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housing 10th April 2009 09:02 AM

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. :D :D :D

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.

EUVL 10th April 2009 09:56 AM

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).


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.

bosedtobosed 11th April 2009 10:12 AM

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

bosedtobosed 11th April 2009 12:14 PM

2 Attachment(s)
a pic of fets in a 8650 thay look similar to the ones you have

R-K Rønningstad 8th January 2013 11:03 PM

Possible VFE output configurations
1 Attachment(s)
From Sony AES preprints:

R-K Rønningstad 8th January 2013 11:06 PM

VFET driver
1 Attachment(s)
From Sony AES preprint again.

Zen Mod 8th January 2013 11:14 PM

have complete article ?

co-incidentally - I'm doing complete re-vamp of one TA-5650 , these days
hopefully - it will sing tomorrow

R-K Rønningstad 8th January 2013 11:17 PM

Yes I have. And I also think I might have your email address :eek: somewhere as well.


Zen Mod 8th January 2013 11:19 PM


should I rehash it , and put somewhere for down ....... or we'll behave ?


R-K Rønningstad 8th January 2013 11:21 PM

I don't know. It is ancient - will anyone care? But it is AES property. I think.:confused:

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