EML AD1-UX4 Mesh


2A3 Mesh tubeThe EML AD1-mesh is a 15 Watt single Anode directly heater triode, electrically similar to 2A3, but AD1 works at 4Volt heaters. Though it is electrically not identical, any existing 2A3 circuit diagram can be used, provided you have the 4 Volt heater voltage available.

We have a version with the vintage 8pin Side socket, and with the 4Pin UX4 base.


8Pin High Resolution


4Pin High Resolution

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® website, to participate in the 5 years guarantee program.

Our Guarantee conditions

Register here for the 5years guarantee


An important feature of the EML AD1-Mesh, is the possibility to operate it at higher voltage than the historical tubes. Some historical tubes allowed the use above 250Volts, but not all. At higher Anode voltage, the AD1 turns into a tube with amazingly high efficiency, outdoing 2A3. However at the higher Anode voltage, it requires a higher impedance transformer.

  • Gray Wire Mesh Anodes, mounted on a hard metal frame for best stability.
  • Gold plates, Wolfram Grid
  • Soft rubber suspended tube base
  • Center tapped filament
  • Slow Start filaments, for best lifetime
  • Anode voltage maximum 400V
  • Can be used continuously at maximum Anode dissipation
  • Hard metal Construction (See Notes)
  • Two extra large getters
  • Hand blown Glass bulb
  • Anti-microphonic Anode- 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

Tube Sockets for AD1

The original P8 'side contact' socket was an historical Philips development. This socket had an interesting property, it pulls the tube inside the socket by itself. To make this work well, tube base dimensions, socket dimensions and shape of the socket springs has to be exact. We have to mention that new production chinese sockets are not so ideal. At EML, to build the AD1, we use Vintage tube bases from the 1930's, of which we have some stock. For the amplifier chassis, we recommend new made ceramic YAMAMOTO tube sockets, or NOS tubes sockets, both of which can be bought via the JACMUSIC company.

Sound Character of the AD1

The higher heater voltage of 4 Volts, is also the source of another sound. This effect is only so with directly heated tubes. The AD1 sounds less dominant, more silky than 2A3. It can be said that all 4Volts DHT from the 1930's 1940's have very high collector's value, much higher than 2.5 Volts tubes have ever achieved.

Let me quote Rainer zur Linde, who wrote several books in German language about historical tubes. Translated here in English: 'AD1 is the highlight of European DHT triodes, and also marks the end of the period of DHT tubes manufacturing'. Perhaps there is no better way to describe this tube.

Filament Ratings (See note 5)
Filament Voltage
4.0 Volt (AC or DC)
Tolerance on filament voltage
Filament Current
1,5 Ampere
Maximum Conditions
(Not possible simultaneously)
Anode Voltage
Anode Current
Anode Dissipation
15 Watt
Grid resistor
max. 300k Ohm
Typical Tube Parameters
measured @ Ua= 250V, Ia= 60mA
Anode Impedance (Rp)
670 Ohms
Amplification Factor
Transconductance (Gm)
6 mA/V
Recommended operating points
Class A (Single Ended) Auto Bias, with Cathode resistor
Anode Voltage
(to Cathode)
Supply voltage
(to Ground)
Anode Current
Anode Dissipation
Cathode Resistor (Rk)
750 Ohms
1200 Ohms
1679 Ohms
Control Grid Voltage
Load Impedance (Ra)
2500 Ohms
4220 Ohms
6300 Ohms
Recommended Lundahl Transformers
Power Output
4,5 Watt
5,3 Watt
5,8 Watt
These operating points are recommended in: 'Elektronenroehren, 2. Band, by H.BARKHAUSEN, 1928. This is one of the finest tube electronics books that I know, and several chapters are dedicated to the wonderful AD1 tube.


EML AD1-Mesh Anode Curves

Download these curves as PTE file - What is that?

Some recommended Lundahl transformers for classical working points. Possible with 2A3 and AD1.

Clicke here for complete list of recommendations.


Singe Ended.
LL1623-60mA. 11Hz @1.5dB

Alt.B = 4Ω
Alt.C = 8Ω
Alt.D = 16Ω

Singe Ended

LL1664-60mA 13Hz @1.5dB

8Ω Only

Parallel Singe Ended

Alt.C = 4Ω
Alt.D = 8Ω
Alt.E = 16Ω

Push Pull


Alt.B = 4Ω
Alt.C = 8Ω
Alt.D = 16Ω

Push Pull



Alt.B = 4Ω
Alt.C = 8Ω
Alt.D = 16Ω

Push Pull


(with optional 25% Cathode feedback winding)

Alt.B = 4Ω
Alt.C = 8Ω
Alt.D = 16Ω


Mechanical Data 

EML Logo is
on this side

bottom view

Size including Socket:

65 x 150mm  

EML Logo is
on this side
bottom view

Size including Socket:
(but excluding pins)

147 x 60 mm

Weight of one tube:
140 Gram

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

Single Tube weight 
110 Gram 
Shipment weight for 
pair in gift box
600 Gram



Note1) Gold Plated grids is a difficult to use technology, which reduces grid current to a minimum. Philips and Tungsram historical AD1 tubes suffer often from grid current and/or gas problems which may occur after the first 500hours of use. To the contrary, EML tubes have superb stability of the tube bias, and grid current much below 1uA.

Note2) 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

Note3) Serial filaments is a technology, found in all later types Emission Labs® tubes. We use a center tapped filament wire for this. The center tap is physically located on the mica Anode the bottom of the tube. By this we connect two filament wires are in series, and the connection point is the center tap. Since this center tap can not be connected to the outside of the tube, we call it a virtual center tap, but actually it really exists inside the tube, and ensures a perfect balancing of the emission of each individual filament wire. By this method we reduce tube hum to the lowest possible level.