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Adding up all the currents! I'm lost!

 

Hi all,
I am attempting to understand this PSU2 app. I want to design a power supply for a tube amp that has a B+ of around 350Vdc, and B+1 at about 330Vdc, and my final B+2 (preamp supply) at about 180Vdc. But I have yet to get it to match on my bench test bed. I think the main issues is the load! and the current being drawn.
I have a PT that can supply about 100mA at 325-0-325. Meaning 650V, then after the rectifier I have about 477Vdc.Which is way too high for my 6V6 tubes!. I then use 3 zener diode of 33V drop to bring down the voltage to about 380Vdc. at my first C1 cap. (meaning that is B+). However, depending on the load I put on the PS, changes this of course, and I am reading in the range of about 300Vdc. Right now as a test, I put a 5K resistor at the end of the line.
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My question for you all. is in regrades to current draw. On the PSU designer it shows in the chart, the calculated RMS voltage and current. To get my total current being pulled from the transformer do I add up all these currents? If so, then I have way exceeded the max current on this transformer!
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Additionally, I am totally guessing on how to load down this PS. I stuck that 5K on the end. Its drawing about 30mA at C3. But is that too much? or too little? I know a typical 6V6 push pull amp would put out about 15W at about 125mA. But I am designing this to run at a much lower wattage. Something more like 10W or even 8W if possible.
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See my simulation below. the voltage at C1, C2, C3. would be acceptable, if the currents were correct and my load correct. But with these component values on my real test bed, I am a bit off. Please note, that since the PSU app does not allow you to add in series diodes, I had to fudge the T1 voltage to compensate for a 99V drop, so you will see it listed at 285V, not the 325V it is speced for.
Please help. Do I have the correct values for R1 and R2, R3?
Thanks.
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Hi,?
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A couple of suggestions that might be of some help:
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In PSUD:
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  • When you start up, there will be some large peak currents. You might want to use "after a reporting delay" and pick 1 second to work with the values you have. This will let some of the high peak currents settle down and reduce the RMS to give you some steady state figures
  • When adding loads, you need to load the left hand side sections rather than just the right. Insert a current tap just before R1 and load it with 80mA for starters, this might be a good value for a pair of 6V6s. Insert a second current tap before R2, I'm guessing this is for 6V6 screens use 4mA as a starting figure
  • Finally, change the 5K at the end for a current load. Try 10mA if it's just for some preamp stuff, more if you have a tuner etc.
  • The transformer voltages don't look out of place but the resistance looks low for powering a pair of small output tubes. How did you measure/calculate this??
For your PSU build in practice:
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  • Try and think of ways to avoid the Zeners; while they will drop voltage they will greatly amplify any voltage regulation problems so will be far from ideal
  • Your 325-0-325 as you've guessed is probably going to be over the top. Try and source another (hamfests etc.) or swap with someone for a lower voltage, 250-0-250 or 275-0-275
  • If you can't source/swap/beg/borrow there are companies like Hammond etc. that make a wide range of new transformers
  • Check out schematics of other amplifiers / PSUs that have been made before - it's always a good source of inspiration and a reference point to calibrate your ideas
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General:
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  • Data on the 6V6 can be found here: , the linked data sheets will give typical voltage and current draw information for a variety of different amplifier classes
  • Data on the 5Y3 can be found here: , the linked data sheets show a variety of transformer input voltages and expected DC outputs which you can use to calibrate your work on PSUD
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Hope this helps, please message back and let us know how you get on or if you get stuck with any of the above.
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Regards,
Duncan
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Excellent suggestions! thanks!
I did not know that about the zeners. I have used them before on other projects, and felt like they worked okay. Other amp builders turned me on to the zener trick.
I looked up the specs on the tubes, and this is where I am coming up with my voltages and currents.
As for the DC resistance on the transformer. you are correct, that number is wrong! I thought I had fixed that on PSUD! the data sheet on the PT shows it to be more like 277 ohms. I'll fix that.
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I will give this all a try and get back to you with my results!
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DS
 

As for the DC resistance on the transformer. you are correct, that number is wrong! I thought I had fixed that on PSUD! the data sheet on the PT shows it to be more like 277 ohms. I'll fix that.
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Sounds good, please use the ohms from one leg only, not across the whole HV winding (it's to do with the way PSUD2 works). Also please factor into account the resistance of the primary to give an overall impedance, there's some details in the following text to help with this.
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If it's possible to measure the resistance of one leg and the primary, and also measure the off-load voltage you can get a good approximation of what the source impedance should be with the Source Impedance Calculator built into PSUD2.
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Right click on the transformer and select edit:
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This will give you the Edit transformer properties dialog:
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Click the [...] button shown and you will get the Source Impedance Calculator:
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From here, you can enter the mains supply voltage and primary winding resistance, also the secondary voltage and resistance (one leg only). It will then figure out an estimate of the source impedance for you. Please be aware the off load voltage will be higher than the rated secondary voltage of the transformer; that's what it will provide when it's loaded down.
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Regards,
Duncan
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thanks for the additional information.
I found the datasheet for the transformer, and collected the DCR values and needed voltages.
I adjusted the PSUD2 app values as you suggested, and I removed the zener (compensation) from the formula. Full PT voltage is 325V.
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Still does not make much sense to me! The numbers just do not add up the way I would expect them to. My VC1 should be a lot higher than 306Vdc.
For grins and giggles I pulled a schematic from a popular fender 5E3 design site, along with data 9and design tips) from The Valve Wizard, and input these values into PSUD2. Even with this new information, the program did not generate the numbers even close to the actual values that were on this sample schematic I pulled!
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Is VT1 RMS voltage of 287.6 the rectified voltage?? that just seems real low. I think I was measuring way over 350V on my bench test bed.
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So at this point, I think I will just leave it as it is, and finish building the rest of the amp circuit, and then hook up this supply and carefully bring up the mains and measure what I get. Adjust as needed to bring it into spec. I think this Hammond PT, is only around 70mA. I think I would need closer to 125mA, but you would think you could control the amount of current being drawn, by lower plate voltage and biasing the amp cooler! But perhaps I don't understand it. I'm a solid state engineer.... tubes were before my time!
What I do not yet understand about tube amps is how the current changes as you increase signal, and how the OT impedance affects the current load. So I am concerned that this little PT will be way under spec, causing it to get real hot, or even blowing it out. But I will try it anyway, since it cost me zero $. If needed, I will buy a new appropriate speced PT.
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Side note for PSU2 design revision suggestions... It would be convenient to show the wattage at each of the nodes. the other suggestion is on the colors of the graph lines. They change each time you run the simulation! It would be nice to make these static with color choices of your own. And I would eliminate YELLOW all together. Its too hard to see!
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Thanks.
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Yup, tube amps really are different from their younger cousins!

EL34world.com is a great place to learn about this stuff.? Well informed folks over there.? Also, is reputable.?

chris

On Fri, Jan 3, 2025 at 12:18?PM orders2010 via <orders2010=[email protected]> wrote:
thanks for the additional information.
I found the datasheet for the transformer, and collected the DCR values and needed voltages.
I adjusted the PSUD2 app values as you suggested, and I removed the zener (compensation) from the formula. Full PT voltage is 325V.
?
Still does not make much sense to me! The numbers just do not add up the way I would expect them to. My VC1 should be a lot higher than 306Vdc.
For grins and giggles I pulled a schematic from a popular fender 5E3 design site, along with data 9and design tips) from The Valve Wizard, and input these values into PSUD2. Even with this new information, the program did not generate the numbers even close to the actual values that were on this sample schematic I pulled!
?
Is VT1 RMS voltage of 287.6 the rectified voltage?? that just seems real low. I think I was measuring way over 350V on my bench test bed.
?
So at this point, I think I will just leave it as it is, and finish building the rest of the amp circuit, and then hook up this supply and carefully bring up the mains and measure what I get. Adjust as needed to bring it into spec. I think this Hammond PT, is only around 70mA. I think I would need closer to 125mA, but you would think you could control the amount of current being drawn, by lower plate voltage and biasing the amp cooler! But perhaps I don't understand it. I'm a solid state engineer.... tubes were before my time!
What I do not yet understand about tube amps is how the current changes as you increase signal, and how the OT impedance affects the current load. So I am concerned that this little PT will be way under spec, causing it to get real hot, or even blowing it out. But I will try it anyway, since it cost me zero $. If needed, I will buy a new appropriate speced PT.
?
Side note for PSU2 design revision suggestions... It would be convenient to show the wattage at each of the nodes. the other suggestion is on the colors of the graph lines. They change each time you run the simulation! It would be nice to make these static with color choices of your own. And I would eliminate YELLOW all together. Its too hard to see!
?
Thanks.
?
 

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- Ian


On 1/4/2025 07:36, Chris via groups.io wrote:

Yup, tube amps really are different from their younger cousins!

EL34world.com is a great place to learn about this stuff.? Well informed folks over there.? Also, is reputable.?

chris

On Fri, Jan 3, 2025 at 12:18?PM orders2010 via <orders2010=[email protected]> wrote:
thanks for the additional information.
I found the datasheet for the transformer, and collected the DCR values and needed voltages.
I adjusted the PSUD2 app values as you suggested, and I removed the zener (compensation) from the formula. Full PT voltage is 325V.
?
Still does not make much sense to me! The numbers just do not add up the way I would expect them to. My VC1 should be a lot higher than 306Vdc.
For grins and giggles I pulled a schematic from a popular fender 5E3 design site, along with data 9and design tips) from The Valve Wizard, and input these values into PSUD2. Even with this new information, the program did not generate the numbers even close to the actual values that were on this sample schematic I pulled!
?
Is VT1 RMS voltage of 287.6 the rectified voltage?? that just seems real low. I think I was measuring way over 350V on my bench test bed.
?
So at this point, I think I will just leave it as it is, and finish building the rest of the amp circuit, and then hook up this supply and carefully bring up the mains and measure what I get. Adjust as needed to bring it into spec. I think this Hammond PT, is only around 70mA. I think I would need closer to 125mA, but you would think you could control the amount of current being drawn, by lower plate voltage and biasing the amp cooler! But perhaps I don't understand it. I'm a solid state engineer.... tubes were before my time!
What I do not yet understand about tube amps is how the current changes as you increase signal, and how the OT impedance affects the current load. So I am concerned that this little PT will be way under spec, causing it to get real hot, or even blowing it out. But I will try it anyway, since it cost me zero $. If needed, I will buy a new appropriate speced PT.
?
Side note for PSU2 design revision suggestions... It would be convenient to show the wattage at each of the nodes. the other suggestion is on the colors of the graph lines. They change each time you run the simulation! It would be nice to make these static with color choices of your own. And I would eliminate YELLOW all together. Its too hard to see!
?
Thanks.
?
 

On Fri, Jan 3, 2025 at 06:18 PM, <orders2010@...> wrote:
> the other suggestion is on the colors of the graph lines. They change each time you run the simulation!

>It would be nice to make these static with color choices of your own. And I would eliminate YELLOW all together. >Its too hard to see!
?

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## Yes, get rid of the yellow.? ?I have to keep clicking on one parameter...and it changes through every colour available...till I get the colour I want.? It's no fun when say? Voltage and current are the same colour.?
 

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I shouldn't think it too onerous to have a class table where voltages are one style, currents another. Resistor colors sans white could be used: v1 black, v2 red, v3 orange...
- Ian

Jan 4, 2025 15:30:38 Jim VE7RF via groups.io <jim.thom@...>:

On Fri, Jan 3, 2025 at 06:18 PM, <orders2010@...> wrote:
> the other suggestion is on the colors of the graph lines. They change each time you run the simulation!

>It would be nice to make these static with color choices of your own. And I would eliminate YELLOW all together. >Its too hard to see!
?

?
## Yes, get rid of the yellow.? ?I have to keep clicking on one parameter...and it changes through every colour available...till I get the colour I want.? It's no fun when say? Voltage and current are the same colour.?

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