I ended up using a 5U4G. Not knowing anything about circuits, I just thought I'd give it a shot and it worked. I just assummed it was being used as a rectifier. I was too impatient to swap tubes in one at a time, so I also put in some Sovtek 2A3s and it made a big improvement in sound.
5Z3PAT equivalent
I just purchased a Bez 2A3 amp from China. Does anyone know if the 5Z3PAT rectifier can be replaced with a 5Z3? If so, any recommendations? There is no manual and I have not heard back from the seller. So far, the sound is quite thin out of the box, but I'd like to try some NOS tubes in it and let it break in before I form any final judgements. It DOES have a very transparent treatment of the vocals that I like, so may be worth tweaking.