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Old 15th April 2009, 08:22 AM   #1
Buhl is offline Buhl  Denmark
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Default Wtb: 2sk389-bl

I need at least one of these dual JFETs for my Pearl - if some one can spare a couple that would be absolutely fantastic!

Kind regards
Hans
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Old 6th May 2009, 05:23 PM   #2
JohanB is offline JohanB  Sweden
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Hi Hans,
I'm a newcomer to these pages and a little stupid about computers. Hope I can find the right buttons.....
Why do everybody want the BL & V type of the 2SK389? I have some new 2SK389-GR I can sell to you. I bought them myself in 1993 direct from Toshiba through Ericsson Components and have used many in my designs. When I heard Toshiba was ending production in the mid 90's I bought a big supply for the rainy days to come. So I still have many in my storage. I also have the 2SA1349-GR (PNP monolitic dual) and 2SK3381-GR (NPN monolitic dual) in large numbers. Sorry, no 2SJ109's.......

Johan
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Old 6th May 2009, 07:33 PM   #3
JohanB is offline JohanB  Sweden
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Hi again,
Sorry should be 2SC3381 (dual NPN) instead of 2SK3381.
As I see in other threads there are so many fakes and cheaters out there, I try to submit a couple of photos of the 2SK389-GR's. These J-FET's and transistors have been and still are in my possesion in all these years.

Johan
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Old 7th May 2009, 06:45 AM   #4
Buhl is offline Buhl  Denmark
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Default JFET grades

Tjänere Johan!
Thank you for you post and offer. I am not an expert on JFETs, but I will give it a try. The 2SK389 comes in three grades (GR, BL and V) for what I know. The difference in the grades is the Idss current - which is lowest in the GR and highest in the V - the BL in inbetween. What is also different (and more important for us who live in the cold part of the world and do not care about global warming) - is that the noise is lower in the high current part. This is very important in a Phono preamp - and I suspect that is the reason Wayne used this part in the Pearl. This is also the reason I requested the BL - it is what was used, and what I have used.

I have bought a pair of BL through Ebay (at a cost of about 100 Skr. for a pair!) - so I am no longer in need.

If I would be able to hear the difference in noise between the GR and the BL - I can not say - but it would be interesting if anyone have tried. The Pearl is exceptionally quiet though....

Kind regards
Hans
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Old 7th May 2009, 11:32 AM   #5
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Hi Johan,

I have just sent an email - let me know if you don't receive it.

thanks, sp
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Old 7th May 2009, 01:53 PM   #6
JohanB is offline JohanB  Sweden
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Default 2SK389-GR contra 2SK389-BL

Tjänare back Hans,

Yes you're rigth. There are 3 groups in Idss. GR (2,6 - 6,5mA), BL (6 - 12mA) & V (10-20mA). According to Toshiba´s data sheet there is absolutely no difference in noise performance between the 3 groups.
See http://pdf1.alldatasheet.com/datashe...BA/2SK389.html
I do understand some wants to use the V group, with the higher Vgs, when they have a complementary input where the source's are connected together by a resistor network and the gates are tied together.
But in ordinary differential input stages with constant current feeding I've not experienced any difference in noise between the 3 groups. As the Idss matching is made on Vgs = 0V in all groups, I prefer to run them on a lower Id, 1-3mA, closer to the data-sheet matching current, where these devices are intended to be used. Delta Vg1-Vg2 of max 20mV is measured @ 1mA in all groups. Yfs = 8-20@ 3mA also for all groups. Equavilent input noise voltage is also same and flattens out @ 2-3mA. These are some of the reasons I chose the GR-group for my designs.


Johan
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Old 7th May 2009, 03:35 PM   #7
h_a is offline h_a  Europe
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One can certainly use a GR in a LTP where the tail feeds 2mA (as in the Ono).

The 389 in the pearl runs at IDSS with degeneration, so the additional transconductance of BL and V-parts is good for additional gain (also higher signal-to-noise ratio as there is more gain) and higher negative feedback via the source resistor.

Wether that makes the world go round is a different story.

Have fun, Hannes
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Old 7th May 2009, 07:36 PM   #8
JohanB is offline JohanB  Sweden
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Default 2SK389-GR contra 2SK389-BL

Now this thread has derailed a little. Maybe there should be a new thread about this....Hm... But I must say here, that I can't follow h_a's thinking.
Toshiba specifies the same transconductance & equavilent input noise voltage (En) @ the same drain current (Id) for all 3 groups (compare in the data sheet in my earlier post). What differs is only the gate voltage Vg for that specified current. So gain and noise will be the same. As I wrote before, maybe some (the perl) need the extra Vg to keep up the desired current in the source resistor network...
I hope you don't mix up Idss with transconductance (Gm) & forward transfer admittance (Yfs).....


JohanB
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