Philips Holland Factories
Pope, Valvo, Adzam, Amperex, Mullard, Miniwatt Dario, and Radiotechnique were all names owned by Philips Holland.
The respective names typically referred to factories. For instance, Mullard operated in England, Valvo in Germany, Amperex in the U.S.A., and Radiotechnique in France. In the case of Adzam and Pope, these were names to export Philips products into other markets such as Latin America and Africa.
All of these factories may at one time or another produced tubes with various other names attached, which is why we see Amperex and Mullard tubes made in Holland, or Philips branded tubes made in England. Factory codes etched on the tube help us to figure this one out: For instance tubes with a "delta" symbol refers to the Philips factory in Holland.
The type of tube can also be helpful in figuring out what factory made the tube. For instance, it's common to see 6922 (E88CC) and 7308 tubes made in either the U.S.A., France, or Germany. On the other hand, Philips only ever produced 6DJ8 (ECC88) tubes in Holland. It goes on and on.
On thing is for sure...regardless of the name...pretty cool stuff.