Some info about the original question. I think the 5AR4s were made in England in the Blackburn Mullard factory but were sometimes labelled Amperex. Phillips was a Dutch conglomerate that owned many tube brands, Mullard, Amperex, Siemens, Valvo, and on and on. Tubes made in one factory could be labelled with the brand of a different factory. The way to tell where and when a tube was made is to check the codes etched into the glass of the tube. here is a list of the codes and how to interpret them:
Any tubes you come across today will be "New Code’ so just ignore the ’Old Code’ stuff. Also etched tube codes can be hard or impossible to read, but that doesn’t necessarily mean the tube is a fake.
For example look on page 11 of the linked document for a lower case f and 3, f3 and you’ll see that’s the code for a GZ34 (AKA 5AR4)
There were also many other tube makers who had their own way of identifying tubes, for example, Telefunken, RCA, GE, etc.