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.
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.
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.
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.
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.
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.
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.
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.
eforer said:
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
Mr Grumpy says there's no such word as "amperage" - it's "current".
If you look in the menu for the load current, you'll find that there's an option for a stepped current load. Set one current at your quiescent current, and the other at your full load current. Do a search on this forum for use of the stepped current function in PSUD2 - it is an extremely valuable tool.
If you look in the menu for the load current, you'll find that there's an option for a stepped current load. Set one current at your quiescent current, and the other at your full load current. Do a search on this forum for use of the stepped current function in PSUD2 - it is an extremely valuable tool.
Re: Mr Grumpy says there's no such word as "amperage" - it's "current".
http://www.m-w.com/dictionary/amperage
http://www.m-w.com/dictionary/amperage
"Orientate" is another misceganation from that family of glorious words invented by management to justify meetings that produce nothing but memos. Personally, I'd like to diversificate my forward-looking thinking strategies to incorporate all emergent languagification and communication possibilities.
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