Help Identifying a Capacitor

[Black Gate]

I recently purchased a Perreaux 6200B power amp from a fellow on eBay. It's a professional amp rated at 270 Watts rms into 8 Ohms. The ad description stated the amp had been serviced every 6 months ... I DON'T THINK SO. Will I ever learn? After receiving it, I popped open the lid and found a layer of dust one inch thick! With my trusty air compressor and cleaning fluid, I removed most of the gunk that accumulated over the years. Not surprisingly, I found some cooked capacitors.

I have attached 3 photos showing the left and right channel PCBs. I have identified the red rectangular caps as 0.1uF WIMA MKS-4 (polyester) and the blue rectangular cap is a .022uF WIMA FKS-3 (polyester).

My question is, what kind of cap is the green rectangular one?

The markings shown on the green cap is .047K 250. Is it a polyester cap, a polypropylene cap, or something else?

For best sound reproduction, should I replace them with exact equivalents or substitute them with polypropylene caps (or better)? Any advice would be appreciated.

The schematic is not enlightening, but for what it's worth, here is the link:

http://i658.photobucket.com/albums/u...x/9b7228cd.jpg

Many thanks in advance for your help.

[peranders]

This green cap is polyester, probably ERO Roederstein, now Vishay. Any polyester cap will do here. 47nF/250V DC, pin spacing 10 mm?

Farnell.com

7.5 mm
Art no
9752412

10 mm
1200737
1614911

[jp-apb]

Those caps are C18 and C19. Part of the output stabilizing section, typically called a Zobel Network.
As noted, any good polyester of the correct value/voltage will work fine.
I don't think a more expensive/esoteric part will make any difference to the sound of the amp.

[Black Gate]

Thanks for your response peranders. Yes pin spacing is 10 mm. Given the board has been subjected to high temperature, I am inclined to change all the polyester caps. Where possible, would it best to use polystyrene, or metalized polypropylene for improved sound quality?

[wintermute]

If you have problems with these caps failing, you might want to consider using some MKT-P (Polyester and paper) caps. My mosfet amp has an RLC network on the output and anything other than MKT-P's apparently fail very quickly, however mine are probably under much greater stress than yours as they go direct from the speaker hot to Ground, the 10 ohm resistors in series on your circuit will probably make it less critical

edit: I did a cap replacement a few years back and where the values were equivalent, I used PPS caps for bypassing (no one else seemed to have used them at the time, but on reading the specs I thought they sounded ideal), certainly didn't seem to have any negative effect on the sound

Tony.