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Old 16th April 2005, 11:26 AM   #1
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Default Hitachi FET Substitution

Hi,


I am thinking about building an AEM6000 (or 6) which uses Hitachi 2sk176/2SJ56
The Hitachiís are obsolete and it has been suggested I replace them with Exicon EC10N20/EC10P20.

This raises a few questions,
So I'm hoping someone out there can impart a little wisdom with regard to Mosfet substitution.


Is the replacement of the Hitachiís with the Exicon's a straight forward substitution?

Ignoring the basics Ė IE power ratings (feel free to point out they are an issue)

I see that many of the specs listed in the data sheets have not been measured under the same test conditions,
Making it difficult for a direct comparison (for yours truly with minimal understanding).

There are also many small variations - input/output capacitance turn on/turn off time (and possibly more bit's I've missed?)


What should the substitution newbie be looking for, when evaluating options?
Which parameters will have the greatest effect on the performance and stability of the amplifier?

If I use Exicon's in the AEM6000
Do I need to change the value of the source gate capacitor for the n channel devices?
Or any of the source gate RC network on the p's?
or any of the other bits I don't understand?
(Yeh, if you were wondering I did try to come to grips with the original cct description - try is the important word here)

The AEM6000 output schematic is lurking in another post

http://www.diyaudio.com/forums/attac...amp=1056171351



There have been a number of posts which relate to specific device substitution.
Can those of us with a limited (read none) understanding of electronics apply any rules of thumb when contemplating this type of power FET replacement?

Given any power amplifier
Assume it has a reasonable well designed/stable output stage and was designed for obsolete Hitachi pairs, 2sk176/2sj56 2sk134/2sj49 etc
Can the similarly rated Exicons be used as direct replacements?
Should changes be made anywhere to maintain stability?


How will the Exicon equivalents affect the measured performance, distortion levels, Slew rate etc?
Can these changes be predicted?
Or are changes in these parameters likely to be CCT or bias specific?


Going back to the AEM6000, can I predict/expect a change in the published specs?

Appreciate your thoughts

Thanks
Tony
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Old 16th April 2005, 03:25 PM   #2
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There are at least two companies or manufacturers distributing or making what was Hitachi Power Mosfets today. They may be broken down by geographic region (seems to be the case). My understanding is that at least *one* of them merely inherited the original Hitachi production line intact. The other I believe is licensed. I think that is what is going on...

At least in the USA, it doesn't seem that easy to find and acquire these parts - at least not at a good price, assuming the big distributors have them or can get them...

But, the answer to your question is that if the specs are the same, the part is the same. I've noticed some "newer" parts which are either higher power, higher voltage or both which have been added to their product range...

It's not my aim to disuade you from building something, but the circuit you showed isn't one that I would personally want to build. For one thing those caps on the Mosfets are too large, imho. Which indicates to me that the amp is marginally stable, and is likely to have fairly poor bandwidth as it stands...

Perhaps you might want to look at some other driver boards and designs... I like the offerings from Erno Borbely for one. http://www.borbelyaudio.com



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Old 16th April 2005, 03:52 PM   #3
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The Exicon parts are a straight replacement no changes to anything required.
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Old 16th April 2005, 05:40 PM   #4
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Default Renesas....................

Hitachi and Mitsubishi joined up their semicon divisions according to what I see on the web. They are now Renesas.
Their production line is functioning again and the 2SK1058/J162 and their higher voltage versions 2SK2220(21) /2SJ351(2) (?) and 2SK213.....216/2SJ76...79 are mentioned on their web page.
So it must be just a matter of time before we can get these parts easily ,again.
Cheers,
Ashok.
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Old 20th April 2005, 07:50 AM   #5
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Guys,

Thanks for your comments/suggestions

looks like I have much to think about........................

Appreciate your help

regards
Tony
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Old 17th May 2005, 10:52 AM   #6
Koryusz is offline Koryusz  Hong Kong
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Hi,

I still have Hitachi MOSFET 2SK135/2SJ50. Let me if you need them.
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Old 18th May 2005, 03:35 AM   #7
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I own two Soundcraftsmen amps. The PCR 800 uses Hitachi MOSFETs and the S 860 uses the Exicons. I think the S860 sounds better.

Blessings, Terry
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Old 18th May 2005, 05:21 AM   #8
Koryusz is offline Koryusz  Hong Kong
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Well.. for me. I like Hitachi. It has the warm nature as tube. That's why I keeping using them for many years.
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Old 18th May 2005, 06:24 AM   #9
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Quote:
I think the S860 sounds better
The difference in sound need not be due to the power transistors alone unless the rest of the circuitry , construction and parts type are absolutely identical.
Are the two amps identical in every other way ?
Cheers.
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Old 18th May 2005, 08:11 AM   #10
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Exactly ashok! Some objective comparisons would be of value here. My nested feedback amplifier designs render the sound effectively independent of output device character - lateral or vertical MOSFET or even BJT, they only deliver without colour.

Then it's down to reliability/power delivery/PS efficiency.
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