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Old 6th May 2009, 02:01 AM   #21
diyAudio Member
 
Join Date: May 2008
hello All

Finding matched 2SJ74 at a logic price has been impossible and buying enough of a pool for matching myself to expensive

Since I have these 2SK170s Can these be used

Cheers
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Old 6th May 2009, 04:39 PM   #22
gl is offline gl  United States
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Join Date: Dec 2003
Location: Sierra Foothills - California
Welllllll...yes. But not without journeying into some new territory.

You'll need to flip the whole circuit over so to speak, swapping positive with negative and substituting P devices for N devices and vice versa. I personally don't see any major issues. The transconductance shelving thing may be a small issue if you use the IR 9240 in the Aleph CCS circuit. The transconductance of the transistors here are a term in the currant gain equation.

It seems like a lot of trouble to go through because the available 2SJ74's are considered too expensive. Prices I have seen lately are in the $1.50 - $2.00 US each range IIRC. That's not too expensive IMO.

Cheers,
Graeme
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Old 6th May 2009, 06:12 PM   #23
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Join Date: Jul 2005
Location: East Sussex
Hi Dan
Presently on EBay:-
30 P-Channel Silicon Transistor 2SJ74 J74 Low Noise BL
EQ or MC amplifier Vgds=-40V Id=-20mA,Pd=400mW BL Grade Item number: 130299423489
Price for these is $30.30 inc shipping, so approx $1 each

How do you fancy going halves after matching? PM me.
Regards.
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Old 6th May 2009, 10:56 PM   #24
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Join Date: May 2008
Hello Grame

How big a pool does one require to get a excellent matching result?

with my pool of 40 2SK170 I only received a few closely matched pairs.
Cheers

With two monos and double JFET diff pair, thats two lots of four closely matched, how does a pool of 60 sound?
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Old 6th May 2009, 11:32 PM   #25
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
Hi Dan,

Although I own a stash of 2SK170's and 2SJ74's I've not yet had the need to measure and match these parts. So my answer is: I don't know.

Others on this web site have matched these parts and reported their results. Hopefully one or more will respond here. IIRC their results correlate well with what you found with the 2SK170's. I have found that as the number of parts in the sample rises the percentage of close matches also rises.

Graeme
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