uTracer... - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th January 2013, 07:11 AM   #1
nickds1 is offline nickds1  England
diyAudio Member
 
nickds1's Avatar
 
Join Date: Aug 2005
Default uTracer...

Some time ago I started to design a uP-based tube tracer, but, as normal, ran out of time - then in the middle of last year I found that Ronald Dekker, a Professor at TU/e & Philips Research was designing one. Ronald's site is at Ronald's electronic project site.

His device is called the uTracer - the project page is at The uTracer, a miniature Tube Curve Tracer / Tester.. This is a full-featured tester with a Windows-based front-end - the specifications can be found at uTracer specifications.

To cut a long story short, I bought myself the kit as a "me" Christmas present - took a day to build and test. The kit is of excellent quality - the design is very sound - e.g. short circuit & overload protected etc. - you would hope this was the case given the author's profession! The component quality was also very good and the supporting documentation very clear. Layout is good and the build process modular with continual testing. Its very professional.

Now been playing with the results for a few hours - very pleased indeed. All the PSUs (heater, anode & screen) are well-designed SMPS supplies and run cool - I've had the board running non-stop for several hours and it just gets slightly warm.

Whilst the electronics design is "open", the s/w is not - However, Ronald publishes the communications protocol between the PC app and the board should you want to write your own GUI. His rationale for not releasing the s/w source is that he doesn't want it to be ripped off by others - a fair comment in my book, especially when you consider the extraordinary amount of work he's put into designing this, and, for the benefit of all, fully documenting the process and design rationales in his blog - a really interesting read...

All running happily. Examples below of two plots - just playing to learn how to run different classes of tubes... to start with I chose a typical audio triode and pentode.

The attached photos show:
  • Setup screen for the 6CA7 tetrode test
  • On the test bench being intimidated:
  • Electro-Harmonix 6CA7 - Supressor connected to Cathode, 200V on screen, Grid stepped, Va varied and Ia plotted. 25W SOA is also shown. You can clearly see the "tetrode kink" on the graph
  • Svetlana 6C4C (aka 6B4G) - Here, I've overdriven a Russian 6C4C to check that the Iamax limit works (when I hit it the uTester give a "compliance error"). This graph has a 15W SOA curve and a 2.5K Ra load-line as well...
  • Completed controller board
Attached Images
File Type: png uTracer 3-6 with 6CA7 wired as a tetrode.png (68.3 KB, 1036 views)
File Type: jpg P1050387 (1).jpg (295.2 KB, 1005 views)
File Type: png 6ca7.png (15.8 KB, 977 views)
File Type: jpg 45.jpg (70.3 KB, 950 views)
File Type: jpg P1050385.jpg (316.9 KB, 962 views)
__________________
Nicko
"The whole plan hinged upon the natural curiosity of potatoes" - S. Lem

Last edited by nickds1; 4th January 2013 at 07:54 AM.
  Reply With Quote
Old 3rd February 2013, 08:08 PM   #2
jimmac is offline jimmac  United Kingdom
diyAudio Member
 
Join Date: Feb 2013
Location: Bury St Edmunds
Nicko, I agree. Just completed mine, construction was easy, instructions well done. Now I have to fine some tube sockets.
  Reply With Quote
Old 4th February 2013, 03:45 AM   #3
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I have one on the way, and will report once I get it and start to put it together..

I have also purchased a 19V 3A supply and a USB to TTL RS232 converter.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 11th March 2013, 12:35 AM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Here's mine. The kit went together without a hitch, the only hitch was when I ruined the top chassis plate by overzealous milling of the back surface of the top. Long story I don't want to relate, suffice it to say JB Weld works wonders but is ugly. This is a piece of test equipment so I will not be making it prettier.

Note that certain tubes with low voltage filaments need a little finagling to get the filament voltages right.

I found using my Keithley 2002 lab DVM that a setting of 2.8 - 2.9V delivered around 1.5 - 1.6V at the tube sockets with a 26 installed. (1.05A filament current)

For the 27 a setting of 3.7V was necessary to achieve 2.5V at the socket. (1.75A filament current) Note that technically the 27 filament current exceeds Ronald's current rating of 1.5A for the filament supply, but I've had no problems. I've fused the filament circuit at 2A.

Tubes with higher voltage, and/or lower current filaments will not have this issue. An external filament supply can always be used.

The voltage setting in the interface panel corresponds to a theoretical PWM duty cycle which when integrated in the filament corresponds to the value set, however the PWM based filament supply operates open loop so various losses conspire to require a higher than expected duty cycle at high load currents and low voltages. (The losses are due to finite on resistance in the mosfet, IR losses in the inductor, and attenuation of the pulses by the ferrites.)

Note on the Keithley 2002 and why direct measurements with many DVM may not work.. This meter has a true rms converter that is flat out to beyond 2.2MHz and can be AC coupled as well, most meters would probably struggle with the 19.5kHz square wave PWM waveform.
Attached Images
File Type: jpg 009.jpg (232.6 KB, 346 views)
File Type: png 26_dht_trace_panel.png (39.1 KB, 265 views)
File Type: png 26_dht_trace.png (8.8 KB, 190 views)
File Type: png 26 triode.png (7.6 KB, 153 views)
File Type: jpg utracer_26_tracing.jpg (178.2 KB, 315 views)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 11th March 2013, 02:32 AM   #5
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Nice!! Which file format options are available for storage of the measured data?

I've been wanting to build a tube tracer for a while, but have restricted myself from starting more projects until I've finished some of those I have going already. Assembling a board and having the software available would suit me just fine...

~Tom
__________________
Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 11th March 2013, 02:52 AM   #6
diyAudio Member
 
Join Date: Jul 2008
interesting board. any chance of interfacing it with something that when combined with this board would provide transconductance and amplification factor. As an example, one manufacters 6550 tube data shows 225V plate voltage, -14v Bias voltage and 12kGm. so we stick the tube in one of our gizomo's and while numbers can scroll in a predictable manner (i.e. as neg bias voltage decreases, bias current increases), we never can seem to be able to reproduce any manufacturers publish tube data in the area of Gm and amplification factor.
  Reply With Quote
Old 11th March 2013, 03:36 AM   #7
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Still learning what this thing can do, along with its various quirks. The GUI is coded in VB6 so for plots bmp is the only option, and data is saved in a format that is native to VB6, although I would need to check and see what it is. The program will calculate transconductance but I need to study the blog a bit more to figure out how to get it to do it..

Much more detail here: http://www.dos4ever.com/uTracer3/uTracer3.html
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 11th March 2013, 06:51 AM   #8
nickds1 is offline nickds1  England
diyAudio Member
 
nickds1's Avatar
 
Join Date: Aug 2005
If you are having problems with the inbuilt supply, you are perfectly free to use an external heater source...

The uTracer will plot dIa/dV (first differential of anode current vs. grid voltage for different anode voltages) and the reciprocal of that, i.e. transconductance and gm - you can have two Y axis active at any time.

This video explains how to do it:
uTracer 3, Measuring the Transconductance - YouTube

Note that Ronald has just issued free new FETs to replace the IRF840As in the kit as he's had problems with the recent ones he got from Vishay - the new ones are 07N60C3 - lower Qg & lower RDSon...
__________________
Nicko
"The whole plan hinged upon the natural curiosity of potatoes" - S. Lem

Last edited by nickds1; 11th March 2013 at 06:59 AM.
  Reply With Quote
Old 11th March 2013, 11:48 AM   #9
nickds1 is offline nickds1  England
diyAudio Member
 
nickds1's Avatar
 
Join Date: Aug 2005
Quote:
Originally Posted by kevinkr View Post
...The voltage setting in the interface panel corresponds to a theoretical PWM duty cycle which when integrated in the filament corresponds to the value set, however the PWM based filament supply operates open loop so various losses conspire to require a higher than expected duty cycle at high load currents and low voltages. (The losses are due to finite on resistance in the mosfet, IR losses in the inductor, and attenuation of the pulses by the ferrites.)
I was also interested in the open loop design - Ronald's comments centre around PWM calculations that should deliver the required power to the heater, however, as you correctly state, there are a host of DC losses in the system and no feedback - have you discussed this with him - I've found him very open to comments about the design... it wouldn't be rocket science to check the heater voltage at the heater once the warm-up has completed and to adjust the PWM if needed - you don't need the true RMS value, just the peak voltage at the heater and the delivered pulse width.

Quote:
Originally Posted by kevinkr View Post
Note on the Keithley 2002 and why direct measurements with many DVM may not work.. This meter has a true rms converter that is flat out to beyond 2.2MHz and can be AC coupled as well, most meters would probably struggle with the 19.5kHz square wave PWM waveform.
The reality of "True RMS" DMMs is an interesting one - many so-called true RMS DMMs are always AC coupled and/or ignore any DC component - I use a Tektronix DMM916 which can calculate correct RMS values (including any DC component) but its a grey area that a lot of test kit gets wrong...
__________________
Nicko
"The whole plan hinged upon the natural curiosity of potatoes" - S. Lem

Last edited by nickds1; 11th March 2013 at 12:05 PM.
  Reply With Quote
Old 11th March 2013, 04:46 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I do in fact talk to Ronald regularly, he is extremely knowledgeable and helpful, no one building this kit should be concerned about support - it's excellent. I'm amazed that he and his wife are able to provide all of the coverage they do. The kit is extremely well organized, and carefully packed, reminds me of the good old days of Heathkit.

The filament issue has been discussed and I will simply fine tune the filament voltage settings as required for the tube type I am going to measure. The system is very repeatable so I would not expect to need to make significant adjustments for any given type, but of course the measurements should be performed for any type that uses non-standard filament voltages, and I would recommend having a look if you are running tubes with high filament currents at any voltage. I'd like to avoid using an external filament supply in so far as that is possible.

Quite true that a true rms meter is not required for setting filament voltages accurately, I'm just lucky to have one that gives me accurate enough results. You can measure the peak amplitude value and pulse width vs period, calculate the duty cycle and multiply by the amplitude value to get the effective filament voltage across the tube.

The Keithley 2002 is a rather unusual meter which a former employer used as one of several choices for an internal calibration standard in a small semiconductor ATE test system. It is infinitely configurable and can do simultaneous AC and DC measurements and report the result in a number of ways. It's also insanely accurate and has a up to 11 digit display capability, it's by far the best and most expensive piece of test equipment I own.. (It's not been calibrated since I acquired it so its ultimate accuracy is currently unknown..)

I'm very pleased with my uTracer, not withstanding my chassis mishap, and heartily recommend it to anyone who wants to evaluate specific tube types for appropriateness for a given task. The curves tell a very easily understood story about the merit of any given type.

Repeatability incidentally is excellent. I've measured the same tube over a number of times and compared the results, they match extremely closely day to day. (I can't see any discernible differences in the curves I've taken.)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 08:12 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2