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Old 2nd August 2004, 08:12 AM   #1
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Default psu designer accuracy ?

Hi,

How accurate is Duncan Amplification PSU Designer (psud2) when using Tube Rectifiers ? I am getting different results between PSU Designer and PSpice (GZ34 is modeled as a subcircuit as well-known equation derived from Child's Equation) ?

Thanks in advance.

MB
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Old 2nd August 2004, 10:24 AM   #2
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I believe that the data for GZ34, as set up in the diode data file in PSUD2, is inaccurate. It seems to give a lower voltage drop than the 6D22S, which is a TV damper diode known for its very low voltage drop.
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Old 3rd August 2004, 06:48 PM   #3
EC8010 is offline EC8010  United Kingdom
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PSUD has tended to predict rather high output voltages for me, compared to later testing and compared to back of an envelope scribbles. Don't get me wrong, though, PSUD is very useful for checking general behavious and getting a feel for ripple currents etc. Bear in mind that it has to use a very simple model for the transformer...

All of these simulation programs are only as good as their models, and I'm heartily sick of people coming out with distortion predictions and spectra for valve circuits from PSPICE. Child's Law refers to diodes operated at saturation, but real valves are not operated that way, so its relevance is distinctly questionable.
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Old 4th August 2004, 01:45 AM   #4
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I, too, get rather lower voltages in real life than PSUD2 modeller predicts. However, I think the problem might be caused partly by my own failure to enter exact information regarding the power transformer primary and secondary winding resistances. I alos should allow for mains voltage being lower than it's supposed to be.

Another thing that's easy to overlook is the fact that the transformer primary has to feed not only the HT secondary but also any other secondaries the transformer may have, such as heater windings. This will cause additional voltage drop in the primary winding when heaters are drawing current, because of its non-zero resistance, which will then be reflected as a lower voltage in the HT winding.
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Old 18th May 2006, 09:50 AM   #5
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Wow, I guess this is a pretty old thread. That said, I have just started to play with psud2. I am beginning my first tube project and want to try to immerse myself as much as possible into all aspects of the project. Psud2 seems like a great learning tool. My question relates to the transformer variables:

The application specifies the "manufacturers data" regarding the nominal output of both rms voltage (easy) at its rated current. Am I supposed to enter the manufacturers max current for the transformer secondaries? Or am I supposed to enter the current draw presented to the power supply by my tubes?

Also, as far as the regulation percentage goes, manufacturers don't publish that data (or at least hammond doesn't). Is 5% a good baseline?

Finally, I have been testing by using a fixed current tap as "load" with the current draw of the tubes I'm working with (a simple SE ECL82 based stereo amp). Is this the best method? The program defaults to a resistive load which seems less useful to me.
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Old 18th May 2006, 10:02 AM   #6
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Enter the current actually drawn by your circuit. Yes, the default of a resistive load is less useful. 5% regulation is actually quite good. In general (time for a sweeping assumption), regulation gets worse as the transformer gets smaller. For example, a range of EI construction transformers quoted:

6VA 28%
12VA 12%
20VA 7.5%
50VA 9%
75VA 9%
100VA 8%
200VA 5%
330VA 4%

Obviously, a transformer manufacturer could make a transformer of any size to any regulation they chose (as evidenced by the 7.5% for the 20VA), but the trend is clear. I would calculate the VA rating of your Hammond transformer and pick a number from the above table. It won't be perfect, but it probably won't be far wrong.
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Old 19th May 2006, 06:38 AM   #7
eforer is offline eforer  United States
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Thanks for the help, do you find that using the method I stated above and relatively inline regulation figures that the results are reasonably accurate?
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Old 19th May 2006, 07:24 PM   #8
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by eforer
Wow, I guess this is a pretty old thread. That said, I have just started to play with psud2. I am beginning my first tube project and want to try to immerse myself as much as possible into all aspects of the project. Psud2 seems like a great learning tool. My question relates to the transformer variables:

The application specifies the "manufacturers data" regarding the nominal output of both rms voltage (easy) at its rated current. Am I supposed to enter the manufacturers max current for the transformer secondaries? Or am I supposed to enter the current draw presented to the power supply by my tubes?

Also, as far as the regulation percentage goes, manufacturers don't publish that data (or at least hammond doesn't). Is 5% a good baseline?

Finally, I have been testing by using a fixed current tap as "load" with the current draw of the tubes I'm working with (a simple SE ECL82 based stereo amp). Is this the best method? The program defaults to a resistive load which seems less useful to me.
I've generally entered the voltage at rated current, assuming that PSUD adjusts for the circuit draw. You could just measure the unloaded voltage and plug that in too. My circuits have come pretty close if I enter realistic values for all the variables (including capacitor impedence).

I like the fixed current load for most applications. It's generally a better approximation unless you actually have a resistively loaded supply - but even tube filaments don't act like a normal resistor.

Sheldon
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Old 19th May 2006, 07:36 PM   #9
eforer is offline eforer  United States
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Thanks for the replies, I feel this software has been an immensley valuble learning tool.
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Old 19th May 2006, 08:33 PM   #10
eforer is offline eforer  United States
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Another quick question. For the impedance value of the capacitors in PSUDII, should I calculate the reactance for the cap? I am using full wave rectifaction so I am assuming that the freq used when calculating the reactance should be 120hz.
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