Unfortunately, the 2SK170 and 2SJ74 are on their way out, too. I remember speculating about that six months ago and now it seems to have happened. Toshiba no longer lists any low noise P-ch devices at all and only one "general purpose" complementary pair of single JFETs. Toshiba distribution being what it is here in the US, those are not easy to locate, either. And there's still the age-old problem of not being able to control the grade of device you're buying. The JFET availability situation grows worse daily; nay...hourly.
John Curl seems to have reservations about the Linear Systems devices, but I don't have the array of test gear that he and Nelson can bring to bear on the matter. To me they seem to work okay.
The bottom line is that you don't have a choice. With the Toshiba parts nearly impossible to get and very, very expensive, Linear Systems is pretty much the only game in town at this time.
This is one of the reasons I have not posted a circuit in a while. I've been using JFETs for small signal applications (low level and amplifier front ends) for a couple of years now, but there's no point in posting circuits that few can build.
Arguably, I could re-jigger at least some of the circuits to use, say, the smaller Zetex MOSFETs, but my time is horribly limited at the moment and I can't justify running two side-by-side projects, one with JFETs and another with MOSFETs, in order to please everyone. Nor can I justify stocking parts that I won't be using for anything other than projects to post. Especially since I just took a bit of a financial hit and parts cost money. Going to have to watch my spending for a while.
Bummer.
Grey
John Curl seems to have reservations about the Linear Systems devices, but I don't have the array of test gear that he and Nelson can bring to bear on the matter. To me they seem to work okay.
The bottom line is that you don't have a choice. With the Toshiba parts nearly impossible to get and very, very expensive, Linear Systems is pretty much the only game in town at this time.
This is one of the reasons I have not posted a circuit in a while. I've been using JFETs for small signal applications (low level and amplifier front ends) for a couple of years now, but there's no point in posting circuits that few can build.
Arguably, I could re-jigger at least some of the circuits to use, say, the smaller Zetex MOSFETs, but my time is horribly limited at the moment and I can't justify running two side-by-side projects, one with JFETs and another with MOSFETs, in order to please everyone. Nor can I justify stocking parts that I won't be using for anything other than projects to post. Especially since I just took a bit of a financial hit and parts cost money. Going to have to watch my spending for a while.
Bummer.
Grey
Which muddies the waters considerably...
The other night I was on the Toshiba web site and brought up a PDF catalog of "all" of their semiconductors. That's where I got my information. However, I've got their site going in another tab and went down another train of links and the following page:
http://www.semicon.toshiba.co.jp/eng/product/transistor/selection/mos/fet/lead.html
has links to the 2SJ108 and the 2SJ74 datasheets. As to their actual availability, that's another question.
The datasheet for the 2SK370 shows a date of 3/26/03.
Ah, ha! Found it!
The main transistor catalog:
http://www.semicon.toshiba.co.jp/docs/catalog/en/SCE0004-08_catalog.pdf
dated August of this year, shows no low noise P-ch JFETs at all (the 2SK370 is listed, but the 2SJ108 is not) and only the general purpose 2SK246/2SJ103 (TO-92) and 2SK330/2SJ105 ("Mini") available as complements.
I am assuming--perhaps in error--that an August '07 catalog trumps a March '03 datasheet in terms of what is current.
They do still have the 2SJ74 datasheet available, but the 2SK389 and 2SJ109 datasheets are gone. I seem to recall that they were still available as of this past spring.
Incidentally, they do show a couple of N-ch surface mount duals, but no P-ch complements.
Granted, there are days when I could teach Eeyore a thing or two about pessimism, but to me it seems that the tide is against us.
Grey
The other night I was on the Toshiba web site and brought up a PDF catalog of "all" of their semiconductors. That's where I got my information. However, I've got their site going in another tab and went down another train of links and the following page:
http://www.semicon.toshiba.co.jp/eng/product/transistor/selection/mos/fet/lead.html
has links to the 2SJ108 and the 2SJ74 datasheets. As to their actual availability, that's another question.
The datasheet for the 2SK370 shows a date of 3/26/03.
Ah, ha! Found it!
The main transistor catalog:
http://www.semicon.toshiba.co.jp/docs/catalog/en/SCE0004-08_catalog.pdf
dated August of this year, shows no low noise P-ch JFETs at all (the 2SK370 is listed, but the 2SJ108 is not) and only the general purpose 2SK246/2SJ103 (TO-92) and 2SK330/2SJ105 ("Mini") available as complements.
I am assuming--perhaps in error--that an August '07 catalog trumps a March '03 datasheet in terms of what is current.
They do still have the 2SJ74 datasheet available, but the 2SK389 and 2SJ109 datasheets are gone. I seem to recall that they were still available as of this past spring.
Incidentally, they do show a couple of N-ch surface mount duals, but no P-ch complements.
Granted, there are days when I could teach Eeyore a thing or two about pessimism, but to me it seems that the tide is against us.
Grey
Very Good JFET info here guys, thanks.
If I may ask, since I am new to the layout/design; Mr. Rollins, in your A-X design, what are suitable values for R2/R3/R42/R43 and for R1/R4/R44/R45? I have seen designs that use a single 100ohm in the R1/R4/R44/R45 spot, will this work? For the other spot (R2/R3/R42/R43) does this have to be the same value as the source resistor? Can any of these be omitted at all, or should they all be included? Also in the R2/R3/R42/R43 spot do you have to add more of these as the power output increases? Lastly are wire wounds preferred here or can you use precision thick films rated for like 30watts or so?
EDIT: Never mind...most questions where answered in the Wiki!!!
But it still stands, can I use thick films here or should I stick to wire wounds?
Also can I use ZTX450's instead of the MPSA18?
If I may ask, since I am new to the layout/design; Mr. Rollins, in your A-X design, what are suitable values for R2/R3/R42/R43 and for R1/R4/R44/R45? I have seen designs that use a single 100ohm in the R1/R4/R44/R45 spot, will this work? For the other spot (R2/R3/R42/R43) does this have to be the same value as the source resistor? Can any of these be omitted at all, or should they all be included? Also in the R2/R3/R42/R43 spot do you have to add more of these as the power output increases? Lastly are wire wounds preferred here or can you use precision thick films rated for like 30watts or so?
EDIT: Never mind...most questions where answered in the Wiki!!!
But it still stands, can I use thick films here or should I stick to wire wounds?
Also can I use ZTX450's instead of the MPSA18?
The answers to most every question in the universe--including, I think, "42"--are available in the Aleph-X thread. However, it seems that many people are intimidated by the number of pages.
As for what I regard as suitable values for resistors, you can check the schematic...those are what I regard as suitable values. If you start scaling the circuit up or down, then you'll have to think about where you want to go before trying to decide how to get there.
People have used most every kind of resistor known to man in building Aleph-Xs. As I said in the Aleph-X thread, I lean towards metal film resistors.
The MPSA18 substitution question was also covered in the Aleph-X thread, but yes, the ZTX450 is fine.
Grey
As for what I regard as suitable values for resistors, you can check the schematic...those are what I regard as suitable values. If you start scaling the circuit up or down, then you'll have to think about where you want to go before trying to decide how to get there.
People have used most every kind of resistor known to man in building Aleph-Xs. As I said in the Aleph-X thread, I lean towards metal film resistors.
The MPSA18 substitution question was also covered in the Aleph-X thread, but yes, the ZTX450 is fine.
Grey
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