Matched Pairs of tubes are special order directly from Emission Labs. Typical delivery is within 2-4 weeks.
The historical 50 tube, was one of the first higher power triodes for Audio Applications. The curves of this tube are extremely nice, and so distortion will be very low, even at high signal. For that reason, it was originally recommended to use transformer coupling, which method is the safest for high output power circuits. Although the EML50 is much higher quality than the original 50 tubes, and the EML can safely be used capacitor coupled, it is still recommended to use transformer coupling in order to stay closer to the original circuits and design ideas. (Some circuits with the LL1660 will be added to a later version of this data sheet)
Operation and operating points are identical to the historical 50, but it is also possible to use the EML at higher Anode dissipation, up to maximum 28 Watt continuous.
The quality of modern transformer cores is significantly higher than in the first days of tube production, and step-up coupling transformers can be found with perfect full HiFi properties. We officially recommend the Lundahl LL1660 Series here. These have a passive gain of 2.5 and seem the ideal combination with this tube.
Read More Here: http://www.emissionlabs.com/datasheets/EML45-mesh.htm