Your best bet is to get a pair of 596 tubes but these are starting to get hard to find.
Next best thing would to get a pair or 5U4GB these are stronger then a 5u4G
I know nobody likes the 5U4GB it is not as pretty but a much better tube the 596 and 5U4GB
are electrically close. If anybody says the 5U4GB don't sound good I say BS.
One thing when you buy new rectifiers they have to be the same brand and vintage
or the filaments won't worm up evenly and one tube will blow up
Amen to the 5U4GB. I've tried the Tung Sol and RCA variants, and while they may not be on the same level as the better rectifiers, they still perform well and are very cheap. I prefer the RCAs by a hair, but the Tung Sols are not shabby at all. For $30 for a pair of NOS US-branded 5U4GBs, don't bother with cheap 5AR4s.
I remember the hoo-haa about the EML 5U4G in the WA-5, but did anyone face any problems with it in the WA22? So far mine has hit about 1000 hours, and the only time it misbehaved was when it sparked once 5 minutes into warm-up. That was a few months back and it's still going strong.