If you haven't, I'd suggest changing the 6550 if it is that old. If / when it goes it can take out other components in the PS. 3000 hours is the recommended time to replace, I believe,
REF5SE tubes
Time to retube. If tube’s direct from ARC and NOS tubes are not in the picture, what would be next best for tubes? Haven’t purchased anything from Upscale , so that’s out.
Appreciate any and all advice.