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Class A power Supply
Class A power Supply
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Old 16th February 2012, 06:30 PM   #1
alibear is offline alibear  United Kingdom
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Default Class A power Supply

Hi all,i am building a C-L-C power supplyfor a classA amplifier.The filter capacitors i have are new Epcos 47,000 at 40V and the transformer has secondaries of 25-0-25. After full wave rectifacation I am getting almost 37 volts when drawing a bias of 2 amps. My question is: is this too near the operating voltage of the capacitors for safety and long life and if so could I place a 1ohm resistor between the bridge and the first filter cap ( in both the positive and negative rail ) to reduce the voltage by a couple of volts or will this cause any problems.
Thanks for your help
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Old 16th February 2012, 06:38 PM   #2
GloBug is offline GloBug  Canada
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IMO which is almost worthless, you need a little more room for variations in power line voltages and potential surges.

50V or 63V caps would be ideal for a 25v transformer.

That being said, I had a Bryston here that had 49V rectified rails with 50V caps that ran daily for almost 30 years.

I guess it depends if the caps are conservative in their ratings.

Different caps would be my first choice, unless you find smoothing advantages in using the resistor. How many volts can you drop? You may find it impractical to get the voltages to the proper safety level without hindering performance.
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Old 16th February 2012, 06:41 PM   #3
bobodioulasso is offline bobodioulasso  Europe
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I wouldn'nt worry about 37v rails and 40v caps.
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Old 16th February 2012, 06:41 PM   #4
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
This resistors will degrade the supply regulation, and the capacitor working voltage is wright. Normally, the vent voltage is as 50% up the normal WV. Donīt care, and keep out these resistors.
Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.
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