The metal base sounds different than the first bakelite "fat base" or any later Mullard 5AR4/GZ34. I found, in the context of my application (a power supply for an Allnic H3000, where the rectifier is the only tube I roll), that the metal base from Holland (actually, a Philips/Miniwatt) has unbelievably good bass and more "punch" (without being in your face), but in my overall system, it doesn’t have finesse of my preferred tube-- the top octaves are simply not as open or airy.
The Mullards are a standard good old tube, known for good sound, reliable service and long life.
What you’ll usually find in the open market are "pulls"- used tubes that test good. Some of these rectifiers can apparently live almost forever. But finding true never used tubes from WWII and later era is a whole other thing. Andy has been a good source for that.
@immatthewj - did you ever look at that Dubstep Girl’s Massive 5AR shoot-out?
You will not typically find the WE tube at all. The GEC is available usually as a pull, and tres cher. I found a NIB, never used industrial version in Mumbai with one week shipping. I have a brown base too--branded as Brimar, with original box that I put some miles on. Is there a difference, yeah, but the black base I got from India is fine and a "fresher" tube.
The old WWII era double bottom getter RCA is supposed to be the bomb, and not at rarified prices, but it isn’t a straight equivalent to the 5AR4; I have a NIB one, but haven’t tried it.
I rolled, I found a good tube and for my system, I’m sticking with it. But I did go through the process, and have a bunch of back-ups, as well as the benefit of trying different things to optimize. Maybe swapping out rectifiers in some gear makes less of a difference, but for me, the rectifier roll was the most important tube in the Allnic.
The factory tube was tizzy.
