arp pro/dgx power supply cap replacement

[us3rx]

Hello
I'm in the process of teaching myself and my daughters about electronics and music synthesis. Our fist project is a bipolar power supply (+-10 - +-15). I have a Arp pro/dgx that we are wanting to use for a chassis,keyboard,etc.. When I powered it up I got sound (a very loud hum that can be modifieid through some of the filter controls) and lights. I couldn't discern any pitch changes when hitting the keyboard.
At this point I thought we had are power supply ready made. Referencing the schematic I tested the output and found I was only getting +6.25-+6.4v d.c.on the +15v output. When I switch the meter to autorange AC/DC it will flash between +6.4v dc then to ~7.5ish ac. I'm going to replace the big caps first. I would like to use something off the shelf to replace just to test the circuit further. Can I use a Nichicon 330 my local Radio Shack in place of the 250? I've taken other measurements from the circuit both AC and DC which I can post if it would help.

[Nigel Goodwin]

Assuming they are actually 250uF, then 330uF would be fine - but 250uF is a very low value, so presumably it's only a low current supply? (notice the 3300uF on the other supply).

[us3rx]

thanks for the reply Nigel.
I checked the writing on the caps "250MF 50V" the part number is "TT50X250A". it measures roughly 1cm dia. x ~3.5cm length.

[indianajo]

Power supply caps can be up to 40% higher in value (before the turn on surge burns up something) or 50% higher in voltage rating (less the chemical effects cause something non-linear). Tuning circuit caps, usually rated +-10%, have to be matched by tight tolerance caps.
Nichicon makes 1000 hour caps and 8000 hour caps. I prefer the latter when working on something I might keep. I don't buy surplus electrolytic caps, they might be old, and the seal deteriorates on the shelf unused. Newark.com has the hours life in the selector tables to allow you to select the quality line. Other vendors you have to click on the link to the datasheet and read it. Panasonic, for example sells some caps with the same prefix, some of which are 1000 hours, some of which are 3000 hours. The more hours, the better the seal at the seams of the aluminum can. To keep my shipping costs down, on devices over 20 years since re-cap, I order them all on one order. I'm getting $6.70 UPS NC to IN. Mouser.com TX to IN is $9 minimum. From california I ask for USPS priority ship, it saves over the long distance.
You must live on the coast, because my local Radio Shack has telephones, toys, and batteries. No components.