Check tube bias after any rectifier swap.
A different rectifier can be higher or lower voltage, and affect bias.
John C.
Great post! That's why each rectifier seems to have each own signature on the overall sound. It is not because it is NOS/Blackplates/GT/ST/etc. but because it changes the B+ and shifts the OP of the input/output tubes. For example, the 5V4 have a voltage drop of 25 V, 5Z4 at 20V, and the 5AR4 at 17V.
For the 5V4, I would suggest to check out the RCA ST type http://img518.imageshack.us/img518/4678/img4488td5.jpg
regards,