This tube is a full wave rectifier, electrically equivalent to the original Western Electric historical tube.
274A is electrically equivalent to 274B, but we stopped making 274A. The difference is only the socket. 274A has a UX4 socket,274B has an Octal socket.
In case you need really 274A, we recommend the EML 80-R tube. This tube, can directly replace 274A.
The EML tubes feature a series connected filament for both diodes together, which has certain advantages.
This tube can supply 140mA with a normal C-L-C filter. AT these conditions, the 274B is designed to be used with a small size first capacitor of 4uF only.
At lower voltage, lower current, it is possible to use a first capacitor of 20uF.