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Old 2nd January 2004, 02:17 AM   #1
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Question PSU cap voltages

Hi guys,

I need some help with the power supply below. I plan to build the power suppy but I dont know what voltage or size capacitors to buy for the 4 right hand side capacitors.
Can anyone suggest some values?
In case it helps I have also added the amp that the power supply is for.


Thanks in advance
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Old 2nd January 2004, 04:52 AM   #2
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I'm not a guru, so take advice with a grain of salt.
The top and bottom must be at least 60v the middle 2 must be at least 30v. These are working volts, not surge. I would go with at least 75v and 50v.
As for capacitance, The outside 2 that supply the valves likely don't supply much current, so I would think that 1000 uf would do but the more you have the less supply ripple you have. These may sound better with bypass caps. (high grade "fast" caps of about 1-5 uf). The inside pair that supply your output fets depend a little on your bias current. you should be able to swing near 30v+- Which is about 4A at 8@. I would shoot for more than 10,000 uf so you have plenty of current reserves. And definatly use bypass caps here if the bias is under 3A.
The four on the left need to be 1-5 times the cap of the outside pair. I don't fully understand if the voltage multiplier will work or what voltage these caps will see.
Good luck with it. The resistor between the gates that I think sets the bias may be a bit low. I would guess that you need to see 7-9 volts between the gates or you'll have a lot of crossover distortion. But I'm far from an EE, so if you trust the source of the circuit, give it a try. let us know how it works.
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Old 2nd January 2004, 08:49 AM   #3
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The caps on the right hand side take it in the shorts. I would use 100F 150V and wire a 10 ohm 1/2W resistor in series with each one.

I see no point in using expensive 250V parts either. Dump the Magnetech BUZ901/906 and go for Exicon 10N160/10P160 for half the money.

Bias looks OK for Lateral MOS.

You going to run any feedback?

You do know you need a duplicate supply for each channel?
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Old 2nd January 2004, 06:30 PM   #4
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Hi guys thanks for the replies.

djk, why should I put the 10 ohm 1/2W resistor in series with capacitors, how would it help?
I already have the Magnetech mosfets (the double die versions) thats why I chose to buid this amp. If there are any more simple amps that you know that these mosfet will work in let me know.

The amp already has feedback, the power supply configuration forms the feedback, you can find the explanation here: http://www.tubecad.com/index_files/page0025.htm


I have one more question for you guys. For the diodes in the amp would 1N4148 be fine, and for the zeners would a 9 volt work?



Thanks again
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Old 3rd January 2004, 12:37 PM   #5
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Why don't you build something that will work?

http://www.homestead.com/whaan/files/page6463.html

The schematics at TubeCad are largely conceptual. The schematic at the bottom of page 26 is getting closer to a working circuit, compare with the above.

http://www.tubecad.com/index_files/page0026.htm
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