Preliminary 12B Data Sheet


2A3 Mesh tube

The 12B tube is in the family of 20A, 20B, 30B. It can be used as a medium gain driver tube, or as an output tube for smaller amplifiers, as well as head phone applications. With the appropriate circuitry (see application note) it can also be used as a line output tube.

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  • Very wide Anode Distance for a nice glow picture.
  • Excellent linearity combined with medium gain.

Sound Character of the EML 12B

At smaller signal level, tubes with low gain often develop a sterile sound. Such tubes are not designed for small signal. Better is to use higher gain tubes for small signal, and medium gain tubes as a driver. As a rule of thumb, a tube like 300B requires 60 Volt AC signal on the grid. The gain of the 12B is a factor 12 to 14.5 depending on the load. If choke loaded, the gain will be 14.5. If speaker loaded, the gain will be around 12 to 13.

As a driver tube for 300B, the 12B would typically be operated choke loaded, or transformer loaded, and requires appr 4V AC signal on the grid. This can be achieved conveniently with a step up input transformer with a factor 1 : 3, resulting in an input sensitivity of 1.3 Volt. In this way, there is no more need for a pre amplifier tube, which would be only a source for hum and noise, because signal would be very low. Whereas an input transformer can supply a gain of factor 2...4 cost effective, and virtualy no noise or microphonics, and even prevents cable hum to enter the amplifier via the input.

In case even higher input sensitivity is needed, the 12B can also drive an inter stage transformer with a step up factor of 1:2 with ease.

The lower output resistance makes this tube uncritical in the choice of output transformers, yet keeping the gain around 12....14 depending on the application. This higher gain will develop the typical sound, of tubes like PX25 or RE604, which have a silky and non dominant sound.

A very nice application is also in a head phone amplifier, because relatively low output signal is needed, yet at lowest possible hum, noise and microphonics. Here, the use principle is another. Such amplifiers should be designed for having more amplification as strictly needed, and then the signal level is attenuated on purpose at the output. This attenuation will also attenuate any noise from the tube, making the amplifier very low noise. Yet, even at low signal on the head phone, still the output signal on the 12B is not extremely low, allowing the triode sound to develop. The attenuation is made be the output transformer.



EML12B Filament Ratings
Filament Voltage
5 Volt DC
Tolerance on filament voltage
Important: See Notes.
+/- 4%
Filament Current
1.3 .. 1.4 A


EML12B Maximum Conditions
not possible simultaneously
Anode Voltage
Anode Current
Anode Dissipation Continuous

Highest possible Grid to ground resistor, Single Ended.


Highest possible Grid to ground resistor, Push-Pull.



EML12B Factory Test conditions
Anode Voltage
Anode Current
Amplification Factor
5.6 mA/V
Control Grid Voltage


EML12B Electrode Capacity


Filament measured with one end
connected, other end open.


EML12B Recommended Single Ended operating points.
Other choices are possible.

Anode (V)
vs. Heater



vs. Heater

Anode Current (ma) Anode Rp (Ohm)









2nd harm.

Curves of 2A3 tube

EML 12B tube curves

12B Anode Curves Print Version (full size pdf)

Download these curves as PTE file

What is a PTE file?


SPICE Parameters

Link here


Some recommended Lundahl transformers

For EML12B with Speaker Output, use LL2735B

For Head Phone Applications use LL2765

1:2 Inter stage transformer: LL2746

A good 1:4 input transformer is LL1922



EML 12B Mechanical Data

Size including Socket
(but excluding pins)

148 x 65 mm

Pin 1: Heater1
Pin 4: Heater2
Pin2: Anode
Pin3: Grid

Weight of one tube:
145 Gram

Shipment weight for pair in gift box:
840 Gram

UX4 Base



  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 Anodes have a more precise Anode 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.
  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
  3. Average Plate Characteristics: Made with the Sofia Curve tracer.
  4. Do not experiment with lower filament voltage, to expect better lifetime. If it was that easy, we would make the tubes like this ourselves. The specified filament voltage is the one for best lifetime.
  5. Gold Plated grids have a few advantages, such as increased bias stability, some protection against accidental overload, and better linearity of tube curves.
  6. Heater voltage is always defined at the tubes pins itself. There may be some voltage drop along the wires, and tube contacts as well. So voltage measured at the tube socket wiring should ideally be 5.1V.