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. 
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.
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.
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/showthread.php?postid=213304#post213304
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/showthread.php?postid=213304#post213304
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