Data Sheet

12B, 20A, 20B, 20B-V4, 30A

Description

2A3 Mesh tubeFor these tubes we use a very fine gold grid wire, to achieve higher gain. If not used as output tube, It is recommended to use these tubes choke loaded, and they can be used at normal supply voltage then. If used resistor loaded, they can be used on a supply voltage of 600V or more.

This series of tubes are made for higher gain. The mechanical dimension is the same as our 300B series. Miniaturization of tubes, as you can quickly seen, is always on the cost of distortion, and also such miniaturized tube have a tendency to work on lower voltage. All of which makes such miniaturized tubes not ideal for larger signal. This is where our tubes step in. So if size is not a problem, these tubes offer a combination of low distortion, high gain, yet at high signal as well, which is not found with tubes made before.

Gain of 12B is appr 14x, 20A/20B is appr. 20x, and 30A is appr. 30x. Depending on the tube type, they can be used as driver tube, pre-Amp Output, Head Phone, or low output speaker amplifier.

A unique application is possible with 20B, called the OTA amplifier. Such a complete amplifier works only one tube: The 20B. Thus providing a speaker output, and a normal signal input. The method here, is to use an input transformer with voltage amplification if appr 4x. Together with the gain of 20x of the 20B, this provides the gain needed.

All of these applications are combining high signal level with high gain and low impedance at the same time.

As a driver tube, when using a Anode resistor, 20A an 20B can work with high voltage circuits for instance for an 845 tube, from a high power supply voltage of around 800 Volt. For supply voltages around 400Volt the use of an Anode choke is recommended to have sufficient Anode voltage remaining over the tube.

Some possible applications
 
ANODE TYPE
 
30A
White Powdered One single tube for the first stage and driver
20A
Mesh Driver tube, or output tube
20B
Black Powdered Driver tube, head phone, output tube, OTA (One Tube Amplifier)
20B-V4
Black Powdered Pre-Amp, driver tube, head phone, output tube.
12B
Black Powdered Very good combination of medium gain, and higher speaker output signal possible. Yet also a perfect driver tube.


Guarantee program for first owner.

At EML we have the normal guarantee. In addition to that, the first owner can register the tube within 4 weeks after receival, at the Emission Labs ® web site, to participate in the 5 years guarantee program.

Our Guarantee conditions


Register here for the 5years guarantee

Features

Sound Character of the EML 12B, 20A, 20B, 30A Series

20A/20B vs 30A

The 30A tube is just made for higher gain, and less gain of it's driver stage is needed. However output impedance of 30A is accordingly higher, and the design must be made with more care. Whereas the lower output impedance of the 20A /20B Series is generally easier to work with. (Here is a measurement, showing 60dB distance from 2nd to 3rd harmonics, using the 30A tube. This graph is for the tube + transformer together).

The new 20B-V4 tube

We recommend this tube for new designs, because it is upwards compatible to the classical 20B, but offers the advantage of the center tapped heater. By adding a center tap connection to the filament, we get a real cathode connection, for a simpler circuit, yet with better performance. This requires an socket with more than 5 electrical connections pins, so we choose for the Octal socket.

With the Balanced Heater, we enter a new field of applications. When biasing a DHT tube, there is no cathode to connect something to. The cathode connection must be artificially constructed, either by two resistors, or by a center tap on the heater transformer. Both these methods are a compromise to the signal path, and this compromise is now eliminated by the V4 version.

It must be said, the V4 is a beautiful tube, which fulfills the needs of designers, the best possible way. Link to Application Note AN-6 about balanced (center tapped) heater.

Recommended SE Output transformers

Specially designed by Per Lundhal for this EML tube !

For EML20B with Speaker Output, use LL2735B

When using an 1:4 input transformer you can even build a One-Tube-Amplifier (OTA). We have a programmable (1...4x) gain PCB for this purpose, using LL1544A. .

Some Examples of OTA amplifiers Pic1 - Pic2

For 12B, 20A-Mesh or 20B, we recommend Lundahl inter stage LL2746. It can be used 1:1 or 1:2.

With this 1:2 inter stage, and an additional 1:2 INPUT transformer this will be a one-tube driver system, for tubes like 300B, 45 or 2A3. Thus bringing down noise, hum, and distortion to an incredible low level as not possible otherwise. We have a programmable (1...4x) gain PCB for this purpose, using LL1544A

Filament Ratings
Standard tube
12B, 20A, 20B, 30A
4Pin Socket (UX4)
Center Tapped
20B-V4
8Pin Socket (Octal)
DC voltage recommended
= 5 Volt
= 2.5 - 0 - 2.5 Volt
Tolerance on filament voltage
5 %
5 %
Filament Current
~ 1,4Amp
~ 1,4Amp
.
Maximum Conditions
(See Notes)
EML
12B
EML
20AM
EML
20B
EML
30A
Anode Voltage
500V
450V
550V
500V
Anode Current
60mA
40mA
60mA
40mA
Continuous Anode Dissipation
25Watt
11Watt
25Watt
11Watt
Power Output in Class A
6Watt
3,6Watt
5Watt
3Watt
Grid resistor
below 470k
below 470k
below 470k
below 470k
.
Typical Data
EML
12B
EML
20AM
EML
20B
EML
30A
Anode Voltage
390V
400V
420V
400V
Anode Current
40mA
25mA
42mA
25mA
Anode Impedance (Rp)
2k9
4k5
3k3
6k2
Amplification Factor
13.5
22,5
20
32
Transconductance
5.6 mA/V
5mA/V
5,9mA/V
5,2mA/V
Load Impedance (Ra)
8..16k
12..20k
11...19k
19k
Control Grid Voltage
(actual voltage may differ, depending on test data)
-16V
.
Recommended use
EML-12B
EML
20AM
EML-20B
Low bias
EML-20B
Med Bias
EML-20B
Max Bias
EML-30A
Anode Voltage
390V
380V
380V
420V
500V
400V
Anode Dissipation
16Watt
9 Watt
12Watt
18Watt
25Watt
9Watt
Anode Current
40mA
24mA
32mA
43mA
50mA
22mA
Control Grid Voltage.
See Notes
-16V
-10
-9V
-7,5V
-10V
-3V

30A Some operating points
Anode Voltage
Control Grid Voltage
See
Notes
Anode Current (mA)
Trans-
Conduc-
tance
(mA)
Anode Rp (Ohm)
Gain
(mu)
300
-3
10
4.6
8k
36
300
-2
15
5.3
6k6
35
300
-1
20
5.5
5k9
33
.
360
-5
10
4.4
8k
36
360
-3.8
15
5.1
6k9
35
360
-2.8
20
5.7
6k
34
360
-2
25
6.2
5k6
34
360
-1.1
30
6.6
5k1
34
.
420
-6,7
10
4.3
8k5
36
420
-5.6
15
5.0
7k
35
420
-4.6
20
5.5
6k
33
.
480
-8.6
10
4.1
9k3
38
480
-7.5
15
4.9
7k2
35
480
-6.5
20
5.5
6k3
35
.

Mechanical Data

UX4 BASE CONNECTIONS (UX4)

Size including Socket
(but excluding pins)

155 x 58 mm
6.1 x 2.3 Inch

Single Tube weight:
145 Gram

Shipment weight for pair in gift box:
700 Gram

V4-VERSION
OCTAL BASE CONNECIONS

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

Notes.