A while back one of the 6550s in my Traynor YBA200 went out with a spectacular flash and I ran it with two tubes pulled with a 4-ohm speaker on the 8-ohm setting for a while. I just retubed it with JJ KT88s a week ago and although I like the way it sounds, after 5 on the gain and 5 on the master, it just loses it; nasty, hairy distortion cuts in and out intermittently, but always cuts in on the attack of the note. There's a 5751 in the preamp, so it's not the usual problematic YBA200 distortion; it's definitely related to the power section. I've heard that the cathode bias on the YBA200 tends to not quite match up too well with some KT88s, so maybe this is crossover distortion, but I opened up the chassis to look around and pin 8 of the socket for V6 is scorched, as well as the both ends of resistor 64 (R64). The traces in that area are fine, and once I can get a multimeter I'll test R64 to make sure its value is still correct, but in the meantime, could anybody check out the schematic and offer any advice as to what could be causing this, if I may have a bad screen resistor? Any help would be appreciated. Here is the service manual: http://www.traynoramps.com/downloads/servman/smyba200.pdf R64 is at intersection L9 on page 1 of 2 of the schematic (1W, 10 ohms) And here's an example of what it sounds like: http://www.mediafire.com/?9ld3b15zjbb It's really too bad, because I was getting some great headroom out of this and I may need some real volume out of this amp pretty soon. Also, I am very aware of the dangers of opening up a tube amp, and am being duly cautious.