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Old 3rd July 2002, 02:38 PM   #1
exurbia is offline exurbia  Australia
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Smile I need help class a please

I have searched the forums for a class A bipolar, not single ended ampli. I need 60-80 watts heatsinking is no problem.
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Old 3rd July 2002, 05:43 PM   #2
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Default Is this close enough?

http://www.passdiy.com/pdf/A75p1.pdf
http://www.passdiy.com/pdf/A75p2.pdf
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Old 3rd July 2002, 06:24 PM   #3
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Smile class A bipolar

Probably not...... by Bipolar I would think he meant NPNs and PNPs.

H.H.
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Old 3rd July 2002, 06:39 PM   #4
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I know Harry, that's why I said <i>close enough</i>. Anyway, sand is sand. Besides I didn't know how attached exurbia was to the idea of mosfets or transistors as against a good complementary topology. Gotta ask, eh?
It was a start at least and with a proven design in the right power range. Almost all the bipolar class A amps above a few watts I've seen have thermal stability problems of some kind and a tendency to self destruct. I'm sure there are examples that don't but.....
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Old 3rd July 2002, 08:36 PM   #5
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Really, Bipolar reliability should not be an issue for this
sort of thing. You only have to watch out for second
breakdown and place some emitter resistance on each
output device. In fact, I find a reasonably designed
bipolar Class A to be more stable thermally than an AB
because substantial DC voltage appears across the
emitter resistors, and the shifting Vbe is a lesser percentage
of this figure.
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Old 3rd July 2002, 09:06 PM   #6
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For bipolar class A designs Geoff's fantastic site will be the best I suppose

http://www.gmweb.btinternet.co.uk/

Ergo
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Old 4th July 2002, 03:48 AM   #7
exurbia is offline exurbia  Australia
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thanks' for comments, I wanted a bipolar design as i have a huge amount of mj15003/4 . It would be nice to use them up also got tip 35/6. can these be of any use.
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Old 4th July 2002, 04:01 AM   #8
exurbia is offline exurbia  Australia
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just looked at ref site can anyone offer comments on stan curtis a60? would i be better off using a new front end ala randy slone cascode. would this be better?. how about building a 300 watter and derating the supply rails and increasing bias. normally i build kits now i would like to try my hand at something i can modify. my heatsinks can dissipate 3kw for @25 with 30 deg rise, they are made from engine doors, any marine or power station fitters will know what they are
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Old 4th July 2002, 05:00 AM   #9
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with many mj15003 you could built a big big class a amp. go to geoff site, he puts up the JLH amp for 10, 15 watts. Increase the rail supply higher from 20 volts to maybe 40 -50 volts with increase in Iq too and get yourself a 60-80watts of class A power. USe many mj15003 as each device takes a maximum of 250 watts(temperature brings down the maximum power for the transistor and also used a safety factor). Maybe Geoff can put you on the write track, email him.
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