Not just an replacement, but an improvement! Emission Labs was the first company to re-introduce the 274 tube again, in the year 2001. The first owner can register the tube at the Emission Labs website, ripple factor of full wave rectifier participate in the 5 years guarantee program. 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. 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.
Filaments are series connected, for best symmetry of the two diodes inside. 274A has machined, solid tube base pins for highest contact precision. Ideal for the YAMAMOTO tube sockets. Starting May 2011, we have started to ship the 274B-mesh with the new ceramic socket, with five pins. This is an octal socket, but has five pin holes only.
It is specially used for this rectifier. When working with Octal sockets, you will find the Yamamoto an amazing top class product. For this rectifier you can take the special octal version with five holes only. READ all notes at the bottom of this Data sheet. 24uF, a limiting series resistor must be used, so the peak in-rush current through the choke is limited to the saturation current of the choke, or max 600mA, whatever comes first.
Can not be calculated in a reliable way. For lowest hum, this resistor is in series with the choke. So you get a C-LR-C filter. In this way 200uF is possible. Hard-metal filaments prevent filament breakage with DHT Tubes.
This material has a higher melting point than the classical nickel wires. If the input capacitor is too large, this will result in heavy AC charge current through this capacitor. This is not good for the rectifier tube, and also the AC capacitor current peaks may cause hum radiation into the preamplifier. With the given C-L-C values in table, the rectifier circuit will work without any trace of hum.
SOME DESIGN NOTES FOR POWER SUPPLIES. This is probably the most misunderstood part of a tube amplifier. It can be a mistake to simply copy something, just because it was presented as “very good”. Cases where good design rules were not respected we find as well with companies of high reputation, as with any other company. Do not treat tube diodes like solid state diodes.