Rectifier tubes?

I cannot speak from experience with this exact product but in general, NOS tubes are far superior to new stocks.

My luck with NOS 5U4GB has obviously been better than yours. My first choice would be Sylvania Gold Brand with old Tung Sol running a close second. My tests and reliability results were (as I remember) with Tube Research GT 400 and Mike Elliott's EASE Magnum.

Here is a link to BWS tube who has them in stock.

http://www.bws-tube.com/htm/tubes.html

NOS 5U4GBs are dirt cheap. $5-$10 each. Cheaper than the new ones. Shop around on ebay and try several different flavors for little investment. RCA, Sylvania, Tung Sol etc. Just look at the ones offered for carefully. Do they appear to be NOS. Original boxes; JAN military boxes; etc. Don't mess with the used crap at these prices. Have fun. If your amp can use 5U4Gs (225ma vs. 275ma) you might want to look into these. More expensive, but in my Cary SLI-80 much better sonically. Also, if your amp can use the 5U4Gs, look into some NOS 5AS4s. A pair of Mullard 5AS4s worked magic in my amp. Good luck!

You shoulc contact Sophia Electric. They make a 274B solid plate or mesh plate that could be magic in that amp.
www.sophiaelectric.com

They are very nice folks too!

You can look at many options like the GZ37 or 5R4GYB. GZ34 might work in some applications too