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Old 5th February 2013, 05:08 PM   #21
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Originally Posted by Semisouthfan View Post
As promised, attached is the first article entitled "Is it SemiSouth?" This is my attempt to contribute to the understanding of what is inside the TO247 package and how to feel confident that you have a genuine SemiSouth JFET.

I have tried to balance my professor's instinct to bathe you in technical details with my own realization that I would prefer you to find this interesting. Only you will be judge of that, but if it seems a bit corny, please have mercy.

Next up will be an article on what I have learned about the native linearity of SemiSouth JFETs and my personal thoughts on simulation, with the goal of making available relatively simple methods for estimating the performance of SemiSouth JFETs in real circuits.
Great article, and for trouble shooting too. A while ago, Mr. Pass built a Plasma Loudspeaker. I still can see a picture of him next to it. Concern with O3 came up.
Best regards.
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Old 5th February 2013, 06:28 PM   #22
generg is offline generg  Germany
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Originally Posted by Zen Mod View Post
luckily - all Generg's SS are already tested in vivo

that´s my man, exactly.....

4 from Magura, 8 from tea-bag and 8 from Roger combined in endless variations and circuits..... they look like old men, but they are still all working,

Oh, one was lost by failure and two went to a friend for an F2J....



Nevertheless I am very grateful for the article because my DMM measured always nothing and I did not know if I killed one or not... when there was no sound again...

now I can measure with resistors, battery and "billig" DMM following the advice of Semisouthfan these suspect candidates......
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Old 5th February 2013, 08:58 PM   #23
Zen Mod is offline Zen Mod  Serbia
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just from top of my head - I'm not too much of responsible in late hours ( so - never ) - one can augment DMM with one 1V5 cell , polarized properly in series with one of the probes
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Old 5th February 2013, 10:33 PM   #24
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Default Power supply/battery approach for diode checking

Given the amount of feedback on the DMM approach, I decided to post a picture of me making the same measurement using the power supply approach, this time on a SJEP120R125. In the image you will see my hands probing the gate and source pins of the part and measuring the voltage drop with the Fluke 87. Next to the Fluke is a lab power supply with 8.4 V on the front panel. This simulates nicely a humble 9 V battery which could be used to make the same test. A 2.7 kOhm resistor can be seen suspended by alligator clips between my hands and below the part. The measured forward voltage drop is 2.549 V. I get the same value measured gate to drain for the same power supply voltage and resistor.

The diode checker on this Fluke 87 measured 2.489 V, highlighting what can be seen in the original article, namely, that the forward bias curve of the diode is exponentially rising but still dependent on the exact value of current flowing. The diode checker measured about 7.7 V open circuit voltage.

The bottom line is that diode checkers are not designed for such a high built-in potential. When in doubt, substitute a battery and resistor (a few kiloOhms is perfect) in series with the junction and measure the voltage dropped across the junction.
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Old 5th February 2013, 10:41 PM   #25
Zen Mod is offline Zen Mod  Serbia
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considering good common engineering praxis , all those you dropped from the bench on the floor , you can send for proper disposal - to Official PL Disposal Facility

ZM
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Old 6th February 2013, 01:01 AM   #26
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Originally Posted by Zen Mod View Post
considering good common engineering praxis , all those you dropped from the bench on the floor , you can send for proper disposal - to Official PL Disposal Facility

ZM
Official PL Disposal Facility
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Clever, very clever.
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Old 6th February 2013, 01:15 AM   #27
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Originally Posted by Antoinel View Post
Great article, and for trouble shooting too. A while ago, Mr. Pass built a Plasma Loudspeaker. I still can see a picture of him next to it. Concern with O3 came up.
Best regards.
Yep, that devilish OAP (one atmospheric pressure) glow discharge in air will fill a room with O3 if you aren't careful. The well known "Hill Type 1" fixed this problem using Helium. "Fixed," that is, if you think re-ordering a bottle of helium to keep your tweeter running is practical.

But helium, besides controlling the O3, has another crucial advantage. If you read my paper, you'll see what I mean.

My paper was inspired by Alan Hill, whom I had the pleasure of meeting in person and talking plasma speakers with way back when. He told me to look up his patent. I did. It was amazing and the paper I wrote was based on a derivation that he published in the patent. (Most unusual...)
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Old 6th February 2013, 05:57 AM   #28
Gyuri is offline Gyuri  Hungary
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Quote:
Originally Posted by Semisouthfan View Post
Given the amount of feedback on the DMM approach, I decided to post a picture of me making the same measurement using the power supply approach, this time on a SJEP120R125. In the image you will see my hands probing the gate and source pins of the part and measuring the voltage drop with the Fluke 87. Next to the Fluke is a lab power supply with 8.4 V on the front panel. This simulates nicely a humble 9 V battery which could be used to make the same test. A 2.7 kOhm resistor can be seen suspended by alligator clips between my hands and below the part. The measured forward voltage drop is 2.549 V. I get the same value measured gate to drain for the same power supply voltage and resistor.

The diode checker on this Fluke 87 measured 2.489 V, highlighting what can be seen in the original article, namely, that the forward bias curve of the diode is exponentially rising but still dependent on the exact value of current flowing. The diode checker measured about 7.7 V open circuit voltage.

The bottom line is that diode checkers are not designed for such a high built-in potential. When in doubt, substitute a battery and resistor (a few kiloOhms is perfect) in series with the junction and measure the voltage dropped across the junction.
So, I think here is a solution:
The short circuit currents all of my DMM's only circa 1 mA, in diode check.
If I compute it correctly, in your very nice setup (which is the peak of the electrical engineering sciences) there is about 2 mA.
Am I right?


Ah, it is only now come in my mind, your Fluke 87 has a 7.7V open circuit voltage, what I supposed earlier.

Wacky Gyuri
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Old 6th February 2013, 12:45 PM   #29
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Originally Posted by Gyuri View Post
So, I think here is a solution:
The short circuit currents all of my DMM's only circa 1 mA, in diode check.
If I compute it correctly, in your very nice setup (which is the peak of the electrical engineering sciences) there is about 2 mA.
Am I right?


Ah, it is only now come in my mind, your Fluke 87 has a 7.7V open circuit voltage, what I supposed earlier.

Wacky Gyuri
As Gyuri pointed out, I worked overtime on the design of that circuit.

With respect to the short circuit current, possibly, as it can be an indicator of too low open circuit voltage. Strictly speaking, 1 mA would measure differently by perhaps only a few tens of millivolts. The issue is open-circuit voltage and possibly a threshold condition built into the DMM hardware (speculation). The current available at 2.6 V is much less than 1 mA if the open circuit voltage is around this value. Then the bias current will fall off exponentially and the DMM may shrug it's shoulders (in a manner of speaking) and call it an open circuit.

The short circuit current in my marvel of electrical engineering science is 3.1 mA (8.4 V / 2.7 kOhm). At the measured diode drop of about 2.6 V the bias current was 2.1 mA as you suggest. The difference is that 2.6 V is not a short circuit, but with 8.4 V of open circuit potential, it is not a problem. DMM's commonly have less than about 3 V of open-circuit potential (the designer was expecting 0.7 V or maybe 1 V from an LED). The Fluke 87 is obviously not so limited and while my Fluke 16 worked, the values were more scattered reflecting that it barely had enough open circuit voltage.
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Old 6th February 2013, 01:22 PM   #30
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Did SemiSouth tank as it was "sole-source"?
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