Comments for page: uTracer-HR You Can Build

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Posted by Markus January 19, 2021 - 02:53 pm
Hi Steve, do you think I will also need a heatsink if I mainly test 12AX7 tubes and only up and then a EL34 (1.5A) or 6L6 (0.9A)? Regards, Markus

Posted by Steve L. January 19, 2021 - 10:32 am
Hi Markus, You're very observant! The heatsink was a late addition and didn't make it into most of the pictures. Of course, it is shown in the HRB construction section of Part III. It's also slightly visible in slide 28 of the gallery in Part III. Thank you for bringing this to light. I do recommend using the heatsink as the XL4005 chip can get quite hot when maximal heater power is being delivered. That heating is what limits the HRB to a continuous 2 or 3 amps, versus the 5 amps or so which it can deliver for short periods at 6.3V.

Posted by Markus January 19, 2021 - 02:19 am
Hi Steve,
one more question: in your instructions on how to build the heater supply you indicate that a heat sink has to be mounted to the XL4005 while there is no heat sink in the images of your completed ĶTracer. Does the XL4005 require heatsinking? Regards,
Markus

Posted by Markus January 12, 2021 - 01:14 am
Thanks for your explanation, Steve! I totally forgot about your sense lines.

Posted by Steve L. January 11, 2021 - 02:39 pm
Thanks, Markus. The 2-pole DC-type jacks were needed to support a second channel, required by the remote sensing feature of the heater regulator board. That eliminates the voltage drops in the heater and ground connections. Quoting from Appendix B:

"A highly accurate heater voltage source would be of little value if nothing were done about voltage drops in the heater and ground connections. With the connectors and wires, itís pretty easy to find 0.1Ω; or more. At 3A, that drops 0.3V or about 5% of 6.3V, which is way too much error from that one contributor.

Hence, I decided that remote sensing for the heater supply is necessary. With remote sensing, the regulator sets the voltage at the socket, rather than at the regulatorís own output. It does that by using separate wires to bring back the voltages at the two heater pins. Very little current flows in these sense lines, insuring that the regulator is seeing what is actually at the socket pins. Notice, however, that this implies that two separate lines must be connected to each pin: drive and sense. That requires two-pole connectors."

By the way, for convenience in connecting lab equipment to the tube, the red banana jacks are also provided for each pin. Those also use the sense lines, making it easy to measure the tube's pin voltages without error from voltage drops.

Posted by Markus January 11, 2021 - 02:01 pm
Cool report!
Why did you use DC-type jacks for the tube pins and the voltage sources and not banana jacks?
Regards,
Markus

Posted by Steve L. September 16, 2020 - 06:57 am
Hi Hoby, Thank you for your kind message. I'm not sure what you mean by, "I need bin hex files" but I will be happy to help if you have further questions. If you are looking for files such as schematics and panel art for this project, the download links are at the end of Part II of this article. Best wishes for your project.

Posted by hoby September 16, 2020 - 06:17 am
Congratulations on successful article work. I will do it as a hobby. I need bin hex files. thank you. elektordu@gmail.com

Posted by Steve L. March 24, 2020 - 11:05 am
jgxbos (Juan) had also posted his question below in the Google groups uTracer forum and I followed up by posting my 3/22/20 reply from below, there as well. In his kind thank-you note there, he also mentioned that he wanted to modify the heater regulator circuit for other and variable voltages. Here are a few thoughts on that. (I didn't put this there because the thread was about something else.)

Thoughts about modifying the heater regulator board (HRB) for other and variable voltages:
(Please refer to the HRB schematic.)
  • The Loop Integrator compares the feedback from the voltage dividers to a 2.5V reference and steers the output to make the feedback voltage become 2.5V.
  • Adding a 2.5V output setting is easy because no divider at all is needed---we want the output steered directly to the reference voltage; no adjustment needed. However, the Loop Integrator depends on the source resistance of the feedback being about 20Kohms. So instead of directly connecting the Heater Sense (HtrSen) line directly to pin-3 of IC201, we need to insert a 20K 5% resistor. Caveat: Loop stability has not been tested in this condition.
  • Note that the lowest possible HRB output voltage is 2.5V in this circuit.
  • To get variable output, you can add another divider (or replace an existing one) as shown in this schematic: http://www.tronola.com/misc/uT_Heater_Reg_Var_output_example_1800.gif
    Please bear in mind that this is a brief effort and should be considered experimental. In this concept, I added the Fixed/Variable Select switch which lets you choose the (front panel) 2.5-15V Adjust pot, R215. The 15V max is approximate and can be increased modestly by decreasing R217. The max must be well under 19V though. I hope this is what you had in mind but if not, please let me know. Questions and comments are welcome

Posted by Steve L. March 22, 2020 - 07:20 pm
Hi jgxbos, The value of R211 should be 2.7K. Sorry that the Mouser part number in the BOM is incorrect and should be CF1/4C272J. I will correct that shortly. In case you don't have a 2.7K 1/4W resistor, I will be happy to mail one to you, assuming it's in the U.S. You can email me the mailing address. My email is found by clicking the About button on the Tronola Home page. By the way, you are correct that the photo shows the multiplier color differently---there was later work on improving loop stability and the photo was taken before that. Sharp eyes! I will try to correct the photo as well.

C207 is discussed in Part III of the article. (You can search for "C207".) It is important because C207 improves stability. It should be soldered on the bottom of the heater regulator board as shown in Slide-25 of the Gallery linked from that same page.

Thank you for reporting the BOM error! I will be happy to help if you have any other questions or problems.


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