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WTB Matched pairs FQA12P20 / FQA19N20

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#2
Is your M2 a factory piece or a DIY one? If it's a factory M2, I believe the parts were FQA19N20C and FQA12P20.

Also, what did you mean by a matched quad? My understanding is that these P and N channel parts are somewhat different (not true complementary) and that you can't really match the N to P.
 
#3
Hi Dennis. It’s a clone M2, built with the IRFP devices in fact, but this seemed like a good opportunity to rebuild with the FQAs as I gather some prefer these.

I’m not sure on the matching question to be honest, just looking for a close tolerance set in the correct values for an M2.
 
#4
I’ve been speaking to a friend who is helping me fix the M2 and have a better idea of what we need re: the MOSFETs.

I’m looking for 2 x push-pull pairs that play nicely together for lowest DC offset, each pair would need to be matched to give L-R balance. Am more interested in quiet devices than high power.

Does that help?
 
#8
Realistically, the OP might look for one pair of NN matched mosfets and one pair of PP matched mosfets. N-P matching doesn't seem feasible (e.g. significantly difference in Vgs at a given current level)

DC offset is usually a matter of adjustment and thermal stability.

Noise in the M2 comes mostly from pick up from the input transformer and standard wiring/ground loop type issues. A working pair of output devices shouldn't be particularly noisy though perhaps some different output device models are quieter than others, and there could be variations within a model as well.
 
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#10
Dennis Hui said:
Realistically, the OP might look for one pair of NN matched mosfets and one pair of PP matched mosfets. N-P matching doesn't seem feasible (e.g. significantly difference in Vgs at a given current level)

DC offset is usually a matter of adjustment and thermal stability.

Noise in the M2 comes mostly from pick up from the input transformer and standard wiring/ground loop type issues. A working pair of output devices shouldn't be particularly noisy though perhaps some different output device models are quieter than others, and there could be variations within a model as well.
Click to expand...

Thanks Dennis… it looks like the parts Marra has are a suitable replacement, and were matched by Buzzforb using a curve tracer, so ought to do the job nicely.
 
#11
I recall Buzzford's GB but not the specific N channel part that was eventually chosen. (I didn't participate since I had bought some 19N20C and 12P20 when they were still available). Looking at the datasheets of 19N20C and 16N25C, the latter looks like a nice replacement for the former for our amplifier applications.

If Buzzforb's parts were matched by curve tracing then so much the better. Another thing I recall is that he took care to ensure the parts were geniune by procuring only those where provenance can be traced.

Good luck with your amplifier rebuild/repair.
 
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