Not just a replacement, but an improvement!

EML 300B

Uploaded: 27-Feb-2016e -->


Description

With this tube we have taken the legendary 300B in production. All critical parts, like grids and plates are constructed of hard metal for higher reliability and reproducible quality. This tube is a direct replacement for the WE300B, and features a center tapped filament as well. (See Note6)

Sound Character of the 300B tube

For the sound character of the EML 300B, we mainly refer to the original NOS 300B, as made until 1988 by Western Electric. We regard this tube the reference. Generally speaking, the 300B has not such extreme high requirements to the speaker system as for instance tubes like the 45 will have. This makes the 300B sound more predictable, and harmonic distortion is the most important parameter. The original WE Data sheet (full version) gives several pages with distortion tables, which speak clearer language than the text here. The result is though, in practical situations, a 300B tube will produce small but noticeable distortion depending on amplifier design and load conditions. Due to the lack of odd harmonics, this distortion is often experienced as sharpness, less transparency and imprecise bass. Also there is no amplifier in the world that can combine highest output power with lowest distortion. So the compromise is either on distortion or on output power. So far this is general for all brands 300B. At EML we have contributed to the best 300B sound, by extremely low hum and distortion of our tubes. This was done by a new filament construction. They are featuring a real, physical filament center tap, positioned far outside of the plates, but inside the glass bulb. The result is, we reduce the hum level of our tubes, even below that of many NOS tubes. The gold grid we use, is giving most stabile bias also under harder conditions, and good matching between two tubes of a pair is guaranteed like this over time.

In speaker systems where lower power is needed, you will see the EML300B has a great ability to play gently at low volume as well, at lowest noise and hum level, award the low power use with a clean and dry bass, and highest transparency. The glass bulb size has been reduced, to minimize acoustic feedback. The tube base is attached with soft rubber compound, minimizing mechanical chassis noise coming inside the tube.

Example of good transformer:

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

Features

  • Gold plated Grid. (Note 8)
  • Center tapped filament
  • Soft rubber suspended tube base
  • 4 circular cooling plates
  • Hard metal Construction (Note 1)
  • 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.)


300B

Detailed image

.
300B Filament Ratings
Filament Voltage
= 5 Volt (AC or DC)
Tolerance on filament voltage
4%
Filament Current
~ 1.3 Ampere
.
300B Maximum Conditions
Not possible as operating point
Plate Voltage
450Volt
Plate Current
100mA
Power Output in Class A 
17.8 Watt 
Plate Dissipation
40Watt (note5)
Grid resistor with Auto Bias
250k Ohm (note4)
Grid resistor with Fixed Bias
50k Ohm (note4)
.

300B Factory Test conditions

Plate Voltage
300V
Plate Dissipation
17Watt
Plate Current
56mA
Grid Voltage
-58Volt
Plate Impedance
700 Ohm
Amplification Factor
3,9
Transconductance
5.6 mA/V
.
300B Recommended Single Ended operating points
(This is just a selection, other choices are possible. The Line Nr. you see in this table ist just for communication)
Line

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)
1
350
-74
60
720
2000
21
10.2
21
2
350
-74
60
720
3000
21
8.3
26
3
350
-74
60
720
4000
21
7.0
30
4
350
-71
80
640
2200
28
9.6
26
.
5
400
-74
60
720
3500
24
10.5
26
6
400
-74
80
720
2500
32
12.5
25
.
7
450
-100
60
780
4000

27

12.5
26
8
450
-100
60
780
5500
27
10.0
30
9
450
-98
73
720
2000
33
16.2
21
10
450
-98
73
720
3000
33
13.2
25
11
450
-98
73
720
4500
33
10.5

30

12
450
-97
80
700
2000
36*
17.8
21
13
450
-97
80
700
3000
36*
14.6
26
14
450
-97
80
700
4500
36*
11.5
31

* Lifetime gets less at 36 Watt dissipation, regardless of the tube brand. For best lifetime, it is recommended to stay below 33 Watt. For highest output power and no compromise with lifetime or distortion, it recommended to choose the 300B-XLS.

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: 450V, 60mA. Use of Lundahl LL1679-70mA (4k5 type). This will give you appr. 11.5 Watt @ 27dB 2nd harmonics. (28dB distance of signal to 2nd harmonics.

.

EML 300B Plate Curves

alternate text300B Plate Curves Print Version

Download these curves as PTE file - What is that?

300B Mechanical Data

Size including Socket
(but excluding pins)

148 x 65 mm

Single Tube weight 
145 Gram
Shipment weight for 
pair in gift box 
840 Gram
.
  • Note 1) Hard-metals can be used in electron tubes, though these are more difficult to use, and more costly than the classical nickel. Hard metal plates have a more precise plate distance, and do not change shape when heated, or at mechanical shock. 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. Best grid geometry ensures 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 is on the outside of the tube box. Each tube is numbered from the inside, with a metal Tag
  • Note 3) Plate Curves: Made with the Sofia Digital Curve tracer. Plate curves with courtesy of AMR
  • Note 4) We are recommending the same values as Western Electric in their 1950 Data sheet.
  • Note 5) The Western Electric 1950 Data sheet. says 36 Watt maximum dissipation. Later data sheets say 40 Watt. Though 40 Watt is possible, this is a peak value only, and no normal working point. When you intent to get the "maximum" out of a 300B, and operate this tube at the limits of safe operation, it is a better idea to use the 300B-XLS in such a case.
  • Note 6. Some manufacturers claim to be the only one with a center tapped filament, but this is not longer true. At EML we build since several years now all triodes center tapped, not only the the 300B.
  • Note 7) Don't experiment with lower filament voltage, and expect better lifetime. If it was that easy, we would make them like this ourselves. The specified filament voltage is the one for best lifetime.
  • Note 8) Gold plated grids have a few advantages. Amongst other this will give better bias stability of the tube, some protection against accidental overload, and better linearity of tube curves.

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