How does it affect power supply operation if filter caps are doubled in size?

With the supply that you describe the result will most likely be a little better filtering. This may raise the average output under load but you mention no regulation anyway. Are you sure the caps are in series? Series filter caps are not the norm. Regards, Tom

I've got a power supply that has 2 470uF 400V filter caps in series. The power supply puts out 400VDC.

Now if I change the caps to 1000uF 400V, what will happen? Will the output voltage of the supply change?

(this is just a basic supply that fullwave rectifies AC with diodes, then comes the filter stage between the supply voltage and ground)

-at

Good morning. You didn't say if you've got 120VAC or 240 VAC input. Here's one way you can get "400VDC" from 120VAC using two caps in series (view in fixed font or M$ Notepad):

1N4006 o-----o--->|----o-----o+ | +| 120VAC | --- | C --- | | o-----|---------o "400VDC" | +| | --- | C --- | | '---|

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Hi at, It would help if you told more about your application for this supply. You sound as though you have little experience with high voltage supplies, be careful. You are describing very old design charistics. If you are working on and old radio or other old device tell us what it is. Regards, Tom

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Thanks. There are 2 caps in series, I guess it's to give better voltage handling capacity.

I've got one other question.

Now if I change the diodes into a rectifier tube, that has a max capacitance in the first filter as 60uF, and after that I place a resistor or a choke, what is the max capacitance the second filter stage can have (it's after the resistor/choke)? I've heard people tell me it can be bigger than the first stage, and I've heard it cannot. So I'm somewhat confused what's the truth. If I use a resistor, does it isolate the second filter stage from the first? If I use a choke, does it do the trick?

If you've got a regulated power supply, does that make things different?

-at

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Thank you for your reply.

It's good to know how it works. If there's a problem with the higher DC voltage, I'll increase the resistor size in the power supply. That will drop the voltage some. Or is there a better way?

Don't the filter stages also drop voltage? Or do they increase it? Is it the resistors between the filter stages that make the voltage drop, and not the caps? If I put resistors parallel with the caps (as is sometimes used), the resistors will also drop some voltage, is this correct?

-at

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This is just an example supply that's like many used in old tube-based audio equipments. I know the dangers with high voltages, I'm not going to get hurt. It's true I don't know much about the theory details, that's why I'm writing to this basics newsgroup. I would like to know how the capacitors work so I could see if I could benefit from better filtering. Big cans are expensive so it's better to ask questions before deciding. I just would like to know how big capacitors you can put into an tube amp with a tube rectifier. I would want to get good filtering, so I'm interested to know if I could put bigger caps in the other filtering positions, than what the tube rectifier allows for in the first filter position.

-at

I believe in your response to another answer you mentioned you've got one of those "old tyme tube-type" setups. In days of yore, back when "men were men and women were glad of it" (Three Stooges), they did something like this (view in fixed font or M$ Notepad):

1N4006 ___ o-----o--->|----o--|___|-o----------o | +| R | 120VAC | --- --- | C --- C --- | | | "400VDC" o-----|---------o--------o | +| | | --- --- | C --- C --- | | ___ | '---|

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Back in the day, we liked the time constant discharging the caps to be at least three times that of the charging time constant. What do those terms mean? You should be able to find something and bring your questions back. Good Luck, Tom