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Old 13th June 2003, 10:02 PM   #1
RichardJones is offline RichardJones
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Default Help on Nemesis amp

On the schematic they have it looks like a bias point of 2.45volts. The current going to the OPT is 0.8 amps.

Looking at old datasheets for the 2SK135 this cannot be possible.

What is the actual bias and quiscent current for the amp???

Thanks.

p.s. I want to use the BUZ900P series instead.... what should I change?
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Old 13th June 2003, 10:07 PM   #2
RichardJones is offline RichardJones
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Default Datasheet

The datasheet is at:

http://www.bonavolta.ch/hobby/images.../2sk135j50.gif

Thanks!!!
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Old 16th June 2003, 06:11 AM   #3
djk is offline djk
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If you just look at the spec sheet the bias looks high.

But the RDS goes up from 1R0 to 1R7 over temperaure.

This is enough to require a higher gate voltage to keep the current in the ball park.

Running 30W through a 100W part is smokin' hot, I'll let you calculate the junction temperature.
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Old 16th June 2003, 02:35 PM   #4
RichardJones is offline RichardJones
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Default Its ok?

So the 2.4v bias will work then??? Looking at the spec sheet this looks way over 0.8A.

Is there something I am missing?

Oh and I have run 125W MOSFETS at 40W diss each with NO problem.

Anyone else have any suggestions?
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Old 18th June 2003, 06:08 PM   #5
RichardJones is offline RichardJones
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Default No more suggestions???

Come on.... there has to be someone else out there with suggestions about this circuit.

Planning on using 68,000uf of capacitance (or maybe 136Kuf) and battery supply.

Have some coupling caps... use Riken Ohm wherever I can.

EP OPT.

etc....

Can anyone explain the bias issue yet???

Thanks!
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Old 19th June 2003, 08:44 AM   #6
djk is offline djk
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You could make it with 'gasp', adjustable bias.

This is a 'who cares' thing.

Obsolete, expensive transistor. Hard-to-find, very expensive output transformer.
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Old 19th June 2003, 02:27 PM   #7
RichardJones is offline RichardJones
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Default hmm....

putting your smart *** comments aside....

I probably could do adjustable bias. The output tranny is not expensive... not as much as a good tube one.

The MOSFET can be easily replaced with a BUZ900 with just a small adjustment in bias.

Thanks anyway.
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Old 6th November 2003, 02:48 AM   #8
RichJones is offline RichJones  United States
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Default question

what is the purpose behind the resistor and cap across the primary of the opt? and the purpose of the resistor and cap from drain to gate?

Thanks!
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Old 6th November 2003, 03:36 AM   #9
Tube_Dude is offline Tube_Dude  Portugal
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Quote:
what is the purpose behind the resistor and cap across the primary of the opt?
Is a zobel network...for limiting the high frequencyes and making the primary of the tranformer look less inductif to the mos- fet.

Quote:
and the purpose of the resistor and cap from drain to gate?
Is to introduce some AC feedback and limit the distortion...that even so will be high...
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Old 6th November 2003, 10:11 PM   #10
RichJones is offline RichJones  United States
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Default values?

how do I determine the values??
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