Now that I have your attention, here is something that seems to be a problem with the New Sensor Corporation's KT66 Gold Lion reproduction tubes. Purely COSMETIC issues, but it is still an issue for me at least:
I have about 400 or 500 hours of usage on my set of KT66 tubes in my ST-70. The glass surfaces of tubes tend to become dull after extended usage (deposits / dust or whatever), and in the past I have always cleaned it by washing it with a mild soapy solution (non-ammoniac!) and leaving it for at least 2 hours to dry. I know for a fact that the gold insignia and lettering has never had a problembefore, but yesterday I did the same thing and all of a sudden, the gold lettering and lion insignia literrally came off like decals on an old cheap plastic model plane.
So... I checked the next tube and seems I can easily scratch off the lettering with my thumbnail - something I know I could not do a year ago at all (I know, I tried to get rid of the prominent "Made in Russia" lettering when the tubes were new, and could not budge it at all)
So... seems extended exposure to heat destroys the gold lettering on these tubes. Sonically these tubes still sound as good as new (actually better) but if cosmetics are important to you, be forewarned!
Best Regards to all