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 Post subject: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 12:07 pm 
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Location: Michigan
Does anyone know which meters do a decent job of accurately measuring transistor hfe? The only meter I have that measures hfe is a cheap Cen Tech from Harbor Freight, but it gives higher reading than what was provided by Small Bear. I'm guessing mine is not very accurate. Thanks.


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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 12:12 pm 
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Location: Richland, WA.
Are you measuring Ge transistors? If so, make sure they are somewhere in the 70's Fahrenheit. Temperature has a noticeable effect on Ge transistors. Even holding them in your hand too much will change the values.

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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 12:17 pm 
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If you're measuring hFE for a germanium transistor, you will get not only the gain but also the current leakage of the transistor, leading to an artificially high result. Most Ge trannies have significant leakage, so this error can be considerable. Small Bear corrects for the leakage in the value they report. Here's an article on how this correction is determined: http://www.geofex.com/article_folders/ffselect.htm

And as Nick said, the hFE measurement of Ge transistors is STRONGLY temperature dependent, so I recommend handling them with pliers or forceps.

Silicon transistors don't have these current leakage or heat sesnitivity problems, so if you're measuring one of those, you can ignore the first part of this post!

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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 12:47 pm 
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g-man wrote:
Does anyone know which meters do a decent job of accurately measuring transistor hfe? The only meter I have that measures hfe is a cheap Cen Tech from Harbor Freight, but it gives higher reading than what was provided by Small Bear. I'm guessing mine is not very accurate. Thanks.


Check out the Atlas DCA meters. They are great tools.


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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 1:39 pm 
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woolie wrote:
g-man wrote:
Does anyone know which meters do a decent job of accurately measuring transistor hfe? The only meter I have that measures hfe is a cheap Cen Tech from Harbor Freight, but it gives higher reading than what was provided by Small Bear. I'm guessing mine is not very accurate. Thanks.


Check out the Atlas DCA meters. They are great tools.

Use one, myself. Highly recommended.

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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 5:00 pm 
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Joined: Thu Feb 04, 2010 11:25 am
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Location: Michigan
Thanks guys. These are Ge trannies, and I didn't think about the leakage adding to the number. And yes I was holding them by the metal can, so maybe the extra heat was a factor too.


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 Post subject: Re: Meter to measure hfe
PostPosted: Tue Apr 17, 2018 5:43 pm 
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g-man wrote:
so maybe the extra heat was a factor too.


We have an IR thermometer that we use to try to make sure the transistors are around room temp (somewhere in the low to mid 70's). During the summer, we even go so far as to try to leave them under the AC outlet for a while before testing. That said, to answer your question more directly, the Atlas meters haven't let us down yet. Great tools for the job.

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