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AndrewT 20th October 2004 07:56 PM

2SJ81 & 2sK255 help identify
I have a Sugden P128 monoblock power amp.
The output pair are 2 off each 2sj81 Pch and 2sk255 Nch. They are flat pack 2 bolt fixing.
I cannot find any data. Can anyone point me to a site?
ps. the reason I ask is; my other pair have had the mosfets replaced, before I bought them, with 2sj200 and 2sk1529 & I cannot adjust the Iq high enough with the result they run cold @ about 16mA.
Andrew T.

Netlist 20th October 2004 08:08 PM

Here is something:

2SJ81: V-MOS, 120V, 7A, 100W, <1,7ohm,230/110ns
2SK225: V-MOS, 120V, 7A, 100W, <1,7ohm,180/60ns


PMik 20th October 2004 09:42 PM

Use 2SJ162/2SK1058 as close an eqv. for 2SJ81/82/83 and 2SK225/226/227 you can get.
but comes in TO-3P Housing, so you have to drill some new holes ;)

AndrewT 21st October 2004 06:16 PM

Hi all,
thanks for comments so far.
I am surprised that 2sj81 is rated at 120v 7a 100w.
the amp is running on +71v & -71v power rails and +-80.5v driver rails. I think it is designed to produce about 180w- 200w into 8r.
Two of those mosfets in parallel would seem under designed. Maybe that's why the other amp has been repaired.
The partners are 2sk255 NOT as replies earlier.
Does this mean they are not true pairs?

Netlist 21st October 2004 06:48 PM

2 Attachment(s)
Hi Andrew,
There's no 2SK255 in my book(s).
The 2SK225 is definitely the complementary type.
Have attached some more info on the 2SJ81.

The 2Sk200 and 2SJ1529 are pairs.
2SJ200: V-MOS, NF-E, 180V, 10A, 120W
2SK1529: V-MOS, NF-E, 180V, 10A, 120W

You can find datasheets with google for these.

/Hugo :)

AndrewT 24th October 2004 09:55 PM

Thanks all,
Netlist, reading your data page (a bit small but I just managed) I could compare 2sj81 with 2sj162 & found their Vgs is between 0.45v and 1.45v. BUT 2sj200 has a Vgs range of 0.8v to 2.8v. This explains why I cannot adjust Iq upto a sensible value.
My choice now is to swap the SJ200/k1529 for the new alternative or change the resistive bias pot to a Vbe multiplier connected to the output heatsink. Seems simple now.
Thanks again
Andrew T.

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