I appreciate the advice about getting a vintage 5Y3, and probably will eventually, but just to satisfy my own curiosity I picked up a modern JJ 5Y3S.
I also pulled the vintage GE 5V4 out of my '63 AC30, the Chinese 5AR4 I started with, and the Sylvania 5U4 that came in what started life as a '74 Fender Pro Reverb.
I set up a test to see just how different they are. I used my Gibson GA-10 (now 5E3) as the test bed. Loaded with JJ 6V6GTs and modern JJ 12AX7s (for now). With a Variac set at 120vac, here's what they produced:
The PT secondary AC output with no rectifier tube installed:
730vac
5AR4:
Loaded PT secondary - 683vac
Loaded B+ - 389vdc
5V4:
Loaded PT secondary - 685vac
Loaded B+ - 382vdc
5U4:
Loaded PT secondary - 685vac
Loaded B+ - 373vdc
5Y3S:
Loaded PT secondary - 685vac
Loaded B+ - 352vdc
I didn't measure the current capability for this test, as I don't have the equipment to do so, and that wasn't the point of this exercise.
The 5Y3 definitely dropped the B+ down into the range for what I wanted for this project, so thanks to everyone who chimed in on my other thread. I may end up buying a vintage 5Y3 later, but for now, this makes me more comfortable to continue with this project.
Thanks again - this place rocks.
