Not just an replacement, but an improvement!

EML 300B-XLS
EML 300B-XLS V4

data sheet uploaded: 31-Mai-2014


Description

This tube has the classical grid construction and the tube curves of the 300B. It has the stronger plate construction and larger glass of the vintage 52B however. So in one tube we have combined the very best of two classical products.

Sound Character of the 300B-XLS tube

For use in Push Pull amplifiers, this is always the tube of choice, because this type of amplifier is hard on the tubes by definition. The 300B-XLS is made to deal with such conditions, and will allow the amplifier to play gently at low sound level, as well as reproduce higher sound level with the detail and precision you expect from a push pull amplifier.

For use in Single Ended amplifiers, the 300B-XLS is the best choice, since with those amplifiers good sound is coming from the right use of the tube, not over stressing the tube. The right use means, the tube should not be working at it's maximum electrical performance. Here we think the 300B-XLS is at it's right place, taking advantage of the higher electrical reserve this tube has. The 300B-XLS will reproduce the required loudness with more ease than the standard 300B. The result is a more transparent sound picture at low or medium volume, while at higher volume, the dynamics of the original recording will stay unaffected.

The 300B-XLS will bias in any amplifier the same way as the original WE300B. Sill it can be used in two ways if you want it.  These two modes are explained here.

1) You can replace any 300B with this tube.  Just plug it into any 300B amplifier, and the tube will set  itself exactly  to the original 300B working point. The EML 300B-XLS is is a very strong tube,  and it will develop the output power with more ease.  Specially for amplifiers that let the 300B tubes work very hard, the EML 300B-XLS is the right product  to choose. Any amplifier that is trying to get as much as possible power out of a normal 300B, will benefit from the 300B-XLS. Improved sound and longer lifetime will be the result.

2) Another   purpose of the EML 300B-XLS is to get more power,  than is possible with standard 300B tubes.  This can only be done when you have the possibility to adjust the settings of the amplifier.  If you increase the plate current of the tube ABOVE the standard 300B specifications, something very special will happen.  The tube  will now move to a part of the curves where it has a lower plate resistance. This is a specialty of the 300B-XLS. This will give a better damping factor of the bass and mid range loudspeakers, resulting in a more natural sound. Check our customer feedback section of the website!

All critical parts, like filaments, grids and plates are constructed of hard metal for the best reliability and reproducible quality. 

We have two versions for the heater: Normal heater, or Center Tapped heater.

With the center tapped tubes, we enter a 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, to this center tap there was never an electrical connection. So to the tube itself we had to make no changes. To the center tap of the heater, is now connected a wire, which becomes the third connection to 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.

Here is a link to Application Note 06, describing the center tapped tubes in general. Link here.

Recommended transformers

Single Ended: LL1623-90mA (Wire secondary for ALT B, C, D for : 4, 8, 16 Ohms in this order)

Single Ended: LL1623-120mA (Wire secondary for ALT B, C, D for : 4, 8, 16 Ohms in this order)

Single Ended: LL1664-80mA (Secondary 8 Ohms)

Complete list of recommendations here

 

Lifetime

With power tubes, the operating point has a large influence on the lifetime. In the below table, you will find some examples of good operating points, or you can choose your own from the tube curves. We can not express the lifetime in hours here, since this depends on too many factors. However we can divide this is three parts:

1) Highest lifetime will occur, when this tube is operated as a normal 300B, which means below 36 Watts. The superior cathodes of the 300B-XLS, the better plate cooling, better gettering, the double mica top, the gold grid, all together will protect this tube. This makes emission lasts much longer as you may expect from a standard 300B tube under the same conditions. Even so, a regular 300B is not even really recommended to use at 36 Watt, wheras with 300B-XLS this is no stress for the tube at all.

2) Very good lifetime will occur when you use the tube at or just below 43 Watt plate dissipation. Lifetime will be the same as with a standard 300B tube, or exceeded even in many cases.

3) We recommend to use the tube not above 55 Watt. When you stay below, the tube can be used problem free. You will notice the very good bias stability, and good lifetime, also at 55 Watt. The tube is made to last at this power level, and an acceptable lifetime will be reached.

We do not like to specify absolute maximum limits here, as there is no practical design use for this number. Instead of saying what is unsafe to do, we rather say what is safe to do. So this is found in the below tables. There is a realistic safety margin in those numbers, and short time Peak Plate Dissipation is safely above 55 Watt. See also Note6.

Features

  • Gold plated, Wolfram Grid
  • Soft rubber suspended tube base
  • Center tapped filament (Note5)
  • Slow Start filaments, for best lifetime
  • Double Mica tube top
  • 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 300B-XLS
Front -
Side


EML 300B-XLS V4
Octal Base.
This is a special version
(see the main text)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.
Filament Ratings (See note 5) 
 

Standard tube
300B-XLS
4Pin Socket (UX4)

Center Tapped
300B-XLS V4
8Pin Socket (Octal)
Filament Voltage (AC or DC)
5 Volt
2.5 - 0 - 2.5 Volt
Tolerance on filament voltage
5 %
5 %
Filament Current
1.5Amp
1.5Amp
.

EML-300-XLS Factory Test conditions

Plate Voltage
495V
Plate Current
100mA
Transconductance
6.2 mA/V
.

EML- 300B-XLS Maximum Conditions 

(Voltage and current not possible simultaneously - this is not a recommended operating point)

Plate Voltage 
550Volt 
Plate Current 
160mA
Power Output in Class A 
27Watt 
Grid resistor with Auto Bias
250k Ohm (note4)
Grid resistor with Fixed Bias
50k Ohm (note4)
.
300B-XLS Recommended Single Ended operating points
(This is just a selection, other choices are possible)
Plate Voltage
Grid Voltage
Plate Current (mA)
Plate Rp (Ohm)

Gain
(mu)

Load
(Ohm)

Plate Dissi-pation
(Watt)

Power
Output (Watt)
2nd harm.
(dB)
400
-74
60
720
3,8
3500
24
11
27
400
-74
80
720
3,6
2500
32
13
26
.
450
-100
60
780
5,2
4000

27

13
26
450
-100
60
780
5,3
5500
27
10
31
.
450
-98
73
720
4,1
2000
33
16
22
450
-98
73
720
4,5
3000
33
13
26
450
-98
73
720
4,9
4500
33
11

31

.
450
-97
80
700
4,2
2000
36
18
22
450
-97
80
700
4.6
3000
36
15
26
450
-97
80
700
4,9
4500
36
12
31
.
475
-97
90
670
4,7
1900
43
21
23
475
-97
90
670
5,1
2800
43
17
27
475
-97
90
670
5,5
4200
43
14
32
.
500
-98
110
630

5,4

1800
55
27
23
500
-98
110
630
5.9
2700
55
22
27
500
-98
110
630
6,3
4000
55
17
32

Choice of output transformer impedance: For each working point, a wide range of primary impedance is possible. When using a transformer of another value, you can estimate the output power and distortion by averaging between two rows of this table. Example: 500V, 110mA. Use of Lundahl LL1623-120mA (3k type). This will give you appr. 20 Watt @ 28dB 2nd harmonics. (28dB distance of signal to 2nd harmonics.

.

EML 300B-XLS Plate Curves

Download these curves as PTE file - What is that?
.

Mechanical Data


UX4 BASE CONNECTIONS (UX4)

Size including Socket
(but excluding pins)

175 x 63mm

OCTAL BASE CONNECIONS

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

Single Tube weight 
190 Grams 
Shipment weight for 
pair in gift box 
800 Grams

.

  • Note 1)  Hard-metal filaments prevent filament breakage with DHT Tubes.  This material has a higher melting point than the classical nickel wires. Hard metal plates have a more precise plate distance, and do not change shape when heated.  This ensures  reproducible tube parameters, and long term stability. Wolfram grids  allow the most precise grid wire distance, because wolfram is an extreme hard metal.   This ensures better uniformity and linearity at the low end 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)  Maximum specifications. These data are only to show the safety distance to the recommended operating point.   You can operate the tube at the maximum for a short period of time.  Exceeding the maximum, will decrease the lifetime  very rapidly. 
  • Note 4) We are recommending the same values as Western Electric in their 1950 Data sheet.
  • Note 5) A center tapped filament indeed has a real center tap in the middle, which much be constructed in a symmetrical way. Also read Application Note6 about this item
  • Note 6) Due to the strong emission, the special grids we use, and other quality factors, the EML 300B-XLS has a remarkable capability to self-repair if damaged by short time overload or other user mistakes. Of course this depends on the actual situation. Please contact us, if needed.

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