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Old 10th April 2009, 09:02 AM   #1
housing is offline housing  Hong Kong
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Default Sony Vfet

I recently got a bunch of 2SJ18 and 2SK60, with V(p) of 52 and 51 respectively. Cosmetically they're nice showing no sign of remark. All of them tested fine according to Sony's service manual except one piece of 2SJ18. I popped it open with a hacksaw aided by a vice and luckily there ain't any diode or 1R resistors inside but a die of about 3mm+ square.

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I understand that these Vfets may not be used to repair some Sony amp models because of their lower V(p). I'm asking for members assistance to see whether there's any circuit for testing the exact V(p) of each Vfet as well as suitably designed Vfet DIY amp circuits floating around. Please don't ask me to google as I can't find any except a couple of Japanese circuits that I don't understand. Thanks.

Below are the images showing how I test a piece of 2SJ18.

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Old 10th April 2009, 09:56 AM   #2
EUVL is offline EUVL  Europe
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Disclaimer: have not done this myself with Sony VFETs before, so test at your own risk.

If by Vp you mean pinch voltage, then this is the Vgs at which the drain current Id is zero.

Since these are high current devices, you can test the Vp approximately by feeding the drain from a power supply (say 10V) via a 1mA constant current source. The voltage measured across gate-source would approximate Vp.

Another way is to connect drain of N-device (2SK60) to +10V, source to a 100k resistor, the other end of which then to ground, gate also to ground (optionally via a 100R resistor). The voltage across Vgs would also be very close to pitch voltage, and the device is safe, as maximum possble current through the device is 10V/100k = 0.1mA

Strongly advise you test the procedure first with a more-available power JFET (e.g. LU1014).


Patrick

PS As to circuits, you already knew the Japanese sites; and if you don't want to build any of those, I also cannot help you. Maybe a search here at DIYA under 2SK60 will yield something.

http://www.diyaudio.com/forums/showt...304#post213304



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Old 11th April 2009, 10:12 AM   #3
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i have the ta-8650 cct if your feeling brave, problem as you have shown is they are normally 'on' fets, tricky stopping them conducting when power is initially applied
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Old 11th April 2009, 12:14 PM   #4
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a pic of fets in a 8650 thay look similar to the ones you have
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Old 8th January 2013, 11:03 PM   #5
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Default Possible VFE output configurations

From Sony AES preprints:
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Old 8th January 2013, 11:06 PM   #6
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Default VFET driver

From Sony AES preprint again.
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Old 8th January 2013, 11:14 PM   #7
Zen Mod is offline Zen Mod  Serbia
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have complete article ?

co-incidentally - I'm doing complete re-vamp of one TA-5650 , these days
hopefully - it will sing tomorrow
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Old 8th January 2013, 11:17 PM   #8
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Yes I have. And I also think I might have your email address somewhere as well.


/RK
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Old 8th January 2013, 11:19 PM   #9
Zen Mod is offline Zen Mod  Serbia
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should I rehash it , and put somewhere for down ....... or we'll behave ?

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Old 8th January 2013, 11:21 PM   #10
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I don't know. It is ancient - will anyone care? But it is AES property. I think.
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