274Bs are a stock item as single tubes and in matched pairs. It is in-stock and will ship quickly. Shipping is free in the US.
274A is a special order from EML and typically arrives in 2-4 weeks.
This Data sheet. is about the 274A and 274B, which only difference is the tube base. These tubes are a full wave rectifiers of a special kind, and electrically equivalent to the original Western Electric historical tubes. Our tubes feature a series connected filament for both diodes together. The series connection makes the middle of the filaments to be virtually grounded, when using a filament supply winding with a center tap. This tube is can supply 140mA with a normal C-L-C filter. The 274A and 274B are designed specially for Audio purposes, and is optimized for use with a small size first capacitor. With this tube, you will have only normal rectification current flowing in the rectifier circuit, and no heavy current spikes. This will result in less hum radiation into of the preamplifier, an improved sound compared to low impedance rectifier tubes for industry applications, or solid state rectifiers. Also the 274 is specially suited for applications with relatively high DC voltage. The new ceramic sockets we use, are a good help for this, since these give no leakage, and do not age under high voltage.
For ultra low ripple, it is recommended to use the Lundahl LL1673 dual coil choke in low CMR configuration. In this configuration, there is virtually no field radiation from the choke. (See link to circuit diagram, at the bottom of this page).
Read More Here: