Not just a replacement, but an improvement!

EML 5U4G-Mesh
EML 5Z3-Mesh


Please note, Emission Labs ®was the first company to introduce a mesh version the 5U4G in the year 2006. Also, we were the first company no re introduce the 5Z4 in 2007.


This data sheet applies for the 5Z3-Mesh and 5U4G-Mesh, which are electrically identical, apart from the 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 rectifiers are Slow-Start tubes, protecting the power supply to some degree. 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)
Tolerance on filament voltage
Filament Current 
3 Ampere 
Maximum ratings
NOT possible simultaneously
AC input voltage
DC output current
225mA Capacitor loaded
265mA Choke loaded
First capacitor, connected to Anodes


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
Anodes: 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 Capacitor loaded tube,
with these 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

Left Chart for following Choke loaded tube,
with these values:

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

About these Charts:

These charts are graphical design tools, saving the trouble of calculations.

Both charts show some degree of derating, meaning you can not have maximum current and maximum voltage at the same time. As the choke loaded circuit is not so hard on the tubes, you will see derating is less at very high current. So the maximum of 265mA can be used up to 350V DC output. This is definitely not possible with a capacitor loaded circuit. Though capacitor loaded circuits perform good at low to medium current, like at 100mA you can get 600V, where choke loaded will only do 470...540V depending on the choke inductance. This is only from the view of convenient use. From the view of good tube life and smallest hum field radiation, choke loaded is preferred, unless you work at very low current, like below 75mA.

From the right choke loaded chart it can be seen, the maximum current of 265 can be used to generate 350Volt DC, whereas the capacitor loaded circuit at 350V can only so 230mA. Yet when generating 480VDC, the limit is 150mA only of choke loaded, or 200mA capacitor loaded. It pays off to check, if you can fulfil the needs with a choke loaded circuit, and if yes, this would be the better circuit to take. So both circuits can do 480V at 150mA, and choke loaded will sure do this at less disturbance to sensitive circuits near by.

How to use these Charts:

  • Choose the required DC Voltage on the Vertical axis
  • Choose the requires Output current on the Horizontal axis
  • You have to be in the white Zone. Otherwise 5U4G can not be used. (or use two in parallel)
  • Take closest curves 1...8 for the transformer AC voltage, or estimate one curve in between.
  • Note, the curves on the right chart have a smaller angle. (they are more horizontal). Meaning output voltage depends not much on actual DC current.
  • Note, this is official RCA information from the RCA tube manual 1954. You can download the 1954 and other manuals from

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, the electrical model of a tube rectifier is like an ideal 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.

Choke loaded circuit.

The best for the tube, and for low hum field radiation, is a choke loaded tube. This will force almost DC current through the diodes. This may sound unbelievable, but it works like this : The inductance of the choke is a constant current user, or constant current supply, either way, depending if the transformer is charging the circuit, of if the circuit is discharging itself into the load. When the inductance is large enough, the DC current change very little within one AC cycle. So a signal almost like DC will flow trough the choke, and for that reason through the entire circuit. This includes the rectifier diodes, and even the transformer windings. The engine storage buffer for this is the choke itself, which will generate the required voltage, to keep the DC current flowing. Like this, the whole circuit carries DC current. The function on the second capacitor is to prove an L-C filter to reduce residual hum, but AC current peaks of the capacitor are small. Much to the contrary of an C-L-C circuit, which has a very heavy pulsed charge current into the first capacitor. This current with C-L-C circuit can radiate a magnetic field, saturate the mains transformer at it's peaks, and also wear out the rectifier diodes much faster. The much more gentle L-C circuit. can load a mains transformer up to 100% of it's specified ratings, wheras C-L-C circuits can load a transformer only up to 66% (or the transformer will produce audible hum + magnetic hum field)

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. So the fact it "works" does not prove you will get long lifetime.

Please note it can not be the intention here, to explain how to design a good circuit. However we try to tell some things here, that we know are sometimes not looked at very well. Also we encourage you to read the original old data sheets. from RCA, General Electric and Sylvania, and Telefunken. You can download these and a lot more s from So look there for datasheets, and the famous RCA handbook

Some important things to remember (unsorted)

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 Anode 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 Anode 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


    Application Note AN-01

    Old Design Info- Still valid!

    Rectification with tube power supplies.

    This is probably the most misunderstood part of a tube amplifier. It can be a mistake to simply copy something, just because it was presented as "very good". Cases where good design rules were not respected we find as well with companies of high reputation, as with any other company. Interestingly, we find less of such errors with DIY. Just to mention some of the most common errors: Adding 100's of microfarad as a first capacitor for 5U4G, too low DC resistance of transformer Raa winding, or draw excessive surge current from a rectifier tube during cold start. Caused by a low cost choke, which saturates at start up, or other causes. Combine this by not measuring peak current, and start up current. Just copy schematics, makes you copy the mistakes too. Just to give the classical warning once more, when you see more than 33uF on a 5U4G, or more than 4uF on a 274B tube, such a schematic is questionable. So this can already by seen from picture files. Wheras transformer Raa Resistance can be measured simple with a low cost multi meter. Yet while peak current is hard to measure, at least you should make a simulation, for instance with "PSU Designer", which is free to use for DIY. PSU Designer will work quickly and easy, and simulate peak current with Oscilloscope-like results, at any point of the circuit you select. For the hard core users there is LTSPICE freeware from Analog Devices. Though LTSPICE will take a very long time to understand when you are new to it.

    Do not treat tube diodes like solid state diodes.

    To give you some sensitivity for this item, take very good note of the following. When comparing tubes with solid state devices, the elementary difference is: With solid state devices it becomes difficult to build such for very high voltage. High current was never a problem. With tubes, it is reversed. It is difficult to build such for high current, and high voltage was never a problem. We have to realize, when stressing exactly this natural limit, the result will cause problems. So solid state diodes have less of a problem with repeating peak current, but they definitely have a reliability problem with exceeding the peak voltage. With tubes, the situation is reversed. Tubes have little problems when the peak voltage is exceeded occasionally, but they will develop problems quickly when the peak current is exceeded. So design considerations are totally another, and it would be completely wrong to use design considerations for solid state diodes for tube diodes as well, saying "a diode is a diode". The answer to this can only be: "a data sheet is a data sheet".

    With solid state devices we all know, you can not abuse them with the peak voltage. If you do, catastrophic failure rate will rise sharply. As this is impossible to calculate with precision, good designers will measure it with in instrument, or alternatively over dimension the design ratings. This is in order to stay safely away from the damaging limits.

    Even greater care should be taken with tubes, since these are devices with limited lifetime, and they are expensive. If you abuse them with peak current at start up, or exceed it during normal operation, lifetime will be shortened severely. We repeat the same as before: As this is impossible to calculate with precision, good designers will measure it with in instrument, or alternatively over dimension the design ratings. This is in order to stay safely away from the damaging limits.

    Many good books have been written about tube power supplies, and of course we can not compress this in a few pages here. Keep three elementary things in mind, to get good tube lifetime: 1) Respect the maximum first capacitor value in the datasheet, and be aware when you use a maximum factor on the one end, you get a compromise on the other. 2) Understand and apply the derating curves, meaning at maximum current, you can not use the maximum voltage, and vice versa. 3) Use the MINIMUM copper resistance needed for a TUBE power supply transformer. Transformer building companies can not know what you need, so without specifications from your side, you get just "something". Which is only fine when you need "anything". This is so for solid state, but this is not so for tubes. You need to specify the copper resistance to them, and if they can't do the value the tube requires, you need to add the difference by using external resistors.

    Summary: These rules above, need to be respected to get good tube life, and failure free operation. For maximum lifetime of any object, and sure for electron tubes, keep some distance from maximum limits. That is: maximum capacitor value, maximum voltage, maximum current, and minimum copper resistance.

    Low residual hum. With a solid state power supply, the last final bit of hum can be eliminated by using larger capacitors. This is no problem for the diodes, as they do not suffer from transient current. With a tube power supply, the last final bit of hum, is not present because capacitors are too small, but because the choke is too small. Moreover, if circuits are not ideal you would be tempted to tweak components values, but better would be to use an improved circuit. The most commonly used circuit is Circuit #1, as below here, but this is the most unintelligent. In very many cases, simply use circuit #2 already brings an improvement. We call this "star grounding". Tough Circuit#2 is far from ideal, and Circuit #4 does the same even better and with less wiring. Circuit #3 shows one of those typical little things, you can observe when somebody does not treat a tube like a solid state diode. This makes sure the left side of the tube heater wire has the same current (and the same temperature by that) as the right side of the heater wire. Wheras Circuit #4 is such a logical and easy thing to do, but people do not understand why, and take Circuit #1, this is really painful. It is allowed to use Circuit #4, also if you do not understand why it is better, as it is free of patent rights. The words are: No ground loop risk, and electrical stray field. Circuit #5 is the ultimate circuit. Only possible with Lundahl chokes. This is the most beneficial circuit ever, for lowest hum. The choke is not only used here as an inductor, but also creates inductive decoupling of the complete rectifier parts from the amplifier circuit. There is no direct connection any more! All hum signals, no matter how they try to flow, must pass a choke now. Please also read the short explanations on the right, below here. After that I hope you understand why we say it is so silly to find Circuit #1 in most "professional" designs.

    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.
    Design Quality of Circuit1: One Star *
    Circuit 2: Added here is a bleeder resistor, a ground connection point, and if needed an external windings resistor. The ground connection point prevents any faulty ground path. This is called "star" grounding.
    Design Quality of Circuit 2: Two Stars **
    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.
    Design Quality of Circuit 3: Three Stars ***
    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.
    Design Quality of Circuit 4: Four Stars ****

    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.
    Design Quality of Circuit 5: Five Stars *****

    Bleeder Resistor: This is to empty all capacitors after power off. Using no bleeder resistor is safety issue, as voltage may stay on the capacitors for a long time. Also use of no bleeder is a reason for a sparking rectifier, as a repeated switch on, with partially charged capacitor may trigger a spark. Make sure the resistor discharges all capacitors to less than 40V in one minute. Do not mount the bleeder directly on a capacitor, because this heats the capacitor, and this is not good for reliability.

    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. So to add this 150 Ohms, you need to serialize two resistors of 75 Ohms. each at transformer winding ends. Alternatively you can add one single resistance of 75 Ohms at the center tap, which has the same effect. Then, from the tube's view you have Raa of 250 Ohms again.

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