Not just an replacement, but an improvement!

EML 50

Uploaded: 23-Nov-2014


Description 

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.)

EML 50

Side - Front - Bottom
Night view

 

EML 50  Filament Ratings 
Filament Voltage 

= 7.5Volt (AC or DC)

Tolerance on filament voltage
5%
Filament Current 
~ 1.25Ampere 
EML 50 Maximum Conditions
not possible simultaneously 
Plate Voltage 
500Volt 
Continuous Plate Dissipation
28Watt 
Peak Plate Dissipation
(Not continuous)
35Watt 
Plate Current 
120mA 
Grid resistor with Auto Bias
250k Ohm (note4)
Grid resistor with Fixed Bias
50k Ohm (note4)
EML 50 Factory Test conditions 
Plate Voltage 
400V 
Plate Current
55mA 
.
EML 50 Typical Data 
Plate Voltage 
350V
400V
450V
450V*
Plate Current 
45mA
55mA
55mA
62mA
Plate Dissipation 
15.8Watt
22Watt
24.8 Watt
28 Watt
Grid Voltage 
63Volt
70Volt
84Volt
81Volt
Plate Impedance (Rp)
1900 Ohm
1800 Ohm
1800 Ohm
1800 Ohm
Amplification Factor 
3.8
3.8
3.5
3.5
Transconductance (Gm)
2mA/V
2.1mA/V
2.1mA/V
2.1mA/V
Power Output in Class A 
2.4 Watt 
3.4 Watt
4.6 Watt
6 Watt
Load Impedance (Ra)
4100 Ohm
3670 Ohm
4350 Ohm
4100 Ohm
Recommended Lundahl SE output transformer
LL1679-70mA
LL1620-60mA
LL1679-70mA
LL1679-70mA
Recommended Drive transformer **
LL1660
LL1660
LL1660
LL1660

* Fourth table (450V/62mA) not allowed with historical tubes
** Choose driver tube DC current before ordering the Lundhal LL1660 drive transformer. Available is 10, 14, 18, 25mA. Wire for " ALT S" to get a 1:1 interstage. Alternative wiring can be chosen to get a 1:2 step up.


alternate textPrint Version

Download these curves as PTE file - What is that?

EML 50 Mechanical Data 
 Size including Socket
(but excluding pins)

145 x 58 mm 
5.5 x 2.3 Inch 

Single Tube weight 
145 Gram 
Shipment weight for 
pair in gift box 
700 Gram
  • 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 data sheet, from the RCA tube manual

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