Best matching would be at the amplifier operating point. But that is not always possible so match as close as your tracer can get and call it a day.
You want to match Vgs for a given Iq and Vds.
Since you have an operating amplifier, you can measure those parameters.
You want to match Vgs for a given Iq and Vds.
Since you have an operating amplifier, you can measure those parameters.
best to match them at Iq prescribed for exact circuit, measuring Ugs
if only lower level of Iq for matching is possible, that's also usable, matching "tracking" is pretty good, by experience
but, take that lower level isn't extremely lower than prescribed (in circuit)
you'll find plenty of info on Articles page of FW site
in short - everything as Ben said
if only lower level of Iq for matching is possible, that's also usable, matching "tracking" is pretty good, by experience
but, take that lower level isn't extremely lower than prescribed (in circuit)
you'll find plenty of info on Articles page of FW site
in short - everything as Ben said
Thanks for the tips guys. As you pointed out ZM, correct; curve tracer gets to about 500mA and that's it. So I'm matching them at the highest point.
BTW, if you have not tried the Fairchild (now ON Semi) FQA28N15, consider as a very good alternative. They finally came back in stock at Mouser and Newark, but they are scheduled for obsolescence. I bought a couple of tubes, and had a tube of the Fairchild parts from about 2012. The datasheet says "suitable for audio amplifiers". Interesting note that I found out these are the power devices used in one of the Accuphase Class A power amps. I had the PDF brochure that was showing the internals of the amp and I did a zoom and clean up and you could see it was that part number. If I can find that I'll post it here.
BTW, if you have not tried the Fairchild (now ON Semi) FQA28N15, consider as a very good alternative. They finally came back in stock at Mouser and Newark, but they are scheduled for obsolescence. I bought a couple of tubes, and had a tube of the Fairchild parts from about 2012. The datasheet says "suitable for audio amplifiers". Interesting note that I found out these are the power devices used in one of the Accuphase Class A power amps. I had the PDF brochure that was showing the internals of the amp and I did a zoom and clean up and you could see it was that part number. If I can find that I'll post it here.
Attachments
Thx @TungstenAudio! I just put 100 in my cart, but am wondering if anyone would like to split some?
These parts have high enough transconductance and power dissipation to consider using as singles rather than matched pairs in the Aleph J. I did something similar with the Aleph J SS boards. That worked really well. My combo was IRFP048 above and FQH44N10 below.
The FQA28N15 should work well in both positions. They like 1.5A bias.
The FQA28N15 should work well in both positions. They like 1.5A bias.
Yup,That’s Crazy!!
There was 5317 available at Mouser 3 days ago when I last checked 😳
When I checked Wednesday, there was about 1500. I don't think Newark has changed they were around 800.
Also check arrow.com, hey have 1538 pieces today, decent price.
https://www.arrow.com/en/products/fqa28n15/on-semiconductor
This is a good website to check for semis:
https://www.trustedparts.com
https://www.arrow.com/en/products/fqa28n15/on-semiconductor
This is a good website to check for semis:
https://www.trustedparts.com
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