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Old 25th February 2012, 03:21 PM   #31
EUVL is offline EUVL  Europe
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Firstly let's see if we agree that we only need to measure tubes at > 100V.
If we do not agree, then I rest my case.

If we agree, then this is how I would do it with your current hardware :

1) Connect the cathode of the tube to the C-channel. Set Vch to say 12V.
2) Connect the grid to the B-channel. This will allow a negative grid voltage up to -10V relative to cathode. B-channel in voltage mode.
3) Connect the E-channel to an opamp driving an output stage as described in post#29. The E-channel rail can be as high as the Mosfets will take.

You need to change some software, but you can now measure current (inverted) using Rc. And Grid voltage is, if I am not wrong (I checked Linsley Hood's books just now) always negative to cathode. So measuring grid voltage to cathode is no problem.

But perhaps some tube guy will tell you whether I am talking nonsense.


Patrick
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Old 26th February 2012, 02:50 AM   #32
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No, I want to measure transistors out to over 200v for some applications.
It is good to see where the breakdown voltage is in a given batch, especially if you are forced to work near the rated limits. Nice if you don't, but if you do... this happens often enough in high power amplifiers...

My Tektronix and Fairchild units will do 400vdc and 1000vdc respectively, which is fine.

Of course they do not "remember" anything, since they just do simple curve tracing.
The Tek can switch between two DUTs, but that too has it's limits.

What would be best is to be able to "slam" devices into a ZIF socket, quickly, push a test button, repeat, repeat, etc... and have all the curves recorded. Then put some parameters into a screen and have the results sorted by those parameters - the devices number being the order tested. So now I can just grab the devices according to the computer's sort by pulling the right numbers and have batches of matched devices!

That's the idea as far as I am concerned. If I have to look at the curves to compare devices, then I personally don't need a computer based curve tracer at all.

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Last edited by bear; 26th February 2012 at 03:11 AM.
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Old 26th February 2012, 03:05 AM   #33
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Power tubes can draw current on the grid when driven hard into A2 or AB2... a few watts is typical... most tests do not need this.
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Old 26th February 2012, 09:41 AM   #34
locky_z is offline locky_z  China
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Most Tube is like N type J-FET in normal voltage, but if work in low voltage,Tube like some BJT.

I had used CT3 to test some Tube in low Cathode-Anode voltage.
but under low Cathode-Anode voltage,Even if the gate voltage is 0, Most tube have no anode current.
you must give gate positive voltage,the tube will have some current,and the Gate current almost equal anode current.



Because High voltage and No P Type ,So this Intelligent Curve Tracer circuit not suit Tube test.
I plan designed another circuit to test Tube,Of course It will be considered to A2 and AB2 state, and measure the Anode current ,gate current and screen grid current.
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Old 26th February 2012, 01:39 PM   #35
mos57 is offline mos57  Italy
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I was able to view only the output curves of NPN Bjt, but not for PNP Bjt.

Also i cannot view the curves for Jfets. Your manual is not detailed enough.

Can you advice me for that?

Francesco
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Old 26th February 2012, 06:03 PM   #36
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Looking at the design a little more.

Why not make "C" amp run from + & - rails??
Put an inverter at the input for switching from Nch to Pch??
Put an inverter at the input of the Bch amp too??

If the input to both amps only runs in one polarity, then the output is only in one polarity?

Is there a reason not to do this?
I would think this is exactly the sort of thing that previous commercial curve tracers had to do?

Of course I am completely unclear on how one is supposed to operate the IT 3.0, but surely would like a DIY sort of unit that is computer controlled that can do batch testing with software sorting of the results.

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Old 27th February 2012, 12:05 AM   #37
locky_z is offline locky_z  China
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Quote:
Originally Posted by mos57 View Post
I was able to view only the output curves of NPN Bjt, but not for PNP Bjt.

Also i cannot view the curves for Jfets. Your manual is not detailed enough.

Can you advice me for that?

Francesco
You load 'PNP Vce-Ic' condition
and plug PNP in slot, Base insert B,Collect into C,Emitter into E,
and press 'GO!' button.

JFET is the same,load 'measure continue' and plug Gird into B,Source into E,Drain into C.
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Old 27th February 2012, 12:17 AM   #38
locky_z is offline locky_z  China
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Quote:
Originally Posted by bear View Post
Looking at the design a little more.

Why not make "C" amp run from + & - rails??
Put an inverter at the input for switching from Nch to Pch??
Put an inverter at the input of the Bch amp too??

If the input to both amps only runs in one polarity, then the output is only in one polarity?

Is there a reason not to do this?
I would think this is exactly the sort of thing that previous commercial curve tracers had to do?

Of course I am completely unclear on how one is supposed to operate the IT 3.0, but surely would like a DIY sort of unit that is computer controlled that can do batch testing with software sorting of the results.

_-_-bear
C Amp Output series a resistor in order to sample the collect current.

such as J-fet,Sit transistor they need a bipolar voltage, use siwtch to switch the power pole is complex

and the ADC need a bipolar type.
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Old 27th February 2012, 02:40 AM   #39
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A simple inverter circuit will convert the input going to the ADC from - polarity to + polarity??

Or is there a reason this will not work?

I must be confused about how this works.

No need to switch the power supply at all. Use an amp that is a DC coupled amp that can swing either plus or minus depending on the input supplied? This would be an electronic "switch". One would toggle all the necessary places simultaneously.

_-_-bear
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Old 27th February 2012, 03:32 AM   #40
locky_z is offline locky_z  China
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My CT3 Block diagram below
Click the image to open in full size.
It only need single supply, unbipolar ADC and DAC,




Another normal MCU curve trace Block diagram is below
Click the image to open in full size.
It need double polarity power supply,
And if ADC DAC is not bipolar,then need inverter.
If is more complex.
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