hides in dark corners and also right in front of your eyes. (That "VGA-like" connector is usually splendid, but can crap-out, especially if sparks happen.)