What's your best 5U4GB rectifier tube and why?

I recently acquired a 9 watt Class A design 300B tube integrated that came with a 40's NOS Japan 5u4gb rectifier that I wanted to compare to some of the best that's available. I'm new to tubes so I'm asking for your expertise.

It would be helpful to know why you're high on your particular tube recommendations and what differences one could anticipate with those you're suggesting to sample. Acquisition cost for same would be very helpful as well.

My amp is currently running with a pair of Shuguang Black Treasure 300B's and a pair of Black Treasures 6CA7's, in conjunction with a pair of Psvane 12AX7's all combined with the 'rec mentioned above.

Thanks in advance to all for the assist!

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The sound of a tube is heavily dependent upon the design of the circuit it is used in. What sounds best in one design may not be the best choice in another application.
I know very little about tubes but Peter Q of Audio Note UK told me to buy the coke bottle shaped 5U4GB tubes for best sound in my Meishu 300B amp.

Obviously there is much more to it but I am guessing on some level he is right...

As Onhwy61 said, it depends on your circuit. If your amp will run OK with a 5U4G that opens the door to some nice black plate RCA's or perhaps some Mullard GZ32's which can be very nice. The Mullard GZ37 High Wycomb are wonderful in some applications. If you're stuck with 5U4GB, I think the Tung-Sols are about the best sounding in the various amps where I've used them. Currently, I'm using some Sylvania 5931's in my Pilot SA-360 amp and a Mullard GZ32 in my Modwright Transporter. But I didn't like either of them the other way around, that is, with the Sylvania's in the Transporter or the Mullards in the Pilot (altho they *were* pretty nice there).

In other words, try some varieties assuming they will meet the electrical requirements of your amp. Check with the maker, or check specs on Duncan Amps site.

Hope this helps!
I'm surprised no one has mentioned the EML (Emission Labs) 5U4g mesh. In my Modwright Transporter, and in my Woo headphone amp that rectifier was wonderful, and topped my list when rolling in both applications. YMMV according to the application/circuit that you are using it in though, but the EML is most definitely a contender for top billing.
I acquired a pair of NOS Tung-Sols to sample first. Frankly I'd be surprised to hear if swapping rectifier tubes will make a noticeable difference but I'm open minded.

Thanks to all who chimed in w/ suggestions!
they made a huge difference in my 300B SET

good luck
is you amp by chance grant fidelity?
I agree with the NOS recommendations above. It's worth trying a few. The coke bottle RCA black plate and GE 5-rib skinny 5u4g have been exceptional in my Melody Pure Black 101 pre, in Quad amps and in my guitar amps where appropriate.

But I wanted to mention one current production inexpensive tube. Tubestore.com has a private-labeled and highly-tested version of the Shuguang 274B. It is available as a Shuguang tube, too, I think, but with Tubestore you can be sure. It is a heavy glass, large plate 274B with a lighter 5ar4-like filament current draw, and has much harder vacuum than the basic Shuguang tube. These are under $30 each, and have sounded very fine in anything I've tried them in. They feel robust, haven't flashbulbed like so many other current production cheap rectifiers. Absolute longevity is TBD. It's borderline for some amps, like a Mesa Mark V, that are aggressive with voltage, but it seems copasetic with most hifi amps stocked with 5u4 rectifiers.