External filament power supply

[Allan Smith]

Hi all,

I am building uTracer 3+, and will also build an external filament power supply, as designed by Stephen Lafferty. 

I want to hear if there is someone who have an extra print PCB, Heater regulator board, they will sell / send to me in Denmark.

Thanks in advance and Best Regards

Allan Smith

[Allan Smith]

I am building uTracer 3+, and will be building external filament power supply, as designed by Stephen Lafferty. Want to hear if there is one of you who has an extra print PCB, Heater regulator board, they will sell / send to me in Denmark

[jgx plato]

Hello Allan:

Sorry, but I built my power supply for the utracer with a pcb that provide me a guy in the forum, but I guest that they sell all the pcb a. 

Maybe you can order some pcb from China using the layout in the forum, I don’t know...

Any doubt, don’t hesitate ask me

Regards

Juan 

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[Bill van Dijk]

There is no “magic” involving an external power supply, so there are a lot of options. If you want something nice, but affordable, do have a look on e-bay. Do a search for “adjustable power supply”, and you will see a lot of nice units with meters etc. built in. Myself, I built a power supply using a transformer from my ‘spare parts supply’, and a small DC buck step down board, again from e-bay. Remove the on-board adjusting pot, and replace with a 25-turn precision pot for fine control and add one of the V/A meter units. It is cheap, and works great! Lots of options depending on how much money, or how much work you are willing to put into it.

 

Cheers, Bill

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[jgx plato]

Totally agree!

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[Charles Deryl]

Hello everybody :

A 230 to 19,5V/1,3A  power supplie for a ridiculous prise : https://www.banggood.com/fr/Universal-AC-Adapter-Charger-Power-Supply-Adapter-19V-1_3A-For-LG-ADS-25FSG-19-ADS-40FSG-19-TV-p-1403566.html?rmmds=myorder&cur_warehouse=CN

And then, an external buck-boost power supplie up to 36V and 5A for a crazy price, dont bother :  https://www.banggood.com/fr/XYS3580-DC-DC-Buck-Boost-Converter-CC-CV-0_6-36V-5A-Power-Module-Adjustable-Regulated-Laboratory-Power-Supply-Variable-p-1601308.html?rmmds=myorder&cur_warehouse=CZ

Charles

[shlafferty]

I think it's marvelous that folks have proposed such low-cost solutions to providing an external heater supply for the uTracer. The original poster mentioned the solution I presented in the article, http://www.tronola.com/html/tube_analyzer_you_can_build_page1.html, which would add about 27% to the cost of a basic uTracer build, so the question is: What would justify the extra cost? Some might cite the eye-popping accuracy figure but the main advantage of the Tronola heater regulator board (HRB) lies in its remote sensing feature. That technique lets the HRB set the voltage actually at the tube socket, as opposed to the voltage at the output of the regulator itself.

You might think that there wouldn't be much difference but the article gives an example in which 0.1V is lost between the heater supply and the socket. With the similar loss on the ground side, this results in 4% error. I've found that such errors are hardly unusual. With a 5U4, it's only 0.033 ohms on a side. Errors in the uTracer measurements themselves can be in the 2-5% range, so the result could be 9% off. Heater voltage directly impacts tube performance

Now consider the case of testing power tubes. One tube expert recommends rating a tube as good if it achieves 80% power output, else, it's weak or bad. So if the tube is allowed to lose only 20% of its ideal power to reach end of life, it seems clear that test equipment that can be 9% off isn't okay. Remote sensing can alleviate this issue. An added benefit is that it takes care of any variations in connector resistance, so there's no need to worry about whether the plug is as tight as it should be or whether things might change with moving the connectors around.

Nevertheless, this is hardly the only solution. You can get just as good results with a manually adjusted heater supply, as long as you measure heater voltage directly at the tube socket after the tube is warm. If the only thing which my article has done is encourage folks to provide an accurate heater supply for the uTracer, I will consider it to be a success. Once again, kudos to those who have found economical ways to do this.

Steve L.

[Bill van Dijk]

With all due respect, I do appreciate what you are saying. But….

 

This all assumes that the tube specifications are absolutes, which they are not by far. Manufacturing tolerances vary widely, and is recognized in the data sheets right up front. Where the filament specifications are given, you will often see a minimum and a maximum or a tolerance. For a typical 6.3V filament it is usually something like +- 0.6V. That means the manufacturer says the tube will perform as stated with a filament voltage of 5.7 to 6.9 Volts. Yes, emissions, lifespan, and performance are all affected by the filament voltage, and in part this tolerance is why some tubes fail before others, and possibly why some audiophiles roll tubes until they find something that sounds just right to them. Tubes are far from an exact science, so while testing I agree it is important to get it “right”, but don’t get too hung up on the micro details. It’ll drive you nuts!

 

Bill

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[shlafferty]

I see what you're saying, that tubes vary in characteristics so much, why should we be concerned about having the filament voltage just right? And it's true in consumer applications of tubes, characteristics are expected to vary a lot. But what we are talking about here is test equipment. It might be perfectly okay to use a tube with 80% Gm for an amplifier but that doesn't mean it's okay to let a tube test have 9% error. Do you really want to give up 9% of your 20% margin because your test equipment is off?

[Bill van Dijk]

For the record, I do not disagree with you, I’m just trying to play devil’s advocate to highlight the tolerances in some of the specifications. On that note….

 

Why focus on the filament voltage? The argument can be made that the filament current is as, if not more important. In many applications (most notably TV sets) it is indeed the current that is controlled. If the heat produced in the filament is proportional to the electron emissions, and the resistance of the filament is known, than the current would be king. But I suppose that is the clinch, it is the filament resistance that is the variable. My power supply has a Amp meter as well, and for reasons you eloquently described earlier (measure filament Voltage at the socket, not at the regulator) the argument can be made to go with the current since that will be the same throughout the circuit (Kirchoff’s current law). No worries about losses in the wiring.

 

As I said, I am just throwing out food for thought, it is all too easy to get hung up on one issue and lose perspective of the larger picture. There is no clear right or wrong, do what works for you within the tolerances provided and you will be close enough. Calculating tolerances properly is a whole discipline in itself, and that is a subject for another time. Interesting discussion though, I hope it is making some readers think about this.

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[Craig Sawyers]

I’m not saying that, considering modern technology, we should not do the best we can in regulating heater voltage, (or current, or power). However the valve/tube testers of yesteryear, including the various AVO models, just set a nominal ac voltage for a typical current. So the unloaded transformer voltage was a little on the high side, to compensate for wiring resistance, switch resistance and transformer winding losses. Notice the rather wide tolerance limits too.

 

From the AVO IV service manual.

Craig

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[Arthur Grannell]

Craig,

  The information concerning the Avo tester is not surprising or unusual. The reality of "tube testers", no matter how complex or sophisticated, is that they are really only "good" at doing one thing. And that is; determining whether or not a tube under test is suitable for service. To the contrary, regardless of the number of knobs, meters and dials, they are unsuitable for revealing the actual electrical conduction characteristics of vacuum tubes. This is why modern, highly accurate methods of accessing tube characteristics, including "curves" have been developed, often with the final objective of "tube matching". Examples are, of course, the "utracer" and Steve Lafferty's "VTA". The accuracy of these machines is directly dependent upon the techniques used in building them. If an accuracy of 10% or 20% is good enough, then certain shortcuts may be used. If higher accuracy is desired, then more complex (and possibly more expensive) techniques or circuits will be needed.

 

---ART---

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