Hi Mike,
I have matched a few batches. Hard to get a good solid number on this subject. Often, I will get sequences of 4 to 5 fets in a row (in order from tube) that match great. Then, the next one will be different by 200 mV.
With 50 fets, I usually get 5 or 6 good sets of 6.
With 100 fets, I can get usually get 15 good sets.
Sometimes less, never more. 40 may get you your sets.
Dale
I have matched a few batches. Hard to get a good solid number on this subject. Often, I will get sequences of 4 to 5 fets in a row (in order from tube) that match great. Then, the next one will be different by 200 mV.
With 50 fets, I usually get 5 or 6 good sets of 6.
With 100 fets, I can get usually get 15 good sets.
Sometimes less, never more. 40 may get you your sets.
Dale
That's a difficult question to answer. I used IRF644s (TO-220 case device) when I built my Aleph 2s. I wasn't sure what to do, so I ordered 100 in order to get the price break. Good thing I did. Out of a batch of 100, I had a nearly impossible job to find decently matched sets. It was a nightmare. The other side of the coin was when I ordered IRFP044s for the Aleph-X prototype. I got 20 and was able to get four pairs of nearly perfectly matched devices. The rest were close enough that I wouldn't be ashamed to use them.
I'd say to plan on ordering at least 50% more devices than you need and hope that you have better luck than I did with the '644s.
Grey
I'd say to plan on ordering at least 50% more devices than you need and hope that you have better luck than I did with the '644s.
Grey
Building an Aleph4 I ordered 40 IRFP240 and I was able to make 5 groups of 6 close matched. For A4 one only needs to have 4 different groups.
The supplier for the IRFP240 was D-K who sent all from the same lot and was an easy job.
I was able to match: (groups of 6)
1.- within 0.01V
2.- 0.03V
3.- 0.03V
4.- 0.04V
5.- 0.04V
Total spread from all 5 groups was 0.27V (highest 4.42 - lowest 4.15)
Used 13.57V supply for matching with a 10 Ohm resistor for 20 Sec.
I guess that for AX one needs to have the upper (CCS) and lower (active) 2 set matched. So two sets in total to match for each amp.
Since I haven't built an AX I can't say, but I'm sure that many other members can guide on how many sets you need to match for each amp.
P.S. Uuups sorry, you are buiding an A2 so please ignore my coments on AX.
The supplier for the IRFP240 was D-K who sent all from the same lot and was an easy job.
I was able to match: (groups of 6)
1.- within 0.01V
2.- 0.03V
3.- 0.03V
4.- 0.04V
5.- 0.04V
Total spread from all 5 groups was 0.27V (highest 4.42 - lowest 4.15)
Used 13.57V supply for matching with a 10 Ohm resistor for 20 Sec.
I guess that for AX one needs to have the upper (CCS) and lower (active) 2 set matched. So two sets in total to match for each amp.
Since I haven't built an AX I can't say, but I'm sure that many other members can guide on how many sets you need to match for each amp.
P.S. Uuups sorry, you are buiding an A2 so please ignore my coments on AX.
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