LU1014D on ebay - how to test to prove it's not a fake? - diyAudio
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Old 8th April 2013, 05:08 AM   #1
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Default LU1014D on ebay - how to test to prove it's not a fake?

Hi all,
I impulse bought some LU1014D's off ebay - they were reasonably priced and as such I took a punt and bought twenty of them. Now I've just received them, and it seems prudent to test them first before issuing positive feedback to the seller.

What procedure would you all suggest? I just Idss checked a pile of j310's and 2sk170's yesterday, as described here Transistor matching so do I need to alter this approach significantly to test the LU1014D's? I'm about to check the datasheet but it seems helpful to the community at large to tap the collective wisdom here...

Cheers all!

...oh photo attached of the wee fellas.
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File Type: jpg LU power jfet.jpg (38.8 KB, 387 views)

Last edited by aspringv; 8th April 2013 at 05:09 AM. Reason: clarity, and I'm a numpty
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Old 8th April 2013, 05:58 AM   #2
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I hate to be a wet blanket, but I suspect that the parts you have are fakes. The very first thing you should do is connect gate to source on one of them, put 100 ohms or so in series with the drain for protection, and bias it up with a power supply or a 9V battery and a multimeter to measure current. If they don't conduct with gate shorted to source, they're fakes, plain and simple. Other tests can follow after that. There never were that many of those jfets out in the world, and certainly none since the company where I work absorbed Q-speed (a few years ago), hence my suspicion.
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Old 8th April 2013, 06:01 AM   #3
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Will do asap. I was dubious also but figured id take a shot and see. Worst comes to worst it'll be a paypal dispute.

Ill test now and get back asap.
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Old 8th April 2013, 06:40 AM   #4
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Originally Posted by aspringv View Post
...oh photo attached of the wee fellas.
Based on that picture => 99% sure they are fake.
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Old 8th April 2013, 06:50 AM   #5
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Default Testing

so tested with 100R on drain, test voltage of 9.1V, measured 8.88V across the resistor.

What is the range of current to be expected in this test with this part? (checks datasheet...)

Last edited by aspringv; 8th April 2013 at 07:10 AM. Reason: overly confident... :)
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Old 8th April 2013, 06:54 AM   #6
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photo didn't make out text on part. Will break out a camera with a macro function asap.

...and there it is.
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File Type: jpg LU upclose.JPG (97.4 KB, 352 views)

Last edited by aspringv; 8th April 2013 at 07:09 AM.
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Old 8th April 2013, 07:20 AM   #7
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photo didn't make out text on part. Will break out a camera with a macro function asap.
The text does not matter much as the legs are too long and the shape are slightly wrong. If you take new photos - take one of the rear side too..

I received LU1014Ds two times from Lovoltech and two times from Q-speed and all I received have had identical physical appearance..

To test the devices: Ground the gate, connect drain to ca. 3 volt and source via a resistor to ground. Over the resistor you should measure ca. 1.5 volt (1.2 to 1.8) depending on the resistor value.
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Old 8th April 2013, 07:31 AM   #8
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done - quick and rough, so I'll recheck, but using 100R resistor on source, reading 1V approx across resistor... using cheap and nasty old multi - will head to shed to get nice one...

More photo's to follow.
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Old 8th April 2013, 07:40 AM   #9
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Redid, showing approx 1.5V across 100R. Voltage wandered around a bit tho... Suspect the previous readings reflect a 2.8V or so supply as I recalibrated it for this one
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Old 8th April 2013, 08:06 AM   #10
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Redid - better setup - shows ~1.1V across 100R source resistor at 3.003V on drain.

Will test with another unit and will rephoto asap.
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