switching power supply.. can't get -24v?

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#82
Well I talekd to seller of the boards and he writes:

Please see below.. is it possible these are fake J109 by the readings of open on the pins 2-3 and 5-6?

-------- Original Message -------- Subject: Re: Emailing: SAM_1738Date: Tue, 21 Feb 2012 15:22:55 +0800From: Stanton Tin <stantontin@gmail.com>To: Bscorner

Dear sir,


I do not think your power supply blown the JFETs.


The JFETs may be faked.


Maybe I should tell you a fact. 99.9% of these twin FETs are fake. Toshiba has ended the production of 2SJ109BL over 10 years ago. They cannot be sold at this price. Neither could they be so abundant in the market. You may send a message to Pass Lab. I think they have swept all the old stock parts from the world. Most of these fake parts selling in ebay were fake from twin BJT, and obviously, BJT has no Idss.


I knew this because I was also a sufferer of these fake parts.


I suggest you to use two matched 2SJ74BL instead. 2SJ74BL can still be obtained from the market readily.


Best Regards,
JIMS AUDIO



On Tue, Feb 21, 2012 at 6:14 PM, BsCorner wrote:
On 2/20/2012 10:48 PM, Stanton Tin wrote:
Idss cannot be adjusted. It is an inherent parameter of the chip.

In first place it must be a genuine JFET. Otherwise there is no Idss.


I attached a diagram. You can follow to check the component. Firstly the two measurement reading should be the same. Secondly the reading should be a low ohm, like 100 ohm or below. If you get kilohm order then it is not right.
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Ok I did the test but i read OPEN! i think maybe jfet was damaged when psu was hooked up wrong?

I retested the pins shown and get only open on both tests.

Now i must order new jfets? i would like to use more common part.
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#83
if the sj109's ae from ebay, they are fake. i know one company thet have the real deal. but they cost over 30£ pr. pc.
so matched sj74 are the best way. contact FETstore.com.
also siliconray has them. i do not belive he is selling fake parts🙂
 
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#84
Genuine 2SJ109 are basically unobtanium anymore...

As the vendor suggested, use a matched pair (per channel) of 2SJ74. Genuine ones are still available from honest dealers, look at AMB audio shop or a member named "Blues" on this forum. There are a couple of other guys on the forum who sell genuine ones, but their names escape me right now.

Also, in case you didn't know, the 2SJ109 is just a pair of 2SJ74's in a common case. There is no downside to using the J74's. Make sure you install them correctly.
 
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#85
6L6 said:
Genuine 2SJ109 are basically unobtanium anymore...

As the vendor suggested, use a matched pair (per channel) of 2SJ74. Genuine ones are still available from honest dealers, look at AMB audio shop or a member named "Blues" on this forum. There are a couple of other guys on the forum who sell genuine ones, but their names escape me right now.

Also, in case you didn't know, the 2SJ109 is just a pair of 2SJ74's in a common case. There is no downside to using the J74's. Make sure you install them correctly.
Click to expand...

the do need to be mounted back to back with thermalgreese. (for best performence) and striped togheter.
 
#91
Zen Mod said:
wrong polarity , Bubba .

you need pair of 2SJ74BL

but - most important - you need either to little more learn basic electronic , or little more learn how to build strictly by the book ( if not in the mood for learning electronic)
Click to expand...

Efff -- are you serious.. i got a matched pair of 2SJ74 in the datasheet photocopy under the lettering it also says 2SK170. Same fet?!

the writing on the fets is K170.
 
#97
Do you have the voltages over R7 and R8 mentioned in the scheme?

95797d1194037871-aleph-j-schematic-aleph_j_sch.pdf



There can be different reasons......
Are your J74 a bit matched on Idss?

If you replace R7 by a pot of 1kOhm it might be possible to adjust the offset.
 
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