• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is PSU Designer II correct?


2003-08-20 4:03 pm
When I found PSU simulator from Duncan's, I shouted with joy!

But I see some weird things happen now. See the picture attached please.

I set 100ma for output tube stage, and 6ma for driver tube from 330V (RMS) transformer. I added 4k5 in order to drop voltage for driver stage. Oh, I am talking about a pentode SE amp.

Well, according to my manual calculation, voltage in c2 should be around 250V, because 27V drops from the previous one by 6maX4.5k)

But the result says 190V. Wow, I cannot understand this result. Moreover, when I measured a REAL amp with my tester, I found that my calculation was right and PSU II was wrong.

I tried to contact Duncan for this matter, no reply has been made. Anybody can explain this? What did I miss?


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I doubt that it's the simulator - it's probably that your model doesn't match reality.

Is the no-load voltage and resistance for the transformer correct? It has to include not just the secondary R but the reflected primary R as well.

Is the ESR of the caps and inductors the same as your actual parts?

Beware using current sources in simulations - they are not real. For example, what's the voltage that appears across an unconnected current source? Inifinite. You're safer using a resistor with the equivalent load.

So if you already have the circuit built and measured, why are you worried about the simulation?