Description

The 520B is a long Anode Version of the older 52B, with many technical improvements added. The EML520B is a state of the art product, in the family of the 300B tubes. This powerful tube is recommended for new designs. The 520B has the same outside dimensions as the '845' tube, but longer Anodes. All critical parts, like filaments, grids and Anodes are constructed of hard metal for higher reliability and reproducible quality. Note the relation between the tube base, and and the glass bulb. Then compare this with our 300B. This gives you some idea of this tube's size. High Resolution

Guarantee program for first owner.

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, which is additional to the legal obligations of the seller.

Our Guarantee conditions

Register here for the 5years guarantee

Features

• Gold Plated Grid (See Notes)
• Soft rubber suspended tube base
• Hard metal Construction (See Notes)
• 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
• Gold Plated pins,black ceramic socket.(White bottom.)

Sound Character and use of the EML 520B

1. Use as improved 300B tube

Though this is no drop-in replacement for 300B, it is possible to replace a 300B with this tube, provided some things which must be checked. Care needs to be taken to have the right bias, and also it needs to be sure the heater supply will still do 5V at the higher current of the 520B. (2.1 Ampere vs 1.3 Ampere of 300B). With some knowledge of electronics, these can be used as ultimate upgrades for 300B tubes.

One of the best things of the 520B is the lower Anode resistance (480 Ohms of 520B vs 700 Ohms of the 300B). This will lead to higher efficiency of the amplifier, and a more output signal, even at the SAME bias settings. Moreover the signal will be less distorted at higher volume, The lower Anode impedance will also give better control of the BASS speaker chassis, since the damping factor increases with 25% compared to standard 300B. This will not give so much louder bass, but more natural sounding bass. This can be done with existing 300B amplifiers, provided the technical checks, described in the previous text.

2. Use as large high power 300B tube

In cases where a significant higher bias of the tube is possible, an undistorted 18....20Watt Single Ended power can be supplied by the 520B tube with great ease, or up to 24 Watt as a maximum. This requires dedicated amplifier design.

3. Use as Push Pull tube

The 520B-V3 is very well suited for Push Pull applications also, since the higher peak emission (vs 300B) will ensure much longer lifetime for the 520B. Occasional overload of a push pull amplifiers is sometimes hard to prevent, if the user wants the maximum out of it. Other than with SE amplifiers, the power dissipation of a Push Pull amplifier is very dependant of the maximum output signal, and rises even sharply if driven into distortion. Unlike the previous models (called 52B), the 520B is not immediately taking damage of accidental abuse. Of course we can not specify how far you can exceed the maximum, but the thermal capacitance of the anode is very large, and this is the best protection against accidental (short time) overload. Another protection is the special grid, which will not develop grid current after occasional overload of the Push Pull stage. Last but not least we use a special anode composite, which allows very high dissipation. We do not specify how much, but there is considerable reserve in the specifications of the 520B, making it a very reliable tube despite it's hard use condition.

We have three versions for the heater:

1. The older 6.5 Volts heater. (Version V2)
2. The newer 5Volts heater. (Version V3)
3. The Cathode Tapped (balanced) 5 Volts heater with Octal base. (Version V4)

With the Cathode Tapped tubes, we enter a new field of applications. This has not been done before with Audio tubes. When biasing a normal DHT tube, like 300B or any other, there is no cathode to connect something to. The cathode must be artificially constructed, by a resistor network, which is a small compromise. Reason is, inevitably, not just the tube's DC current, but also the complete AC signal current must pass through those resistors, which has some obvious disadvantages. Provided the heater wires are all serialized, we may tap this in the center, and voila: We have our cathode back again. Moreover this behaves like a real cathode. So the V4-tube has an Anode, a Grid, and a Cathode. The centering resistors are no longer needed. For the heater we have connections H1 and H2, and all we need, is a floating 5V connected to it. We took the opportunity, to connect H1 and H2 each with two contacts, to have lower contact resistance. So indeed, we end up with a real, 3-connection triode, and a 5V 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, it is still possible, if you change your mind, connect a V4-tube, the classic way, like any 300B or 520B-V3. In that case, disconnect the Cathode Tap, and connect the remaining 4 wires like any regular Directly Heated tube.

Here is an application note, for how to use the V4 (Cathode Tapped heater) Version.

Please read all notes at the bottom of this data sheet before installing this tube.

Some suggestions for Auto Bias

Notes

1. This is a heavy power tube, and using it safely means avoid risks. The maximum conditions can be destructive limits, if exceeded continuously. A 'maximum possible' working point exists, but we do not specify it, because it is generally not a good idea to try this out, with any power device, as well as vacuum or solid state. So what we publish here, are recommended working points, for good reliability, optimized sound and safe use.
2. 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. Gold Grids is a word generally used for gold Plated grids, so not 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.
3. Filament current has changed, from June 2005 to the value in this data sheet For tubes of older date, please refer to the filament current value as written on the certificate that is in the original tube box. Please inquire when this data got lost.
4. When using a slow-start circuit for the filament, it is definitely not allowed to apply Anode voltage during that time. This voids the guarantee on our tubes. 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. 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
6. The curves for this tube are plotted, with AC heating. For DC heating, all grid voltages shift 2.5 Volts.
7. 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.