Not just an replacement, but an improvement!

EML 1605
EML 1605 V4

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This powerful triode is designed for amplifiers without compromise. This tube is not directly in the family of 300B tubes, but closely related. In few words, it is made for somewhat higher voltage, and it has somewhat higher gain.

The higher gain has a practical reason. The amplifier designer (or the ready amplifier) may already have a good working 300B drive circuit. Due to it's higher gain, the 1605 will produce the higher output signal, at the same input signal as a normal 300B driver stage will deliver. (This is maximum 60 Volt AC)

The higher output power is achieved by the higher plate voltage, keeping the plate current at the same level of tubes like 300B-XLS or 520B. The transformer manufacturer can easily make a good SE transformer for higher voltage, but has problems with much higher DC current. For this reason we have chosen the 1605 to be a somewhat higher voltage tube. Like this, it can be used with normally available SE transformers. All in all, this will make it convenient to make a new design with the 1605, which is inspired by existing 300B amplifiers. Finally, the lower bias voltage of the 1605 will help to make the power supply more efficient in case of auto bias amplifiers.

Even amplifiers that are designed for the 520B-V3 can be adapted for the 1605 in many cases with only minor changes. Provided the amplifier has enough plate voltage of appr 580V, all you need is adapt the tube bias, and check if the heater current can be supplied.

The high filament current, stands for excellent emission, which on a glance can be recognized by the beautiful linearity of the tube curves. On the long term, high filament current is the source for higher tube life as well.

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 an application note, for how to use the 1605-V4 (center tapped heater) Version.

Sound Character of the 1605 tube

When tubes are made larger and larger, such tubes often sound only good at high power. At low power, the sound becomes sterile, and the triode sound character gets lost. The 1605 is constructed to avoid this problem. It has wide, box-shaped plates, same as Marconi PX25, which tube is legendary for it's sweet, silky sound also at low power. This similarity gets also reflected by the tube curves of 1605, showing resemblance to PX25.

All together it can be said the sound of 1605 is in between 300B and PX25, though much higher power levels are possible.

Example of good transformer:

LL1623-120mA Wire secondary for ALT B, C, D for : 4, 8, 16 Ohms in this order
LL1623-220mA (Parallel Single Ended, two tubes).


  • Double Mica tube top
  • Gold plated, Wolfram Grid (Note6)
  • Soft rubber suspended tube base
  • Center tapped filament
  • Slow Start filaments, for best lifetime
  • 0.5 mm thick plates
  • 12 circular coolers (6 double plates)
  • Hard metal Construction (Note1)
  • Two side getters, one top 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, with white bottom.)

Detailed image
Side / Socket
Plate detail

Plate Curves

EML 1605
Standard UX4 Base

1605 V4
Octal Base.
This is a special version
(see the main text)

Important !
Read all notes at the bottom of this data sheet before installing this tube.
Filament Ratings (See note 5) 
Standard tube
Center Tapped
Filament Voltage (AC or DC)
= 5 Volt
= 5.0V with Balanced Heater.
( 2x 2.5V )
Tolerance on filament voltage
4 %
4 %
Filament Current
~ 2,1Amp
~ 2,1Amp
. .

Maximum Conditions
See also Note4.
(Not possible simultaneously) 

Plate Voltage 
Plate Current 
Power Output in Class A 
Grid resistor
max. 50kOhm 

Typical application
Recommended operating point
See also Note4.  

With auto bias or fixed bias

Plate Voltage 
Plate Dissipation 
Plate Current 
Grid Voltage 
Plate Impedance (Rp)


Amplification Factor 


Transconductance (Gm)


Power Output in Class A
Input Signal needed for full output Power
57Volt AC (RMS)
Load Impedance (Ra)
 2700-3600 Ohm
Recommended Transformer(s)
Lundahl LL1623-120mA
Grid resistor to ground
Max. 100kOhm 


alternate textPrint Version

EML1604 Mechanical Data

Size including Socket
(but excluding pins)

200 x 68 mm

Weight of one tube:
190 Gram 

Pin 1: Heater1
Pin 4: Heater2
Pin3: Anode (Plate)
Pin2: Grid

Standard UX4 Base

Size including Socket
(but excluding pins)

147 x 60 mm

Weight of one tube:
140 Gram

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

Special Octal Base, V4 Version
Shipment weight for 
pair in gift box: 800 Gram


    Note 1)  Hard metal has a higher melting point than classical nickel. Hard metal gives a more precise material shape, and does not change the shape when heated.  This ensures  reproducible tube parameters, and long term stability. Hard metals allow the most precise grid wire distance, and ensures better uniformity and linearity of the tube.

    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) This is a heavy power tube, and using it safely means avoid risks. The maximum conditions are destructive limits, which should not be reached even for a short moment. A "maximum possible" working point exists, but we do not specify it, because it is generally not a good idea to try this with any power device,both vacuum state or solid state. We found if we specify a "maximum" operating point, some users will try this out. What we publish here, is the recommended working point, which gives best reliability, optimized sound and safe use at the same time.

    Note 4) We specify 2% tolerance of the filament voltage, to indicate here that you should take great care in achieving exactly 5Volts. With DHT vintage tubes, you will often see only the filament tolerance unspecified. However this leads to a classical misunderstanding that in such a case one can choose 10% tolerance, which is not so for any DHT. NOS or new production.

    Note5) When using a slow-start circuit for the filament, you may not apply plate voltage during the slow start phase. Besides this tube has a slow-heat filament by itself, so a slow start electronic circuit has no advantage to use. This is so for all EML tubes. Also please read the guarantee conditions, about the use of electronic filament heater circuits.

    Note6) Gold Grids is a word generally used for gold plated grids, so not solid gold wire grids. The grids we use are made of specially purified hard metal, which is then thermally gold plated. The advantage of gold plated grids is better temperature stability, and lower grid current if the tube gets very hot, and (within limits) it protects the tube from overheating damage and gives some self repairing effect after accidental overheating.

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