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Old 13th March 2004, 04:56 PM   #11
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Originally posted by Charles Hansen
Per Anders is right. Use a Vbe multiplier as I suggested above, and mount it on the heatsinks. To address the bias stability of the input transistor as Traderbam noted, add an emitter resistor on the input transistor.
A Mosfet Vgs multiplier would be even more appropriate, and
consider some small output Source resistors, like .33 - .47 ohm.

Then, I think you'll have an amp.
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Old 19th March 2004, 03:09 AM   #12
Diode is offline Diode  United States
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This one's pretty simple but FET's aren't made any more. Check with the FET experts to convert it to IRF FET's. If nothing more, you may get some ideas about biasing.

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Old 19th March 2004, 11:22 PM   #13
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Hello Diode,

I wouldn't try to put vertical FETs in an amp designed for lateral FETs. The lateral FETs are still made. Hitachi split off their semiconductor division as Renesas. You can see their products at:

Click on the link that says "Power MOSFET for General Amplifier". They don't make metal TO-3 packages any more, but they do make the plastic TO-3P (TO-247) packages.

Improved clones are also made in England by Magnatec:

These are available in both plastic and metal packages.

Hope this helps,
Charles Hansen
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Old 19th March 2004, 11:58 PM   #14
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Do you know of a Renasas distributor in the U.S.?

Ugh... I'm sorry, I just answered my own question. It looks like Arrow stocks them. $5 for 2SK1058's is pretty remarkable considering what some folks are selling NOS for.

Well, since I have you on the line...

I was reading your Balun article (Thanks!) I'd like to add some attenuation at the input of the receiver for speaker-level inputs (bal/unbal) for a distortion measuring rig. Do you know of any pitfalls in using dividers with these chips?
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Old 20th March 2004, 01:21 AM   #15
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Believe it or not, there are two Charles Hansens in audio. I work for Ayre Acoustics and live in Colorado, and the other Charles Hansen lives back east and writes articles for AudioXpress. It's kind of confusing....
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Old 20th March 2004, 02:30 AM   #16
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Sorry for my gaff, Charles. But thanks nonetheless!

So you're the Ayre guy.... Cool
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