Not just an replacement, but an improvement!

Description / Application

For these tubes we use a very fine gold grid wire, with a gain of 21x for the 20A and 20B, and 32x for the 30B. It is recommended to use these tubes transformer or choke loaded. This is because you can use them at normal supply voltage then. Of course you can also use them resistor loaded, but then you need a supply voltage of 700V or more.

The 20A, 20B and 30A tubes are based on a very old principle, where high gain tubes have much wider plate distance. This is still the ultimate way to make a very linear DHT high gain tube. Miniaturization has always been the enemy of tube linearity, specially with DHT. The 20A/20B/30A will outdo any small size tube. We encourage you to check the tube curves of any miniature tube, like 6SN7, ECC88 or ECC82, and you will see this series presented here is much superior. However this results of larger dimension tubes is a higher working voltage. For this reason, tubes like this were not made any more after 1935, when miniaturization of tubes started to become more important. With the new production tubes we make today, miniaturization is no requirement. So for high gain tubes, we can now focus on lowest possible distortion. We build these tubes again the original way, with wide plates. Check plate pictures here. 

Distortion for small signal has been measured and is below 0,08% at 10 Volt output signal, at 400Volts plate voltage. For larger signal, distortion depends on the way the tube is used. Please note when one DHT triode is driving another, some part of the distortion of the second tube will be eliminated by the first tube. This even harmonics cancellation appears only with triodes, and they must be similar tubes, like drive a 300B with one of the tubes of this series. Since Triodes produce very low uneven harmonics, canceling the overall distortion this way, is an amazing application of the 20B or 30B tube. See also note 4)

For lowest possible mechanical noise with (any) high gain DHT pre-amp tube, use high quality tube sockets that do not pass the chassis vibrations to the tube. Chassis vibrations can come directly from the mains transformer, or by air from the loudspeaker. The best sockets for this are probably the Yamamoto Teflon, because Teflon is a flexible material. Use tight fitting Teflon tube dampers such as the Duende Criatura. They make the best damper for the EML tubes. They can be fit very nicely on the tube top, or one on the top and one on the bottom.

	Recommended SE Output transformer Specially designed by Lundhahl for this EML tube !
	For EML20B with Speaker Output, use LL2735B When using an 1:4 input transformer like LL1922, you can even build a One-Tube-Amplifier (OTA).

 

	Recommended Interstage transformer Specially designed by Lundhahl for this EML tube !
	For EML20A-Mesh or 20B with interstage, use LL2746. It can be used 1:1 or 1:2. With 1:2 interstage, and an additional 1:2 INPUT transformer, such as LL1570-XL you can build a complete driver, for tubes like 300B, 45 or 2A3. Thus bringing down noise, hum, and distortion to an incredible low level as not possible otherwise.

The EML 20A / 20B / 30A are  universal  and stabile tubes, combining high gain with low output impedance. The 20A-Mesh and 20B at a gain of 20,  there is no comparable directly heated tube, that offers such a low  plate impedance.  This makes it possible to use the 20B as an output tube. When using a step-up input  transformer, no additional tubes are needed , so it is possible to construct a complete HiFi amplifier with just one 20B tube. 

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

These tubes will often produce a blue glow on the glass.  This is because of the wider plate distance, and some electrons escape after collision. The fluorescent light pattern changes with the voltage or with the signal. These light effects are normal for this type of tube.  It must not be confused with gassy tubes, which  produce a purple-blue cloud  inside the plates.    High resolution image here.

• Gold plated, Wolfram Grid
• Center tapped filament
• Slow Start filaments, for best lifetime
• Hard metal Construction (Note1)
• 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.)

 

 

EML20A-Mesh

 

EML 20B
Side view

EML30A

High Resolution Pics

• Note 1)  Hard-metal filaments prevent filament breakage with DHT Tubes.  This material has a higher melting point than the classical nickel wires. Wolfram grids  allow the most precise grid wire distance, because wolfram is an extreme hard metal.   This ensures better grid  precision, which gives uniformity and better linearity at the low end of the tube curves
• 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)  Tube Curves:  Made on the The Sofia Curve tracer, with courtesy of AMR, Wisconsin, USA.
• Note 4) Theoretically, distortion of two tube stages in series, are eliminated provided both tubes produce only even harmonics, and produce the same percentage of even harmonics for each frequency at each signal level. This can be demonstrated indeed with two triodes of the same type, and the same electrical circuit, and the first stage has adjustable bias. You will find one specific bias point where the second harmonic is cancelled out almost completely, at one specific signal level. Since the third harmonic is of very low content with DHT triodes, what is left is a very small fraction of 4th harmonics, even so cancelled very much. The result will be zero 2nd harmonics, the normal level of 3rd harmonics, though very low with triodes anyway, much reduced 4th harmonics, whereas 5th harmonics and higher are not present e any more. In a practical set up, you can use the 20A or 30A for this, and choose the bias point of this tube for best results with the end stage tube chosen. Ultimate results will be achieved with 20A driving the 20B as output tube. This needs no further pre amp tube, so two tubes make the complete amplifier. However also with 20A combines with 300B or similar will make a perfect combination since 20A curves are exceptionally linear, with resemblance to 300B tubes. This method of distortion elimination method has first been described by Ratheiser, in the four-books tube manual. This is a "standard about tubes and circuits theory, only available in German language. Also this method is described in the book "Verstaerker in Roehrentechnik" by Rainer zur Linde ISBN nr: 3-928051-02-4, also only available in German. The Japanese designer SAKUMA has published a great variety of circuits, based on this principle, even driving 211 tubes with another 211.