Not just an replacement, but an improvement!

EML 5U4G-Mesh
EML 5Z3-Mesh

uploaded: 21-Jan-2016e -->


This data sheet applies for the 5Z3-Mesh and 5U4G-Mesh, which are electrically identical, only have different sockets. 5U4G-Mesh uses as Octal Socket socket, of which only five pins are used (and one of those is electrically not connected). 5Z3-Mesh uses an pour Pin UX4 socket.

This is a direct replacement for the historical 5U4G or 5Z3, but it can not replace 5U4GA or 5U4GB which are different tubes. See Note 4

Note that the Emission Labs tube is somewhat larger size than the original old tubes. Check below at mechanical data, for details. Like most NOS rectifiers, also the EML are Slow-Start tubes, protecting the power supply. The delay time for first function is 2 seconds, and the delay for full current is 7 seconds.

For ultra low ripple,  it is recommended to use the Lundahl LL1673 dual coil choke in low CMR configuration. In this configuration, there is virtually no field radiation from the choke. (See  link to circuit diagram, at the bottom of this page). 

  • Starting May 2011, we have included inside the tube glass a special element to stabilize the heater voltage. See also the pictures on the right. (or here) These elements at higher current, will increase their resistance, and help protect the heater against accidental over voltage.
  • Slow Start ( 2...7 seconds)
  • Filaments are series connected, for best symmetry of the two diodes inside.
  • Two extra large getters
  • Each tube is numbered, inside the bulb with a metal Tag
  • Two extra large getters, flashing the complete tube bottom
  • These tubes are shipped in a high quality box
  • Tube printing with real gold (metal), red color is burned into the glass
  • Starting May 2011, we have started to ship 5U4G-mesh with the new ceramic socket, with five pins. From Yamamoto, the Octal 8/5p Teflon socket is recommended. This is an octal socket, but has five pin holes only. It is specially used for this rectifier. When working with Octal sockets, you will find the Yamamoto an amazing top class product. For this rectifier you can take the special octal version with five holes only. Like this you can never put in a non-rectifier tube by mistake. You can also use normal octal sockets of course.
Filament Ratings
Filament Voltage
= 5 Volt (AC or DC)
Filament Current
~ 3.0 Ampere
Maximum ratings
NOT possible simultaneously
AC input voltage
DC output current
First capacitor, connected to plates


Total copper resistance of complete HV winding.

Not below 170 Ohms for curves 1...6

Not below 230 Ohms for curves 7...8

Mechanical Data

Bottom view

Tube Size including Socket:
165 x 60 mm
6.5 x 2.4 Inch

Filaments: 8 + 2
Plates: 4 + 6


Tube Size including Socket:
170 x 60 mm
6.7 x 2.4 Inch

Tube weight
130 Gram
Shipped weight for
double box with one pair
730 Gram

5U4G / 5Z3 MESH

Click for details

UX4 Base

UX4 Socket
(by Yamamoto)

Octal Base

5-Hole Octal Socket
(by Yamamoto)



Typical application

Left Chart for following values:

  • Capacitor input filter. Value chosen 10uF here
  • Transformer DC Resistance 170 Ohms for curves 1...6
  • Transformer DC Resistance 230 Ohms for curves 7...8

Right Chart for following values:

  • Choke input filter
  • Transformer DC Resistance= Uncritical
  • Capacitor value 16uf here.

How to use the Charts:

  • For HIGH VOLTAGE at LOW CURRENT, choose Capacitor input, such as 125mA / 620V DC is possible. (AC = 550-0-550)
  • For HIGH CURRENT at MEDIUM VOLTAGE, choose Choke input, such as 225mA / 440V DC is possible. (AC = 550-0-550)
  • Choose the requires DC Voltage on the Vertical axis
  • Choose the requires Output current on the Horizontal axis
  • Must be in white Zone
  • Take closest curves 1...8 for the transformer AC voltage, or estimate one curve in between.
  • Note right chart has quite horizontal lines at high DC current, meaning output voltage depends not much on actual DC current

These graphs are from the historical RCA data sheets. When designing new circuits yourself, be aware a tube rectifier is more difficult to use than a silicon diode. Very roughly a tube rectifier is like a silicon diode, with a resistor in series. You need to limit the peak value at any circumstance to prevent defects, and keep it as low as possible for best lifetime. Since peak current is difficult to measure, a more practical way is use graphs such as the one on the left here. All in the end, you will notice you need more than a quick glance on the data. You will always end up with some sort of de rating. Such as: At maximum voltage, you can not draw maximum current. At maximum current, you can not use the maximum first capacitor. Maximum tube life will not go together with maximum load conditions, etc. Mistakes come from now knowing how these compromises must be made, or copy circuits from the internet, made by others the same way.

The best for the tube, and for low hum field radiation is a choke loaded tube, so an L-C circuit. This will force DC current through the diodes, and AC current peaks are almost gone. It is quite hard to understand how this works. Also this is unpopular because it works at higher transformer voltage. An L-C circuit has the magic of load regulation too. So at higher current draw, the voltage will drop not very much. Still a choke costs more than just a capacitor. The first compromise is often to go for a capacitor loaded tube anyway, so a C-L-C circuit. However de rating is higher here. So look in the graph on the left, and you see that at 150mA at 650V is in the red zone, it is not allowed. At 650V you can only draw 80mA with curve #8 (550-0-550V transformer), or even only 28mA at curve #7. Note, this is official RCA information from the RCA tube manual 1954. You can download the 1954 and other manuals from

The following information is for a pure capacitor loaded tube, so even without a choke. For any other circuit, we much recommend you to have a look at the original RCA data sheets, winch content is too extended to quote it here, however this is the one and only reference for designs with a long tube life. Designs with mistake in it, will initially work. However, since a tubes have such a thing as lifetime, any design errors will result in white sparking, and/or reduced lifetime. Not just EML rectifiers, but any rectifier, new, NOS or used.

1) Find the required transformer voltage, when you know the required DC voltage, and DC Current.

For this, select the output DC Current on the horizontal axis, and the output DC voltage on the vertical axis. In the graph there is the green dot, where the arrow points at. This is an example for 175mA @ 350 Volts. From here move vertical up and down, and you find the lines of 350V~and 400V~. You have to estimate the line that would be at the indicated point. Here, that would be at 365V. The required transformer is 365-0-365V

2) At a specific transformer voltage, find the relation between output voltage and output current.

For this you see eight curves, numbered 1...8. The upper curve (#8) is for a transformer of 550-0-550V~. For instance at 150mA output current you find 600V= at the vertical axis. For transformer voltages that are in-between, you need to print this graph, and pencil in the required line.

Note, from the graph it can be seen, that curves 1...6 may be used at full 225mA maximum current. The curves 7 and 8 have some de rating, which means you can not use the full current of 225mA any more at this high DC voltage.


Please note it can not be the intention of a data sheet, to teach any user how to design a good circuit. So it is assumed you already know how to do this. However we try to tell some things here, that we know are sometimes forgotten. Also we encourage you to read the original old data sheets. from RCA, General Electric and Sylvania, and Telefunken.

1) Fuse Protection:

To protect the rectifier, a slow fuse must be used. If choke loaded, the fuse must be from the output of the DC voltage, to the rest of the circuit. If capacitor loaded, the fuse must be to the transformer center tap. (So where there is a wire to the transformer center tap, inside this wire must be a fuse inserted)

2) The ideal application of ANY rectifier tube, all brands, is Choke Loaded.

A choke loaded rectifier circuits will give better performance in many ways, however it's function is often misunderstood, and for this reason not often used. However we recommend a choke loaded circuits with first priority always.

Advantages of a choke loaded rectifier circuit, vs. capacitor loaded are following:

  • Transformer HV winding can be used up to specified maximum output power, instead of 66% de rated value for capacitor load. This is so for all transformers, any brand. Otherwise heavy mechanical hum may appear. In other words: A 100 Watt transformer winding may be loaded only with 66 Watt of capacitor loaded, or 100 Watt if choke loaded. Choke loaded circuits are almost a resistive load for the transformer, whereas capacitor loaded circuits cause impulsive load (with rattling noise).
  • Longest lifetime of the rectifier
  • Less AC field radiation from the wiring
  • Very lower internal resistance of the output voltage, when above 1/3 of maximum output current. This will make the DC voltage independent of the current drawn, within 10%. Capacitor loaded rectifier circuits provide no load regulation, and drop the output voltage rapidly at higher current.
  • No need to deal with transformer windings resistance

3) If Capacitor loaded, you must have a minimum required copper resistance of the transformer winding.

This is an old design rule, obligatory for any 5U4G, EML or other brand. If capacitor loaded, the first capacitor must be chosen at or below the maximum value in this data sheet. At EML we adapted to the same values from old data sheets. So there will be no doubt about those values. The minimum resistance is specified for the complete winding. (So not measured from the center tap). In case you use a transformer with too low copper resistance, you need to add one series resistors in each HV winding connection of the transformer. Then, with those two resistors in series, you re-measure the transformer winding, and the result must be as follows:

Raa, value, for Curves 1...6: minimum 170 Ohms
Raa, value, for Curves 7...8: minimum 230 Ohms

If you ignore this design rule, tube damage will result. Also in many "professional" amplifiers, this design rule is not used by designers who do not read the historical data sheets Tube damage can result as a white spark inside the tube at switch on, filament material can chip off, or the tube life will be much reduced. With most amplifiers, the transformer winding is directly connected to the tube socket, and no protective series resistors are used. In most cases, the transformer resistance can be conveniently measured by a specialist, directly at the tube socket, when the rectifier tube is removed first.

4) Never operate the tube in the red area of the graph, above.

Note the graph has a white and a red (pink) area. Operation in the red area is strictly forbidden. Going to the limits is possible, but maximum tube life will not result from this. The "70%" limit for long-life operation applies also here.

Note, when studying the graph, you will see a dotted line, on the right upper side. It looks like a corner of the graph is cut off here. This cut off piece will be larger when the first capacitor is larger. So now, it is specified for a first capacitor of 10uF in this graph. The best way to prevent problems, is not the maximum value capacitors, and use simply a bit higher transformer voltage and larger chokes to get the required result. This will not give less efficiency of the rectifier circuit ! It will however make any type of rectifier tube last longer. Even the opposite effect can be seen, when people over-rate the first capacitor in an attempt to get lowest possible hum. In several cases, over-rating the capacitor will even increase the total hum of the amplifier. Elementary design rules say, you stabilize a high voltage with a large choke, and low voltage with a large capacitor. With maximum value capacitors, the capacitor charge pulses get extremely high, causing hum field radiation into the pre-amplifier wiring and tubes. These charge pulses have a kind of "bad sounding" wave shape, and smallest hum field radiation from this, can become audible if strayed into the pre-amp circuit anywhere. Two design notes for this are at the end of this data sheet. When designing your own circuit, you should really read those notes.


  • Note 2) To prevent large charge current peaks, the first capacitor (C1) should NOT be larger than 40uF. If the input capacitor is too large, this will result in heavy AC charge current through this capacitor. This is not good for the rectifier tube, and also not for the capacitor lifetime. The AC capacitor current peaks may cause hum radiation into the preamplifier. With the given C-L-C values in table, the rectifier circuit will work best. For filtering, with oversized components, you will have best results by increasing the choke. Do not oversize capacitor C1, this may increase hum. You can choose the choke large as you want. This will have better results with high voltage rectification.
  • Note 3) Rectifier tubes may under no circumstance carry larger current peaks as what they are designed for. The current peaks are mainly a function of: power supply DC load, first capacitor and transformer copper resistance. The copper resistance for 5U4G and 5Z3 may not be smaller than 170 Ohms. This is very important to check, and too low copper resistance may damage the rectifier, no matter what brand or construction. Use a small series resistor if the copper resistance of the used transformer is too low. If you scroll further down this data sheet., there is a link to a table with historical information about this, for several rectifier types, not only 5U4G.
  • Note 4) There is common misunderstanding that 5U4G and 5U4GB is the same. 5U4GB is a version, with lower internal resistance and higher peak current is allowed. The GB version is not the same tube as the G Version. Replacing 5U4G with 5U4GB may result in higher rectified voltage, so should never be done. Replacing 5U4GB with 5U4G may result in lower rectified voltage, and may result in damage of the 5U4G rectifier.
  • Note 5) For those who do computer simulations, the plate current of 5U4G can be found by Child-Langmuir's Law. This results in the formula Ip=K*Vp^1.5 You can enter this in programs and draw a plate curve. The number K is the Diode Perveance, the value is in Amps per Volt, that tells nicely what that means. That you have to find experimental with new tubes. It was found for new 5U4G as 0.000777


    Design note-1

    Design note-2

    Circuit 1: This is the most commonly used. What is not so nice about this circuit, will get clearer when you understand the benefits of the other circuits here.
    Circuit 2: Added here is a bleeder resistor, a ground connection point, and if needed an external windings resistance. The ground connection point prevents any faulty ground path. This is called "star" grounding.
    Circuit 3: This avoids the rectified DC current flows through the transformer heater winding. This will reduce Transformer hum. However circuit #4 is more simplified and will do the same.
    Circuit 4: This circuit refers the Choke AC and DC electrical field to ground, where they can cause less problems. Also the ground path for the first capacitor is now forced in a correct way, same as in circuit 3.

    Circuit 5: This is how to connect a double coil Choke, such as the Lundahl LL1673 or similar products. Beware the polarity of the connections. (the dots in the circuit diagram here). The importance of this circuit is very high. We have complete inductive separation of the transformer from the amplifier. Definitely, the transformer capacitance from primary to secondary can not inject an AC hum current into the amplifier any more.

    Bleeder Resistor: This is to empty all capacitors after power off. Using no bleeder resistor is not only dangerous, it is also one of the reasons for a sparking rectifier. Make sure the resistor discharges all capacitors to less than 40V in one minute. Do not mount in directly on a capacitor, if the resistor gets too hot. Electrolytic Capacitors must be kept cool.

    Windings resistance. The special knowledge of tube transformer making has gone lost. Each rectifier requires a certain MINIMUM windings resistance, or the tube will have low lifetime, or even show a white spark. Transformer Raa is measured between the tube Anodes. In many cases the value is too low. This major design error can be fixed by adding an external resistor as shown. This resistor has half the value of the total Raa required. If a tube needs Raa of 250Ω

    Ohms, and you measure 100Ω only, there is 150Ω missing. You need to add 0.5 x 150Ω externally, in series with the center tap. Ignoring this, will lead to reduced tube life, or early failures.



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