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EE40 Universal Power Supply board for rectifier tube, or silicon diodes.

Kit Number: 311-040-39

Description

This simple but effective PCB allows you to find out the ideal circuit, without getting a mess. There are many (very many...!) cases when hum ist generated by unlucky, or wrong wiring. Then, capacitors are made larger and larger, solving the problem not really, and cause other problems such as tube wear out, rectifier sparking and capacitor charge peaks radiating into the pre amplifier. Also we encourage you to use a Lundahl dual coil choke, for which the PCB is prepared. Though this is no requirement, and common single coil chokes can be used as well.

Most parts are supplied with the board.

There are three ways to use EE40

1) As evaluation board on the bench. In this case, the tube socket is mounted together with all other parts at the components side. The PCB socket is supplied.

2) As final board in an amplifier, connecting the tube socket with wires to the PCB, and mildly drill the heater wires. In this case, use the wiring numbers as printed on the PCB. This requires your own socket with solder lugs (not supplied)

3) As final board in an amplifier, with the tube socket mounted on the PCB. In this case, the tube socket will be mounted on the BACK of the board, at the solder side. This is a little bit of a trick with the tube pin connections, but it is possible as follows, and it works well. The positioning slot of the socket has to be mounted, with one pin rotated. For this, look at the BACK of the board, there is a clear white dot, near the socket pins. This dot, you have to align with the center slot of the tube socket. (This dot is only printed at version 1.0 or higher). The PCB socket is supplied.

Features:

• Rectification: You can Use silicon diodes, or use tubes. Tubes such as: 5U4G, 274B, 5Y3, GZ32, GZ34, 5AS4, 5AW4, 5AX4, 5AZ4, 5R4, 5T4, 5V3, 5V4, 5W4, 5Y3, 5Z4, AZ31, AZ32.
• Tube HEATER: Option to add a small series resistor to adapt heater voltage. Like when using smaller tubes such as 274B or 5Y3, on a higher current 5V winding, voltage may rise above 5V otherwise. There is a solder bridge to short this resistor, if not used. Across the heater itself are measurement pads on the PCB for quick testing. For large tubes like 5U4G of larger rectifiers even, count with appr 0.1V voltage drop internally, across the socket pins. So for 5V tubes, 5.1V on the test pads would be just right.
• Lundahl dual coil: In case you use these: PCB numbering on EE40 = Same as Lundahl numbering.
• Not a Lundahl coil. If a standard coil with one winding is used, apply a wire bridge from 6 to 4, and connect the coil between 3 and 1. You will note, the choke is now in the ground line. Electrical function is the same, but now electrical fields between choke and ground are lower, and the choke will become mechanically more silent.
• Test Pads to measure DC Output Current. A resistor R7, of 1 Ohms can be put in series. With a VOLTMETER, current can be measured. 100mV equals 100mA. Such a simple provision, but you will like it very much. This resistor is in the ground path, at a place where it has no high voltage on it. Also it is not on the impedance path of the output capacitors. If you don't want to use this option, solder a wire piece in the place of R7.
• Capacitors. For Electrolytics, maximum voltages stop around 500V. When experimenting perhaps with the circuit unloaded, it would raise the output voltage a lot. So we have put two 350V capacitors in series, meaning maximum unloaded voltage can be 700V.
• Load resistors R2 and R3. , Provide the discharge at power off, and prevent tube sparking. These are 1 Watt types, in which we dissipate 0.8 Watt with an unloaded EE40 board. Resulting in appr 0.6Watt if the output is loaded. The value of one resistor = 0.5 * (specified transformer voltage)^2. Example: With a 450V AC transformer, we get R2=R3=0.5*450*450=100k. If voltage doubling is used, you have to calculate with 2x the transformer AC voltage.
• The balancing resistors R5 and R7. These are only for balancing the output capacitors. These are 470k, 1/4 Watt. Even when not using capacitors C1 and C2 (like when using an L-C filter) R2 and R3 should be applied, in order to achieve a minimum load, and also to discharge the output capacitors faster (via the choke).
• Radio Fuses. The mains fuse, F1 works against shorts and mistakes. The fuse F2 is for output overload, and depends on the output current.
• Power supply boards are red color, amplifier boards are blue color.
• Blue Hazard LED. Prevents painful mistakes :)
• MAINS Part. All mains circuitry MAY be done via the board. So the board has a mains voltage sections as well. Using this is not required, you can also wire the mains transformer primary your own way. Using the EE40 board for this, would give more wires to the board, but overall this reduces the total wiring, because many connections are made now via the PCB.
  • In case you use the mains part of the EE40 board:
  • 1) Transformer has one single primary winding of 115V or 230V. This is connected to Y1 and W2 of the according 115V or 230V pad.
  • 2) Transformer has 2x 115V primary. Connect those two windings to the 115V pad or to the 230V pad, to choose the primary voltage. W1-Y1 is one winding, W2-Y2 is the other winding. Mind the polarity of the windings, W1 and W2 have the same polarity.

How to use the board

there are six ways to connect the transformer high voltage secondary, described below here. Please be aware, some transformer have two secondary windings, but to use these a a center tapped transformer, is only possible if the manufacturer allows this use. Any unspecified use may result in mechanical noise. These methods (1...6) are automatically selected by adding the parts on the PCB.

Rectification methods.
Method	Diode type	Transformer must have center tap?	Voltage doubling	Insert Silicon diodes:	Example for 250V AC. (DC voltage depends on load)
1	Silicon only	Yes	No	D1, D2	250-0-250 primary will give appr 300V DC. R2=R3=31k. Take closest commercial resistor value.
2	Silicon only	No	No	D1, D2, D3, D4	250V primary will give appr 300V DC. R2=R3=31k. Take closest commercial resistor value.
3	Silicon only	Yes, but this wire is NOT connected to the board.	Yes	D1, D2, D3, D4	250-0-250 primary will give appr. 600V DC. R2=R3=125k. Take closest commercial resistor value.
4	TUBE only	Yes	No	none	250-0-250 primary will give appr 300V DC. R2=R3=31k. Take closest commercial resistor value.
5	HYBRID Click here for notes	No	No	D1, D2	250V primary will give appr 300V DC. R2=R3=31k. Take closest commercial resistor value.
6	HYBRID Click here for notes	The transformer must have it, but we do NOT connect it.	Yes	D1, D2	250-0-250 primary will give appr. 600V DC. R2=R3=125k. Take closest commercial resistor value.
Info	Why Hybrid? This creates an artificial center tap with two diodes. This allowing tube rectification with a single winding only. See Note

 

Capacitor / Choke configurations
	Type	Choke Type	Wiring of connections 1-3 and 4-6	Note
1	C-L-C	Single Coil	Choke at 1-3, Wire Bridge from 4-6	This will keep coil at ground level for more safety.
2	C-L-C	Dual Coil	Lundahl choke, pin numbers equal 1-3 and 4-6. If not Lundahl: 1 and 6 have same polarity	Lowest noise
3	C-R-C		Resistor from 1-3 and from 6-4. External Resistor, with cooling.	Has residual AC. Possible for Push Pull with feedback.
4	L-C	Dual Coil	Lundahl choke, pin numbers equal 1-3 and 4-6. If not Lundahl: 1 and 6 have same polarity Leave away: C1, C2, but still use R2, R3	Ultimate way, but requires 2...3x larger inductance. Allows highest DC power to be pulled from the rectifier.
5	L-C	Single Coil	Wire Bridge from 6-4. Choke at 1-3. Leave away: C1, C2, but still use R2, R3	Ultimate way, but requires 2...3x larger inductance. Allows highest DC power to be pulled from the rectifier.

 

What is included:

• PCB EE40
• Capacitor C3 an C4, BHC Aerovox 390uF 350V
• Octal Tube socket, 4x Diodes 1N4007, 2x Fuse holders
• Resistors R4, R5, R6, R7, blue LED

Not included:

• Choke and mains transformer
• Banana connectors. We recommend such: Click here
• Rectifier tube. R1, R2, R3, C1, C2 and the fuses F1, F2. These parts all depend on the transformer, tube of your choice, and use of the circuit.

Please note this: These capacitors are superb quality NOS Audio Capacitors from 1995, made in England, but they should be formatted before first use. Formatting is nothing but a very slow start, at very FIRST USE. The EE40 board itself can be used for this as follows: When building it, do not solder the capacitors on it yet and do not connect the choke. Now the connections 6 and 3 supply an unstabilized voltage. Connect 6 to the plus of one capacitor via a 1 Meg resistor, and 3 to minus, and hook up a DC voltmeter to the capacitor as well. Switch on the EE40, and this will slowly charge the capacitor. Monitor it, and stop at 350V, or as far as the EE40 goes. Then switch the EE40 board off, and wait for the capacitor to be discharged, before removing it. Then repeat with the other capacitor. Even so, you can repeat the formatting just by switching on and off the EE40, and you will see, the second time it charges much faster. When the capacitor charges in 7...10 minutes to 2/3 of the final voltage, the formatting was successful. Though not strictly needed, formatting is the best for never used before capacitors. After that, capacitance is closer to the rated value, and less leakage, and lifetime will be longer.

Capacitors C1 and C2, depend on tube used, or perhaps even an L-C filter is used, and C1 and C2 are not needed. So C1 and C2, are your own choice.

 

EE40 Board Order Number: 311-040-39

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Notes, and tech talk.

Why is the Transformer Output fuse in the Ground Line? Most of the time, the fuse is directly placed at the output, but no normal radio fuse can fuse 700 DC (which is the unloaded voltage) safely. At such high voltage, at a bad short, there is a risk the fuse may explode. Sand filled fuses are safer, but I wouldn't bet on what happens if you fuse 700VDC with a 230V AC fuse. The fuse is now in the return path of the AC current.

The Artificial center tap. Please read also the "fuse" part. above here. To use a tube rectifier, requires normally a center tapped HV winding. If this is missing on the transformer, we can still use this transformer, when we create an artificial center tap, with two silicon diodes. Before explaining this, first look at a classic center tapped circuit: The center tap is GROUNDED. This is very important to keep in mind. To understand how the VIRTUAL center tap works, look at the negative of C2 in this schematic This is ground level. We have the choke in between, but it filters out only residual AC before the choke. The virtual center tap would work just as well without the choke. With a single coil choke from 4-6 and a wire link from 1-3, C2 is even hard-grounded. And yes, feel free to try this with the EE40. So regard the negative of C2 as GROUND level, just for better understanding. The fuse F1 plays no role for the functioning of the circuit. To the fuse is D3 and D4 connected, and the transformer has no center tap. Due to the AC signal, ALWAYS either D3 or D4 is in conducting state, and in conducting state, there is only 0.7V across it. This means at the positive half of the mains, D3 is conducting and the fuse is clamped to ground by the conducting diode. At the other half of the mains, D4 is conducting. So all of the time, the fuse is clamped to ground. The only difference with a real center tap is this 0.7V of the conducting silicon diode, but in compare the voltage drop across the tube rectifier (some 20...35V) this can be neglected. It would effectively only change the curve of the tube diode, by adding 0.7V DC to it. Voltage of the tube diode, and also it's resistance are so much higher than the silicon diode, there is almost no change at all. Virtues of tube rectification (higher dynamic resistance, less aggressive charge spikes, slow start and peak current limiting) it stays all unchanged. Also on the tube curve itself, lifting it with 0.7V is hard to see. This way, indeed still normal tube characteristics will determine the behavior.

Voltage doubling. Another thing we can do with the artificial center tap, is voltage doubling. A 250V-0-250V winding with tube rectification would normally give 300V DC (depending on the load of course). WIth an artificial center tap, voltage doubling occurs, and we get 600V DC. Note: In case of voltage doubling, do NOT connect the center tap together with the diodes D3 +D4. So the center tap must not be connected to the PCB, but D3+D4 must be soldered in, and then you have voltage doubling. Also with a tube rectifier. Correct connections for this, are in the table..

What is a center tapped winding? Under cost pressure, transformer winding companies over simplify this, unless you give clear orders how to do it. Here is why. Because of AC, and because we use rectifiers, a center tapped winding carries only current through one section of course. This would be fine with a toroid, or with any other core, when BOTH halves of the tapped winding are wound TOGETHER, so physically at the same place, and in addition have the same geometry too. This can only be done with bifilar winding, or a split chamber. Bifilar is not possible with High Voltage. A split chamber, you can check if it there, from the outside. Is this not visible, then you don't have it. The cheaper way, the usual way, to lay one package over the other, will lead to uneven wire length, and uneven load, due to copper resistance difference, and uneven magnetic coupling. Effectively this will give some l DC magnetization of the core. Then, at large voltage, this would saturate the core, which gives a specific noise, which you may have heard before. It sounds like "hummmm". Particularly under dimensioned transformers will have no air gap, because air gapped cores cost more, and are larger dimension, even requiring a longer copper wire. Meaning however, under dimensioned transformer can withstand absolutely no DC component. To be on the safe side, such windings should be dimensioned a factor 1,7 larger, is what Per Lundahl told me. Will EL CHEAPO company do this? No, I don't think so. Simply inquire if their center tapped winding balanced (symmetrical) and if the transformer has an air gap. When they dispute the need, or don't understand why you say this, you can already expect what you are getting. Alternatively, for low cost transformers, you should think of the HYBRID connection. This avoids the problems resulting from a not correct constructed tapped winding.

Raa Winding resistance. Rectifier tubes require always a minimum Raa windings resistance. This special knowledge of tube transformer making has gone with the wind of modern times. But for the tubes itself, this requirement has not gone at all. Each rectifier requires a certain MINIMUM windings resistance, or the tube will have low lifetime, or even show a white spark at switching on. In classic circuits, transformer Raa is measured at the tube socket, between the tube Anodes, when the amplifier is off, mains cable and rectifier tube unplugged, and capacitors discharged. In many cases this value is much too low. This major design error can be fixed by adding an external resistor in each side of the Raa winding. 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 at each transformer winding ends. Alternatively you can add one single resistance of 75 Ohms at the Cathode Tap, which has the same effect. Then, from the tube's view you have Raa of 250 Ohms again. So to be sure, unplug the mains, wait for capacitors to be empty, unplug the rectifier tube, and measure transformer Raa at Pin 4 and 6 of the Octal socket. This value is important, it may not be too low, or tube problems can occur, and transformer hum will be too loud also. This simple measurement is HIGHLY interesting to do on expensive tube equipment. Any yes, chances on a mistake is higher than finding no mistake. It is sad but true, and it caused so many rectifier to die too soon. But really, we can not have transformer builders chance the requirements of tube data sheets?! That would be silly.

The reason why dual coil chokes are made. Look at the schematic, and you will see how a dual choke cuts the ground path. That is the whole reason for it. The below schematics explain the effect, but is stays difficult to understand immediately Here is the usual schematic1 and schematic2, which also applies for any single coil choke. Schematic #3 applies for a dual coil choke. The AC ground path is cut, because for 50Hz, the choke is very high resistance.