After a few minutes of operation the Sunfire MKII starts humming. I think it is the caps at the power supply. Does anyone have a better idea and where can one purchase parts for Sunfire?
Capacitors are a GENERIC part. You do NOT need the sunfire part # or to source parts thru them. The probably (99% chance) won't sell to YOU, anyway. Polar should be replaced WITH polar, while bipolar caps are OK where they are a direct replacement. Other materials have been used over the years for mainly small value caps in radios and other RF applications.
Sources would include everything from RadioShack or Frye's all the way to Digikey, Parts Express and even perhaps Madisound. Bunches of high-end parts retailers exist online who would be MORE than happy to sell you some goodies.
Look on the suspect caps. You will see the 'value' in Microfarads. A Voltage which is the MINIMUM to accept in the new part and sometimes a Temperture rating. Higher is better. About the highest temp rating would be 105c. Others will be 85c. Depends on how HOT the manufacturers testing indicates the product gets and if the extra 'insurance' value is important to them.
The MAIN problem is WHERE on the board the part goes and IF the new one fits. Some speaker caps, for example, can be somewhere between really Large and Absolutely Gigantic.
Have a good soldering station at the ready, a solder sucker and solder wick. You'll also need a selection of HAND TOOLS like needle nose pliers and some flush-cuts. A wire stripper MAY be required, too. Don't forget some High Quality solder. Kester 44 RosenCore is a 'standard', though OTHERS swear by 'special' stuff, mostly including a small amount of Silver.
If you've never worked on this kind of thing before, you SHOULD DEFER your experiments till later and if you want a working sub, get a real tech to have a go at replacing parts for you.