Stupid electrolytic cap question.......

firenewt · 23rd October 2006, 11:03 PM

I am putting together an SDS Labs power supply capacitor board for my ongoing W-5M rebuild. My question concerns the main caps on the board - 9 47uF 450V electrolytics. The original spec'ed caps are no longer available. Finding the the required value in existing caps is not the problem - the caps are too tall to fit without some modifications to the bottom plate. How much can I increase the uF value before I run into problems? I found the thread concerning blocking so I am aware of that potential problem. So......... how much is too much?

thanks,
Kevin
ps - Feel free to flame if question is too stupid. I am wearing my Russian made two piece asbestos suit with welded fly (with extra pair of pants).

jaymanaa · 24th October 2006, 12:22 AM

I'm not familiar with that amp, what are you using for a rectifier?

paulb · 24th October 2006, 02:19 AM

If you have (or add) a soft-start, there is no upper limit except size and cost.

firenewt · 24th October 2006, 11:45 AM

Sorry, wasn't specific. It's a Heathkit model W-5M. It's tube retified using a 5R4GY tube.

Kevin

soulmerchant · 24th October 2006, 12:26 PM

Download duncan amps PSU designer and modulate your power supply if you want to be fancy. It is free and easy to use.

Don't blow money on excess uF that you don't need...

Go for 105 degree low esr type caps if possible. Don't feel bad about buying cheaper electrolytics though. Some motor run caps work really well in some power supplies i am told.

Be careful if you are new at this... Those caps can hold alot of volts

- please read the safety thread that is at the top of the forum.

I use a big 11 Watt 250 to 400 Ohm resister to ground out every power supply Cap before starting work. Don't use a screwdriver!

Its good practice to leave that resistor B+ (high voltage) to ground during work (some caps build up charge on their own!).

DON'T forget to take it off before you turn thing on again.

23rd October 2006, 11:03 PM	#1
firenewt diyAudio Member Join Date: May 2005 Location: Indiana	Stupid electrolytic cap question....... I am putting together an SDS Labs power supply capacitor board for my ongoing W-5M rebuild. My question concerns the main caps on the board - 9 47uF 450V electrolytics. The original spec'ed caps are no longer available. Finding the the required value in existing caps is not the problem - the caps are too tall to fit without some modifications to the bottom plate. How much can I increase the uF value before I run into problems? I found the thread concerning blocking so I am aware of that potential problem. So......... how much is too much? thanks, Kevin ps - Feel free to flame if question is too stupid. I am wearing my Russian made two piece asbestos suit with welded fly (with extra pair of pants). __________________ It's fun being the only grownup in the house.

24th October 2006, 12:22 AM	#2
jaymanaa diyAudio Member Join Date: Jan 2006 Location: Kansas	I'm not familiar with that amp, what are you using for a rectifier? __________________ "Make everything as simple as possible, but no simpler" Einstein

24th October 2006, 11:45 AM	#4
firenewt diyAudio Member Join Date: May 2005 Location: Indiana	Sorry, wasn't specific. It's a Heathkit model W-5M. It's tube retified using a 5R4GY tube. Kevin __________________ It's fun being the only grownup in the house.

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24th October 2006, 02:19 AM	#3
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	If you have (or add) a soft-start, there is no upper limit except size and cost.

24th October 2006, 12:26 PM	#5
soulmerchant diyAudio Member Join Date: Sep 2006 Location: somewhere near Zurich	Download duncan amps PSU designer and modulate your power supply if you want to be fancy. It is free and easy to use. Don't blow money on excess uF that you don't need... Go for 105 degree low esr type caps if possible. Don't feel bad about buying cheaper electrolytics though. Some motor run caps work really well in some power supplies i am told. Be careful if you are new at this... Those caps can hold alot of volts - please read the safety thread that is at the top of the forum. I use a big 11 Watt 250 to 400 Ohm resister to ground out every power supply Cap before starting work. Don't use a screwdriver! Its good practice to leave that resistor B+ (high voltage) to ground during work (some caps build up charge on their own!). DON'T forget to take it off before you turn thing on again.

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