Note, Emission Labs was the first to re-introduce the 274A again, in the year 2001.

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 virtially no field radiation from the choke. (See  link to circuit diagram, at the bottom of this page). 

• Slow Start ( 2...7 seconds)
• Filaments are series connected, for best symmetry of the two diodes inside.
• Two extra large getters
• Each tube is numbered, inside the bulb with a metal Tag
• Two extra large getters, flashing the complete tube bottom
• These tubes are shipped in a high quality box
• Tube printing with real gold (metal), red color is burned into the glass
• 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. From Yamamoto, the Octal 8/5p Teflon socket is recommended. 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. Like this you can never put in a non-rectifier tube by mistake. You can also use normal octal sockets of course.

• See: CIRCUIT DIAGRAM 
• See: Note 2

274A Mechanical Data
	Tube Size including Socket:  140 x 58 mm  5.5 x 2.3 Inch
Tube weight	130 Grams
Shipped weight for  double box with one pair	730 Grams

274B Mechanical Data
	Tube Size including Socket:  147 x 55 mm  5.8 x 2.7 Inch  Connections: Filaments: 8 + 2 Plates: 4 + 6
Single Tube weight	125 Grams
Shipment weight	400 Grams

Note 1) Hard-metal filaments prevent filament breakage with DHT Tubes. This material has a higher melting point than the classical nickel wires. 

Note 2) To prevent large charge current peaks, the first capacitor (C1) should NOT be larger than 4uF. 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.  For ultimate filtering,  with oversized components, you  will have best  results by increasing the choke.  Do not oversize capacitor C1, this  will not give better  results.