274B is very close in all spec details to 5U4G, 5Z3P and even 5AR4/GZ34. The 274B requires a filament current of 2A which is lower than the 5U4G/GB or 5Z4P which would need 3A.
A 5AR4/GZ34 requires 1.9A only. Since that difference is very small most good designed amplifier power supplies should easily accept this. To replace a 5AR4 or GZ34 please refer to your amps manual to make sure this minior increase in current can be tolerated by the amps power supply before you use a 274B instead.
All tubes are selected to the highest grade and re-tested before the shipping.
Suggested burn-in time is 30-40 hours