IMO there are two distinct offerings in 300B's...
Current production 300B's can be either modern, "detail" oriented voicing or traditional "tube" voicing. The European tubes are all in the modern camp. They make no real attempts to sound like WE300B's. The Russian and Chinese 300B's are more traditionally voiced, benchmarking the WE300B sonic signature. (Although, IME, not really all that close to actual WE300B overall presentation)
I agree with PB, the JJ 2A3-40's are modern sounding 300B's with half the filament voltage. I have BH amps with 300B's, 2A3 and 45's. Bear in mind, IMO, the BH amps are, by design, not voiced as traditionally "tubey" amps. I am, for the most part, a tubey sound lover, so I compensate with the voicing of the driver and power tubes. IMO the 45's rule for sheer palpable presence and mid range, (MQ iron with nickel outputs). My Paramount 300B's just do a better job of drive, dynamics and frequency extension than my Paramour 2 45's, (on my speakers). They both do time in the system!!!
Cheers,
Geary