Description

This data sheet. applies for the 5Z3 and 5U4G, which are electrically identical, only have different sockets. 5U4G uses as Octal Socket socket, of which only four pins are used, 5Z3 has an 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 types, also the EML are Slow-Start tubes, protecting the amplifier. The delay time for first function is 2 seconds, and the delay for full current is 7 seconds

We have a standard solid plate tube and a mesh version. These are electrically identical.

For ultra low ripple, it is recommended to use the Lundahl LL1673 dual coil choke, giving higher CMR than a single coil chokes. (See link to circuit diagram, at the bottom of this page).

• Slow Start ( 2...7 seconds)
• Filaments are series connected.
• 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
• 5U4G uses a black octal tube base, with four pins. From Yamamoto, the Octal 8/5p socket is recommended. This is an octal socket, but has five pin holes only. It is specially used for rectifiers.
• 5Z3 uses a ceramic tube base.

• See: CIRCUIT DIAGRAM
• See: Note 2

Some design rules for 5U4G rectifier circuits.

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 important, and yet often 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% derated 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 1...8: minimum 230 Ohms

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.

The above graph can be used in two ways.

A) 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

B) 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 derating, which means you can not use the full current of 225mA any more at this high DC voltage.

Note 2) To prevent large charge current peaks, the first capacitor (C1) should NOT be larger than 33uF. 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.

IMPORTANT: SEE RECOMMENDED CHOKE CHOKE CONNECTION SCHEMES

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