Grid loupe PCBs

[Ihor Smal]

Hi All, 

Recently I built the utracer and wanted to have the 'grid loupe' (described in the Ronald's logbook) as well. So I decided to learn PCB design using Eagle and that scheme. I ordered the PCBs (at Seeeds) but the minimum batch was 10 PCBs. The one that I assembled works great. The rest I do not really need and willing to give away for symbolic price of 1 euro (to compensate my two days of messing up with Eagle) + the shipping costs to your destination. The shipping costs are listed here: https://www.postnl.nl/en/mail-and-parcels/mail/international-mail/  Let me know if you are interested. 

[Ihor Smal]

The actual schematics and the board layout is also attached.

[Rudie Dorrepaal]

Hi Ihor,

I am very interested in buying one of you.

I am Dutch but live in Dublin, Ireland.

Please let me know how much money to transfer to you.

Regards,

Rudie

Op vr 15 nov. 2019 02:15 schreef Ihor Smal <iste...@gmail.com>:

Hi All, 

Recently I built the utracer and wanted to have the 'grid loupe' (described in the Ronald's logbook) as well. So I decided to learn PCB design using Eagle and that scheme. I ordered the PCBs (at Seeeds) but the minimum batch was 10 PCBs. The one that I assembled works great. The rest I do not really need and willing to give away for symbolic price of 1 euro (to compensate my two days of messing up with Eagle) + the shipping costs to your destination. The shipping costs are listed here: https://www.postnl.nl/en/mail-and-parcels/mail/international-mail/  Let me know if you are interested. 

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[AllThumbsTom]

Hello Ihor:

Thank you so much for bringing the Grid Loupe to me attention!
I didn’t know about it.
Can you put me on your list to buy one?
Would 10 euros be ok or let me know.
I live in Oregon, USA. Zip Code 97267

Tom M

[Ihor Smal]

Hi Tom, 

You are welcome. Out of a few extensions that Ronald mentioned on his website that grid loupe was the most useful for me. It has two benefits, one is that you can measure grid current if you are into design of AB2 amps, but more importantly it is more accurate for generating low grid voltages (between 0 and -10) compared to the native uTracer capabilities (because those are scaled from 0 to -50) from the same source of PWM signal of 5V. 

In any case, good to hear that you are interested. 10 euro would be way more than I asked, but you are welcome to “donate” :) still not so much. What I counted before was 2.9 euro shipping to the US and 1euro for the PCB, so the total in $4.30. The Seeed service of printing PCBs is not expensive (about $6 for 10 PCBs) but the shipping costs were 12 euros. 

My paypal is ih...@gmx.co.uk

Also, if you are interested about this “crazy” accurate power supply, I also have 5 of those PCBs. I can send you one for free. The schematics and description is on this website: http://tronola.com/html/tube_analyzer_you_can_build_page1.html

The guy posted the PCBs files which can be directly uploaded to Seeeds and ordered but then again one get 5 pieces and it is too much. 

 

Cheers, 

Ihor

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[shlafferty]

Hi Ihor,

Thank you so much for offering the Grid Loupe PCBs! I have sent payment for one via PayPal. (I sent about 10 euro to make sure all your costs are covered.) The PCB layout looks very nice.

I would also like to thank you for offering the PCBs for the "crazy accurate" heater supply I wrote about on Tronola.com. I'd hoped someone would do that.

Bravo for helping support folks interested in Dr. Dekker's awesome uTracer!

Sincerely, Steve Lafferty

http://www.tronola.com/

[mman...@fuse.net]

Hello All,

I built Ronald's grid loupe on pad-per-hole prototype board. It functions as expected except that it has an offset in indicated grid current of ca. 180 uA. My uTracer's screen supply shows zero current when it is left open, but reads this phantom current when it is connected to the grid loupe's output transistor. 

Has anyone else observed this?

Martin Manning

---

From: "Ihor Smal" <iste...@gmail.com>
To: "uTracer" <utr...@googlegroups.com>
Sent: Friday, November 15, 2019 5:03:43 AM
Subject: Re: Grid loupe PCBs

The actual schematics and the board layout is also attached.

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[Ihor Smal]

I will be able to check my grid loupe only next week, right now I am in the middle of installing the utracer with all the parts into a chassis. Just out of curiosity, what voltage do you apply to the Screen/(transistor collector) in that case? Is it recommended 20V ? Also do you actually measure approximately 18mV on the emitter/R11 resistor (which is 100 Ohm)? Just to know if it is physically there or it is a reading noise of the utracer. 

Also in Ronald's logbook in "14. Higher Currents I: Exploring the Limits" it says something about the resolution of the current sensing part:

"Since we are using only a 10 bit ADC to measure the currents, extending the current range to for example 1A reduces the resolution from 0.2 mA/bit to 1 mA/bit." 

So your measurement is the next possible measurement after exact 0. The next possible value is 0.4mA and so on.... so basically you are at the noise floor I would say. 

  

On Saturday, November 16, 2019 at 3:26:14 PM UTC+1, mman...@fuse.net wrote:

Hello All,

I built Ronald's grid loupe on pad-per-hole prototype board. It functions as expected except that it has an offset in indicated grid current of ca. 180 uA. My uTracer's screen supply shows zero current when it is left open, but reads this phantom current when it is connected to the grid loupe's output transistor. 

Has anyone else observed this?

Martin Manning

---

From: "Ihor Smal" <iste...@gmail.com>
To: "uTracer" <utr...@googlegroups.com>
Sent: Friday, November 15, 2019 5:03:43 AM
Subject: Re: Grid loupe PCBs

The actual schematics and the board layout is also attached.

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[Ihor]

Actually in my first post above, the first screenshot with the measurements also shows that for negative grid voltages, the measured grid current (which is indicated as Is) is not zero but is about 0.2-0.3mA (it is difficult to see the exact value there, but it is definitely lower than 0.5mA). 

[mman...@fuse.net]

Yes I noticed that. It looks like you are showing about 333 uA. The current measurement seems capable of much finer resolution than that, as seen by the slight increase in grid current at 0V Vg as Va approaches 0V. If you connect a 10k resistor between the grid terminal and the cathode, and do a grid voltage sweep from 0-5V I think you you will see that the slope is correct, but the grid current is not zero at 0V Vg. I have been using 30V Vs, which seems to smooth out the grid current trace a little better than the 20V Ronald recommended. 

MPM

---

From: "Ihor" <iste...@gmail.com>
To: "uTracer" <utr...@googlegroups.com>
Sent: Saturday, November 16, 2019 5:36:07 PM

Subject: Re: Grid loupe PCBs

Actually in my first post above, the first screenshot with the measurements also shows that for negative grid voltages, the measured grid current (which is indicated as Is) is not zero but is about 0.2-0.3mA (it is difficult to see the exact value there, but it is definitely lower than 0.5mA). 

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[Ihor]

I still have to do the test with a resistor, also as Ronald described in his Lab Notebook. Interestingly, there his has perfect 0 measurements for the linear plot with the resistors, as ell as zero grid current for E188CC:

On Sunday, November 17, 2019 at 12:27:40 AM UTC+1, mman...@fuse.net wrote:

Yes I noticed that. It looks like you are showing about 333 uA. The current measurement seems capable of much finer resolution than that, as seen by the slight increase in grid current at 0V Vg as Va approaches 0V. If you connect a 10k resistor between the grid terminal and the cathode, and do a grid voltage sweep from 0-5V I think you you will see that the slope is correct, but the grid current is not zero at 0V Vg. I have been using 30V Vs, which seems to smooth out the grid current trace a little better than the 20V Ronald recommended. 

MPM

---

From: "Ihor" <iste...@gmail.com>
To: "uTracer" <utr...@googlegroups.com>
Sent: Saturday, November 16, 2019 5:36:07 PM
Subject: Re: Grid loupe PCBs

Actually in my first post above, the first screenshot with the measurements also shows that for negative grid voltages, the measured grid current (which is indicated as Is) is not zero but is about 0.2-0.3mA (it is difficult to see the exact value there, but it is definitely lower than 0.5mA). 

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[mman...@fuse.net]

At one point I changed the op amp and the phantom current was reduced from ~300uA to <200uA. I wonder if this is an op amp offset issue?

Another observation I have made is that if a low-Vg set-up is saved and then recalled, the step and sweep variable values are reset to the defaults. Have you seen this?

MPM

----- Original Message -----
From: Ihor <iste...@gmail.com>
To: uTracer <utr...@googlegroups.com>
Sent: Sun, 17 Nov 2019 04:02:56 -0500 (EST)
Subject: Re: Grid loupe PCBs

I still have to do the test with a resistor, also as Ronald described in
his Lab Notebook. Interestingly, there his has perfect 0 measurements for
the linear plot with the resistors, as ell as zero grid current for E188CC:

On Sunday, November 17, 2019 at 12:27:40 AM UTC+1, mman...@fuse.net wrote:
>
> Yes I noticed that. It looks like you are showing about 333 uA. The
> current measurement seems capable of much finer resolution than that, as
> seen by the slight increase in grid current at 0V Vg as Va approaches 0V.
> If you connect a 10k resistor between the grid terminal and the cathode,
> and do a grid voltage sweep from 0-5V I think you you will see that the
> slope is correct, but the grid current is not zero at 0V Vg. I have been
> using 30V Vs, which seems to smooth out the grid current trace a little
> better than the 20V Ronald recommended.
>
> MPM
>

> ------------------------------
> *From: *"Ihor" <iste...@gmail.com <javascript:>>
> *To: *"uTracer" <utr...@googlegroups.com <javascript:>>
> *Sent: *Saturday, November 16, 2019 5:36:07 PM
> *Subject: *Re: Grid loupe PCBs

>
> Actually in my first post above, the first screenshot with the
> measurements also shows that for negative grid voltages, the measured grid
> current (which is indicated as Is) is not zero but is about 0.2-0.3mA (it
> is difficult to see the exact value there, but it is definitely lower than
> 0.5mA).
>
> --
> You received this message because you are subscribed to the Google Groups
> "uTracer" group.
> To unsubscribe from this group and stop receiving emails from it, send an

> email to utr...@googlegroups.com <javascript:>.

> To view this discussion on the web visit
> https://groups.google.com/d/msgid/utracer/38933ad6-102a-4916-87f8-53e05bf8f736%40googlegroups.com

> <https://groups.google.com/d/msgid/utracer/38933ad6-102a-4916-87f8-53e05bf8f736%40googlegroups.com?utm_medium=email&utm_source=footer>
> .

>
>

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[jgx plato]

Hi ihor, thanks for the pcb grid loupe pcb, there is posible send one to Spain? Please let me know if it posible, and the cost including shipping to Spain and I will pay with PayPal!

Regards

jgxbos

[Ihor]

Hi Martin, 

I finally had a bit of time to put my uTracer in a box and start experimenting once again. Previously I had that 0.3mA offset measured by the gridloupe even when the grid did not conduct any current. Right now I have 4 pieces of LM348 and I think I was extremely unlucky with the first one that I took and put in my gridloupe. Today I tested 3 others and all of them gave 0.003mA offset, see the attached images for comparison. The tube is 6N23P and it is deeply in the non-conductive state where the grid current is zero. 

Cheers, 

Ihor

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[mman...@fuse.net]

Thanks, I have a a couple more LM348 to try, so I'll see if I can find a good one. The ones I have are TI's, from Mouser, probably all from the same lot.

Have you noticed a failure to save the set-up file correctly when Low Vg is selected? I have noticed that when I recall the set-up the sweep and step variables have been reset to the defaults.

MPM

---

From: "Ihor" <iste...@gmail.com>
To: "uTracer" <utr...@googlegroups.com>

Sent: Friday, January 3, 2020 12:35:59 PM

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[Pete Doxat]

Hi Ihor,

Do you still have some of the PCB's available? I'm in the UK and would love to add this functionality. Please let me know. Cheers!

Pete

[Ihor]

Thanks, I have a a couple more LM348 to try, so I'll see if I can find a good one. The ones I have are TI's, from Mouser, probably all from the same lot.

I bought mine at Reichelt (you can search for "LM 348 DIL" there) but they are also from TI. It would be interesting to see what you get with your samples. In my case, it looks like there is quite a huge difference between "good" and "bad" samples: I have 3 very good and one really bad, nothing (uniformly) in between. If you do not succeed in finding a good one among yours, I can send you one of mine. 

 

Have you noticed a failure to save the set-up file correctly when Low Vg is selected? I have noticed that when I recall the set-up the sweep and step variables have been reset to the defaults.

I forgot to answer it the first time, indeed I observed the same thing: the settings for Va and steps for Vg are not saved properly when the Vlow checkbox is activated, even though the state of that checkbox is saved/restored properly.  

MPM

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[Ihor]

I still have a few but they are almost gone. I've sent you a PM with details, but for people who wants to get those boards in the future, or in larger amounts I am posting here the gerber files, so one can order those PCBs from China themself. You can go to the https://pcbshopper.com and get the estimates of the costs, they will depend on how busy the factory is right now, if they have any discounts and the shipping costs to your country and the minimum amount of PCBs that they force you to buy (usually 5 or 10). I myself tried 3 services: seeedstudio, jlcpcb and elecrow (you will see them suggested by the pcbshopper.com) and the quality is everywhere the same. There are some nice discounts for newcomers (you can get 5 PCBs for 2-3$ with shipping) but most of the time it will cost you 7-14$ (incl. shipping) anyway. On the screenshot you can also see some of the parameters that you might need to specify while making the order (submitting the .zip archive). 

Cheers, 

Ihor

[jgx plato]

Hi Steve Lafferty and Ihor:

I am mounting the "crazy acccurate" heater supply (Thanks Ihor for the PCB, in few days I will mount the grid loupe too!), and I have two doubts:

1) The value of R211 is 2.7K or 270Ohms? In the BOM, the mouser reference (CF1/4C271J) match  to a resistence of 270 Ohms, but in the schematics R211 have a value of 2.7K. Moreover, in the photo of the pcb mounted in tronola, I can see the color code of the resistence R211 and seems red, violet brown (270 ohms). What are the correct value for R211?

2) I can't see the position of C207 (0.22uF/50V) in the PCB of heater supply of tronala, is a mistake? I have to  solder C207 out of pcb? Is important C207?

Regards

jgxbos

[shlafferty]

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 if 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 to improve 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. (Press your End key to go to the last slide and hold Left Arrow to go back 6 slides.)

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

All the best,

Steve Lafferty

http://www.tronola.com

[jgx plato]

Thanks Steve!

All is clear now!. No problem I have 2.7K resistors at home! Regarding the C207, it’s clear to me  too. 

Thank you to the excelent word with your heater supply, I will use your design to replace a Chinese buck converter. I will try to make some modification  to add a variable output, the 6.3 and 12.6V are usually used by me, but some tubes require 2.5V or other voltages...

Again, thanks for your fast feedback! And, please keep safe at home from Coronavirus, here in Spain it is being a nightmare for so much families! Don’t underestimated this threat!

Best regards

Juan

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[shlafferty]

Hi Juan,

I'm glad that info helped and thank you for the kind words and the COVID-19 warning. I'm so sorry that Spain has experienced such a tough time with it. I hope it turns around soon and that you stay well. The new hydroxychloroquine/azithromycin combination looks very promising. Folks are taking the virus very seriously here.

I have a few thoughts about modifying the heater regulator board for other or variable output voltages but I'm concerned that some might think we're hijacking this Grid loupe PCB thread if we carry on here. So I will post those thoughts in the Reader Comments section of the Tronola article. http://www.tronola.com/html/tube_analyzer_you_can_build_page1.html

Steve