I understand your first paragraph and what I did wrong.
I guess I've not seen a circuit based on the second paragraph but I'll see what I can scour up on the net.
Thanks, that was VERY helpful!
I guess I've not seen a circuit based on the second paragraph but I'll see what I can scour up on the net.
Thanks, that was VERY helpful!
Actually, you can use the circuit as-is with the two diodes getting 420VDC or something like that, but then you need to use a transformer with two secondaries each 360VAC instead of each 180VAC.
Jan
Jan
Weird though, when I entered the numbers correctly (I think), I get about 20V less than I measured.
Yes that is possible, PSUD2 probably incorrectly figures in the droop due to load. If you change the transformer spec from 25mA to 50mA and make sure you have the correct load, you'd get closer.
Make sure you have the same load settings, and the correct transformer wire resistance.
Jan
Last edited:
But doesn't that sort of defeat the usefulness of PSUD? Keep changing the inputs until you get the numbers that you want? The transformer is a given already as well as the caps, chokes and load. The measured result is quite a bit higher than the calculator.
Did you change the dc resistance numbers for the transformer windings? That can make a huge difference.
A simulation is only as good as the data you insert. You should measure the secondary half winding resistances, and the primary resistance, and use the equivalent resistance calculator to determine the appropriate winding resistance to use with the 180v half winding. The Tx data only provides a nominal red-red secondary resistance with a +/-20% tolerance.
Also you need to measure your primary voltage as it may not be the default value used by the Tx manufacturer.
Also you need to measure your primary voltage as it may not be the default value used by the Tx manufacturer.
Ok, I get that. My voltage is 121-123 always. Measuring the transformer if you have it in hand works but how do you plan for what transformer to buy?
In general, valve amps can cope with quite a range in mains voltage. I use the fully loaded heater voltage as the criteria for changing primary side taps, but that also requires an awareness of what your mains voltage can vary by, and what it is when you do testing. If the heater voltage ends up within +/-5% then typically no concern, although some people get quite concerned if their B+ is not within a few volts. Your PT datasheet shows a 120V tap, and you measure 122V nominal, so that's a good start to PT selection. Some people only have 110 or 115V rated PT's, and measure well in excess of 120V, so it is more of a concern and that may be better managed with a bucking transformer.
The other issue I mentioned seems more problematic. How can you put in the correct DCR if you don't have the actual transformer in hand and the published data isn't going to give you accurate results?
The only accurate result is a measurement. The sim should be close, as the PT data does provide red-red resistance and i think pri resistance. But perhaps the issue is why do you need an accurate value?
@WntrMute2 Tony said it all. You are right that the point of the sim is to get a good idea of what to expect before you commit your wallet. But PSUD2 is only as good as the data it is fed, and often you don't have the required xformer data, and/or not accurately. Even the ESR of the decoupling capacitors can make a difference. I would say, if the sim is within 10% of the real measurement, you've done well.
Jan
Jan
Mostly, I'm trying to learn how to use the tool. If I want a particular B+ it would be nice to have the data I need to order the correct parts.
It's a good tool for that, but as Tony mentioned, the final proof is the measurement.
And it's also helpful to know your error budget.
For instance, if you design an amp for B+ of 380V, would it be bad if it turned out to be 400V? Or would it be better to have it at 360V?
That can be useful if you try to figure out the max and min mains voltages it has to work with.
Jan
And it's also helpful to know your error budget.
For instance, if you design an amp for B+ of 380V, would it be bad if it turned out to be 400V? Or would it be better to have it at 360V?
That can be useful if you try to figure out the max and min mains voltages it has to work with.
Jan
So I think I have the wrong power transformer. The primary is NOT center tapped and measuring unloaded I have 494 volts end to end. When I enter the values for the transformer should it be 494 or half that. 494 and at cap2 the voltage is too high 609 and at 247 I end up with 285 volts B+ with a bridge.
Thanks for any help you can provide
Thanks for any help you can provide
Perhaps best to identify the make/model of transformer, or clearly describe the transformer, as your comment about the 'primary' not being center tapped sounds ambiguous.
Also it's good to read the help file first, such as may be located (depending on your installation, at file:///C:/Program%20Files%20(x86)/PSU%20Designer%20II/help/html/edit_transformer_properties.html
Also it's good to read the help file first, such as may be located (depending on your installation, at file:///C:/Program%20Files%20(x86)/PSU%20Designer%20II/help/html/edit_transformer_properties.html