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Matching transistors. How to go about it?

D

doffo

Sr. Member
Oct 14, 2012
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I did get myself one of them cheap testers off eBay. Was going through some transistors to try and match some sets of 4. After looking here, it says that turn-on voltage or "Vth" is the value you want to match. My question is, what if one transistor is 1.74v and the next transistor tests 1.75v? Does that mean a .01v difference is enough that it isn't a match? Unsure if there was any variance in the voltage and it would still be ok to use in a set.

Any help on this would be greatly appreciated. Thanks for reading. :)
 
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Consider that a measurement in steps of 0.01 Volt has an uncertainty more or less equal to this lower limit. A difference that small just isn't significant. The rule for matching is the closer the better. We test a batch of 20 or 50 and mark the last digits on the rear. They get paired up by the reading. A matched pair usually has the same value within .02 or .03 Volt. Mostly you just want to avoid wiring up a pair that are really far off from one another. Then again, if you have a separate bias trimpot for each transistor, this is a lot less critical since they can each be set for correct idle current separately. Matching is most important when two transistors are wired together with only one bias-voltage adjustment feeding both transistors together.

73
 
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nomadradio said:
Consider that a measurement in steps of 0.01 Volt has an uncertainty more or less equal to this lower limit. A difference that small just isn't significant. The rule for matching is the closer the better. We test a batch of 20 or 50 and mark the last digits on the rear. They get paired up by the reading. A matched pair usually has the same value within .02 or .03 Volt. Mostly you just want to avoid wiring up a pair that are really far off from one another. Then again, if you have a separate bias trimpot for each transistor, this is a lot less critical since they can each be set for correct idle current separately. Matching is most important when two transistors are wired together with only one bias-voltage adjustment feeding both transistors together.

73
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Appreciate it. That gives a good window if it can be .02v-.03v from one another.
 

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