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.
Phil
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.
Phil