NEED 2SK225 & 2SJ81 FETs for Sugden amp! Help! - diyAudio
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Old 25th April 2008, 07:36 AM   #1
milosz is offline milosz  United States
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Default NEED 2SK225 & 2SJ81 FETs for Sugden amp! Help!

I NEED 2SK225 & 2SJ81 FETs for a recently dead channel in my dear old Sugden A25 amp-

These old Hitachi FETs are obsolete- and I cannot find a cross to them.

Can anyone offer a suggestion of a replacement pair?

And, if I replace the dead channel's pair, do I also need to replace the other channel's FETs to keep both left and right sounding the same?
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Old 25th April 2008, 02:59 PM   #2
burbeck is offline burbeck  United Kingdom
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hi try, 2sj162 and 2sk1058

these parts are single hole fixing, so you may have to drill new mounting holes.

also i think that the pin outs are the same, but please check this

the Iq will need reseting on the amp.
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Old 26th April 2008, 08:45 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
does the A25 have a single pair or a two pair output stage?
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Old 26th April 2008, 10:04 AM   #4
Mooly is offline Mooly  United Kingdom
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Hi, Can you first of all confirm what package they are. T03, or flat pack. By the way, have you tried E-Mailing Sugden to ask what they recommend. They are a very friendly bunch, and I had the good fortune of a tour of the factory a couple of years back. Worth a try ? Back to the FET's, there was a similar thread a while back and I made the mistake of assuming the 2SJ/K type were like the laterals we know today, when in fact they are not. Some of the very early FETS have very different transconductance characteristics and the pinch off voltage is significantly different, they are not directly equivalent with the modern types.
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Old 26th April 2008, 10:44 AM   #5
AndrewT is offline AndrewT  Scotland
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The 2sj81/k225 are Lateral FETs in MT200 package (two hole flatpack).
The equivalent in To247 package is the 2sj160/k1056, but the higher voltage versions will work just as well, i.e. 2sj161/k1057 or 2sj162/k1058.
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Old 23rd May 2008, 09:59 PM   #6
aandy is offline aandy  United Kingdom
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best use 2sk2221 and 2sj352,as they are more stable than the 1058/162
recent batches of the 2sj162 2sk1058 are a bit trying to say the least.
the bius will not need to be changed with these fets
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Old 11th September 2013, 07:24 AM   #7
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Great success with BUZ901P and 906P.
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Old 11th September 2013, 07:55 AM   #8
milosz is offline milosz  United States
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Default Not bad after all

I eventually found exact replacements, some old stock that was in some dusty old box....

Thanks for all the suggestions.

By the way, Sugden kindly supplied a schematic for this amp, and I post it here for reference by anyone needing it.

Click the image to open in full size.
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Old 11th September 2013, 02:17 PM   #9
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The classic Hitachi lateral circuit yet again
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Old 13th September 2013, 09:50 AM   #10
AndrewT is offline AndrewT  Scotland
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Notice how Sugden have shown the local decoupling C9 & 10. Quite separate from the supply rail decoupling C11 & 12.

Can you see where C15 & 20 are located relative to the opamps?
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