Not just an replacement, but an improvement!

EML520B-V2
EML520B-V3
EML520B-V4
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Description

The 520B is a long plate Version of the older 52B, with many technical improvements added. The EML520B is a state of the art product, in the family of the 300B tubes. This powerful tube is recommended for new  designs. The 520B has the  same outside dimensions as the "845" tube, but longer plates. All critical parts, like filaments, grids and plates are constructed of hard metal for higher reliability and reproducible quality.  Note the relation between the tube base, and and the glass bulb. Then compare this with our 300B.   This gives you some idea of this tube's size.

Versions:

520B-V2 6.5V Filament Originally made for some amplifier manufacturers. Available as spare part.
520B-V3 5V Filament Standard tube since many years.
520B-V4 5V Filament with Balanced Heater Special version for "no Resistor" bias scheme. Later, an application note will be issued. At the moment, this information is here.

Applications:

1) Use as large 300B tube.

Though this is no drop-in replacement for 300B, you will often be able to replace a 300B. Care needs to be taken to have the right bias, and also you need to make sure the filament voltage is 5 Volt. With some knowledge of electronics, you will find this tube a superb replacement for 300B tubes. One of the best things you get with the 520B is the lower plate resistance (480 Ohms of 520B vs 700 Ohms of the 300B). This will lead to higher efficiency, and a gain of output signal, even at the SAME bias settings. The lower plate impedance will give better control of the BASS speaker chassis, since the damping factor increases with 25% compared to standard 300B.

2) Use as large SE 300B alike tube.

The higher bias which is possible with this tube, will allow you to build 18....20Watt SE amplifiers.

3) Use as Push Pull tube.

The 520B-V3 is ideal for Push Pull applications, since the higher peak emission (vs 300B) will ensure much longer lifetime for the 520B, vs 300B. Occasional overload of a push pull stage is hard to prevent, of the user overdrives the amplifier. Other than a SE stage, the power dissipation of a Push Pull stage is quite dependant of the maximum output signal, and rises even sharply if you drive a PP stage into distortion. Unlike the previous models (called 52B), the 520B is not immediately taking damage if the tubes are used above maximum dissipation. Of course we can not specify how far you can exceed the maximum, but the thermal capacitance of the anode is very large, and this is the best protection against accidental (short time) overload. Another protection is the special grid, which will not develop grid current after occasional overload of the Push Pull stage. Last but not least we use a special anode composite, which allows very high dissipation.

Features

  • Double Mica tube top (Note6)
  • Gold plated, Wolfram Grid
  • Soft rubber suspended tube base
  • Center tapped filament
  • Slow Start filaments, for best lifetime
  • 0.5 mm thick plates
  • 10 circular coolers (4 single + 6 double plates)
  • 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.)
We have two versions for the heater: Normal heater, or Balanced Heater.
 

With the Balanced Heater, we enter an entirely new field of applications. This has not been done before with Audio tubes. When biasing a DHT tube there is no cathode to connect something to. The cathode must be artificially constructed, by a resistor network. Since many years, all EML tubes already feature a center tapped heater, which is a way to enforce better electrical field geometry. Only, this center tap has no electrical connection to the outside world. To the tube itself we had to make no changes, it is just we connect center tap to the socket, which becomes the third connection of the heater. Now the tube has five wire connections, and for this reason we can not use the 4 Pin UX4 base any more. We have chosen for the Octal base. It must be said, the V4 is a very special tube, which fulfills the needs of Circuit Design purists the best possible way. Depending on how you do it, you can enter new design fields, or you may choose to connect the center tapped tubes just the classical way. Even so, for tube testing you can ignore the center tap, and just connect the tube the regular (four pole) way. In that case, the EML1605-V4 will behave like a standard four pole tube. In the case you own center tapped tubes, but you whish to connect them like a non-center tapped tube, this is possible too. In that case just do not connect the center tap.

Link to Application Note AN-6 about balanced (center tapped) heater tubes is here


520B
Detailed image


520B
UX4 Base


UX4 Socket


520B-V4
Octal Base


Octal Socket

 
 
Important
Read all notes at the bottom of this data sheet before installing this tube.
.
Filament Ratings (See note4 and 5) 
 
520B-V2
520B-V3
520B-V4
Filament Voltage (AC or DC)
= 6.5 Volt
= 5.0 Volt
= 5.0V with Balanced Heater.
( 2x 2.5V )
Tolerance on filament voltage
5%
5%
5%
Filament Current
~ 1.5 Amp.
~ 2.0 Amp.
~2.0 Amp.
.  
Maximum Conditions
(Not possible simultaneously) 
See also Note4.
Plate Voltage 
550Volt 
Plate Current 
200mA 
Tube Output Power
24 Watt

Highest possible Grid to ground resistor, Single Ended.

150kOhm 

Highest possible Grid to ground resistor, Push-Pull.

50kOhm 

Typical application
Recommended operating point
See also Note3.  

All bias methods are possible

Plate Voltage 
458V 
Plate Dissipation 
55Watt 
Plate Current 
120mA 
Grid DC Voltage 
-91Volt 
Plate Impedance (Rp)
 520Ohms 
Unloaded Gain (mu) 
 6.7
Effective Gain
5.6

Tube Power Output in Class A

21.6Watt 
Load Impedance (Ra)
2600 Ohm 
Grid resistor to ground
Max. 100kOhm 
.
520B Single Ended operating points
(This is just a selection from various points of the curve chart)

Plate Voltage

(Against Heater)

Grid Voltage

(Against Heater)

Plate Current (mA)
Plate Rp (Ohm)
Load (Ohm)

Plate Dissi-pation (Watt)

Power
Output (Watt)
2nd harm.
(dB)

Recommended Lundahl Transformer

400
-82
80
530
2800
32
13.2
30
LL1679-120mA
400
-81
100
530
2000
40
15.6
25
LL1679-120mA
400
-80
120
510
2000
48
18.7
25
LL1679-120mA
.
450
-95
80
580
3300
36
13.0
27
LL1620-100mA
450
-92
100
520
3600
45
14.3
31
LL1620-100mA
450
-91
110
520
3600
50
15.6
31
LL1620-100mA
450
-89
120
520
2600
54
21.5
24
LL1679-120mA
.
500
-106
90
620
3600
45
16.0
32
LL1620-100mA
500
-104
100
560
3600
50
17.5
32
LL1620-100mA
500
-102
110
560
2600
55
24.0
25
LL1679-120mA
.

Other operating points: For operating points, not given here, you can estimate the parameters by averaging between two rows of this table.

Output Power: Is specified at the tube, so transformer loss must be substracted. This is depending on the transformer choice and quality. Low Loss transformers have larger dimensions.

.

EML 520B Plate Curves

Download these curves as PTE file - What is that?

.

Mechanical Data 


UX4 BASE CONNECTIONS (UX4)

 
Size including Socket
(but excluding pins)

200 x 68 mm
7.5 x 2.7 Inch 

OCTAL BASE CONNECIONS

Pin 1+2: Heater1
Pin 6+7: Heater2
Pin 8: Center Tap (Cathode)
Pin3: Anode (Plate)
Pin5: Grid

Shipped weight 
for double box 
950 Gram 
.
 
    Note 1)  Hard metal has a higher melting point than classical nickel. Hard metal gives a more precise material shape, and does not change the shape when heated.  This ensures  reproducible tube parameters, and long term stability. Hard metals allow the most precise grid wire distance, and ensures better uniformity and linearity of the tube curves.
    Note 2)  Individual Test data, such as:  Matching Data, Grid Current, Vacuum, Filament Current, etc.,  are on the Certificate that comes with each individual Tube.  Each tube  is numbered, inside the bulb  with a metal Tag

    Note 3) This is a heavy power tube, and using it safely means avoid risks. The maximum conditions are destructive limits, which should not be reached even for a short moment. A "maximum possible" working point exists, but we do not specify it, because it is generally not a good idea to try this with any power device,both vacuum state or solid state, when you expect long life and reliability at the same time. We found that if we specify a "maximum" operating point, that in the end some users will try this out. So what we publish here, is the recommended working point, which gives best reliability, optimized sound and safe use at the same time.

    Note 4) Filament current has changed, from June 2005 to the value in this data sheet For tubes of older date, please refer to the filament current value as written on the certificate that is in the original tube box. Please inquire when this data got lost. 

    Note 5) When using a slow-start circuit for the filament, you may not apply plate voltage during that time.

    Note 6) Gold Grids is a word generally used for gold plated grids, so not gold wire grids. The grids we use are made of specially purified hard metal, which is then thermally gold plated. The advantage of gold plated grids is better temperature stability, and lower grid current if the tube gets very hot, and (within limits) it protects the tube from overheating damage and gives some self repairing effect after accidental overheating.


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