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.