by EdStiles » Fri Feb 22, 2008 9:30 pm
The 50/50 mfd @ 560 vdc are JJs, they were purchased while back from Eurotubes.com. I just went to their site and don't see these anymore, I do see a 32/32 @ 560 vdc, which would still be a reasonable solution for the last 2 sections as the Dynaco originals were 20/20. The JJs are rated at 560vdc, but that is an absolute rating; the surge and operating are the same as I understand it (which is why I use them in the last sections, startup with the 5AR4 may exceed 560 vdc). I installed them under the chassis to shield them from the heat of the 6550s and 5AR4.
The site listed above for FT caps has a 20/20/40/40 at 550 wkg / 600 surge vdc, that might be an option, especially as it is a twist lock (if used with an under-chassis board like the SDS.
One other option that I am considering for my amp is to use only 3 sections of the SDS board to make a 100 mfd B+ section, then adding a second small (20 ma, 10 Hy) choke and isolating the driver board from the B+ tap: the configuration would be 50 mfd -> C354 _> 100mfd for the B+, the first 50 mfd section would be shared so the driver supply would be 50 mfd -> small choke -> 50 mfd (4th section of SDS) -> 6.8K -> 50 mfd (JJ)-> 2nd resistor -> 50 mfd (JJ)
You might want to call Eurotubes and see if they can special order the 560V cap.
Ed