Hi soundtec - I think you forgot to post the comparison you mentioned.
By coincidence, I've just received a 6800 which I ordered a week ago, just before C82 blew on the 6600. It's got a KKMoon logo on the front instead of FE, but it's still a Feeltech instrument - just 20% cheaper! I was just about to use the £20 saving to buy a D75J oscillator for it, and replace the THS3002 with 3095s as in the FY6600, but then I thought I may as well try the 3491s instead to see what happens. They'll be a big improvement over the 3002, I know, but now I'll be able to do a comparison against the 3095s as well, where the difference might not be so visible.
The under-load voltages from the SMPS are 4.958, +11.792 and -11.953, so pretty good except for the +ve rail being a bit low. I'll see how it gets on before I consider any mods to the PS this time.
The D75J is an essential though - I did a frequency stabilty test starting them both from cold, and the FY6800 took over 50 minutes to settle down, compared with just 10 minutes (probably less) for the FY6600. The total deviation was 41ppm for the FY6800 and just 1.5ppm for the FY6600, so it was a no-contest.
Amusingly, the FY6800 came with a non-UK mains lead and an adapter plug - which has a plastic earth pin!! I suppose the seller would claim he just sells them, and doesn't have to know anything about them?!
Dave