@wrm57- not a problem. I mistyped your screen name earlier. I did find another cup base GEC U-52, this time a black base, not a brown base. I think it is an earlier production, although someone else who had a lot of these said that the brown base was preferred (my brown base tube still has some life but had some time on it), and the fresh black base sounds fine. Doesn’t surprise me that Kron is not readily available. Are they still in business?
When I retubed everything (all components, not just the Allnic), I did get old stock Holland E810Fs. I had bought some a few years before, never used them, but they were printed on the glass as made in Great Britain. I later learned they were made by Amperex in the States. Apparently, during the golden age of tubes, affiliates took overflow and since both were owned by Philips, no problem. My seller was surprised to learn that- I didn’t return them, they are in one of those boxes of "fresh" old tubes stashed away here.
Even having been in this market for decades as a consumer, there is a lot to learn and nuances that aren’t obvious to the uninitiated- all the more reason to source tubes from a trusted seller. Andy is one of the best I’ve encountered in the States since the Great Disappearance™ of Elusive High End Tubes, but you have to be patient. He can’t always scratch the itch when you need a tube, pronto.