Not just an replacement, but an improvement!

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 plate 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.

Features 

• Gold plated Grid
• Center tapped filament
• Hard metal Construction (Note1)
• Two extra large getters
• Hand blown Glass bulb
• Anti-microphonic plate- and grid  suspension
• These tubes are shipped in a high quality dual box
• Tube printing with real gold (metal),  red color is glass burned into the glass 
• Machined, solid tube base pins for highest contact precision. YAMAMOTO tube sockets highly recommended. 
• Gold plated pins,  black ceramic socket.  (White bottom.)

• Note 1)  Hard-metal filaments prevent filament breakage with DHT Tubes.  This material has a higher melting point than the classical nickel wires. Wolfram grids  allow the most precise grid wire distance, because wolfram is an extreme hard metal.   This ensures better grid  precision, which gives uniformity and better linearity at the low end of the tube curves
• Note 2)  Individual Test data:  Grid voltage, Plate current, Transconductance and Filament Current is the test certificate that is on the outside of the box. Each tube is numbered, inside the bulb  with a metal Tag
• Note 3)  Tube Curves:  Made on the The Sofia Curve tracer.
• Note 4) The historical 50 tube was specified with max 10k grid resistor. This is a very low, inconvenient value. The high grid quality of the EML tubes, allows for the much higher values, which you find under "maximum specifications". For downward compatibility, meaning the option to use historical 50 as well, you are advised to use a maximum 10k resistor. Alternatively the Lundahl LL1670 grid choke can be used, instead of a grid resistor. This ensures downward compatibility as well, and with a grid choke, you don't need a grid resistor.
• Note 5) Here is a link to the historical datasheet, from the RCA tube manual