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Old 7th December 2005, 03:13 PM   #11
tmblack is offline tmblack  United Kingdom
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I have a bunch of 2N3819 JFETs with Vp from -1.3 to -2.97V.
How well do they need to be matched for a differential front end?

Also gathering 2SK170'BL's. How much variance are there and how much can I tolerate when paralleling 4 of them?

Tom

EE
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Old 23rd December 2013, 06:54 PM   #12
Turbon is offline Turbon  Sweden
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Quote:
Originally Posted by john curl View Post
I hope that Nelson has shown how to do this, BUT it is fairly easy with just a multimeter. You just short the gate to the source and add a 9V battery from the drain to the source. This gives you Idss. But how to measure? Put a 10 ohm resistor between the drain and the battery and measure across it. 0.1V=10ma and so forth. Matching Vbe is much more difficult.
Following this guide looking at the datasheet for 2sk170bl - 0,00v over 10 Ohms... Tried 4 of them now. Maybe the battery is old. Even moved everything down my experiment board - no dice...

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Old 23rd December 2013, 07:38 PM   #13
Turbon is offline Turbon  Sweden
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Originally Posted by Turbon View Post
Following this guide looking at the datasheet for 2sk170bl - 0,00v over 10 Ohms... Tried 4 of them now. Maybe the battery is old. Even moved everything down my experiment board - no dice...

Regards
Battery broken...

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Old 23rd December 2013, 11:18 PM   #14
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Quote:
Originally Posted by john curl View Post
I hope that Nelson has shown how to do this, BUT it is fairly easy with just a multimeter. You just short the gate to the source and add a 9V battery from the drain to the source. This gives you Idss. But how to measure? Put a 10 ohm resistor between the drain and the battery and measure across it. 0.1V=10ma and so forth. Matching Vbe is much more difficult.
The Nelson Pass page with explanations and diagrams is "Matching Devices" at https://www.passdiy.com/project/arti...tching-devices

My atch diagram is taken from a circuit simulator (Multisim) but illustrates the concepts.

Dale
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