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Old 8th September 2010, 12:16 AM   #271
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Default Yes, these should work

The two input transistors, the differential pair, these should be matched within 20 percent.

regards,

Carlos
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Old 8th September 2010, 03:23 AM   #272
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Originally Posted by a.wayne View Post
Carlos ,

Found the outputs at Mouser, these should work , correct ? ..



mjl1302a

mjl3281a


Do we have to use matched transistors ?


Regards,
If you buy all OP trannies at the same time from mouser they should be fairly close (2%) On- semi is consistant. Same for the input pair , same batch of transistors ..worst I have seen is 25mv offset (fairchild) 20% is not too good , would require a offset adjust trimmer to get even close.
OS
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Old 8th September 2010, 10:50 AM   #273
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A. Wayne,
Avnet express has the same transistor for 1.94. I have used them and there service is second to none. Really great company.


Order mjl3281 Parts Online, Download Datasheets, View Manufacturer Info at Avnet Express

Tad
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Old 8th September 2010, 11:17 AM   #274
AndrewT is offline AndrewT  Scotland
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The two input transistors, the differential pair, these should be matched within 20 percent.
which transistor parameter/s are you recommending be matched within 20%?
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Old 8th September 2010, 11:32 AM   #275
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Default The gain to DC, this one you measure using standard multimeters

If equal or within 20 percent with low voltage (from multimeter), may be also equal or within 20 percent while submited to higher voltage...off course the real gain number will be different while measure with low voltage compared to high voltage.

regards,

Carlos
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Old 8th September 2010, 01:34 PM   #276
AndrewT is offline AndrewT  Scotland
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Carlos,
say that in your first recommendation.

"Match hFE using a DMM transistor hFE test to within 20%."

However, I don't agree.

I would recommend that the DMM hFE be used to batch similar devices. Then test hFE properly at the current expected in the operational circuit. Match these properly measured hFE @ XmA of Ic to better than 5%.

Then a second parameter match even more important than the hFE match.
Measure the Vbe vs Ic of these hFE matched devices.
Use a dual transistor jig. Apply a fixed Vbe to both transistors and measure the Ic flowing through each. Adjust Vbe until Ic = operational current. Choose devices that when Thermally Coupled and with Identical Vbe and Identical Vce pass Ic within better than 1%. These make a matched pair at that Ic.

I go further.
I swing the Vbe slightly either side to get matching percentages over a range of currents, maybe +-20% of operating Ic. Again hoping to see Ic matching to better than 1% over the range of Ic that I have tested.
BTW,
I do my matched jFETs in a similar manner. They really match to the specification I give.

When I install these matched pair I find they amplify very well and have very low output offset. When in the circuit (if properly designed) they have very similar Vce and very similar Vbe.
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Old 8th September 2010, 03:52 PM   #277
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Default Oh!..... nice sophisticated super precise method...sorry..i am not that precise

or demanding.......i do accept things in electronics have tollerances..so, small variations to me is fine.

But of course, people are reading you, if they think it is a good idea, then they gonna use your suggestions for sure.

thank you,

regards,

Carlos
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Old 8th September 2010, 04:09 PM   #278
AndrewT is offline AndrewT  Scotland
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don't be sorry for not being precise in your selection of components. There is no reason to appologise.

But, be unambiguous when you tell your readers what you recommend.

As you can see "match transistors" means something completely different to different people.
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Old 8th September 2010, 05:40 PM   #279
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Originally Posted by tryonziess View Post
A. Wayne,
Avnet express has the same transistor for 1.94. I have used them and there service is second to none. Really great company.


Order mjl3281 Parts Online, Download Datasheets, View Manufacturer Info at Avnet Express

Tad
Thanks for the tip ...........
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Old 6th October 2010, 08:15 AM   #280
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Default This is the way i see the Troyan

A huge powerfull machine!

YouTube - Radial Engine Powered Goggomobil

regards,

Carlos
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