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B+ voltage drop

Is the 460VDC loaded or unloaded? If that's with no power tubes drawing current, it will be much higher than under load.
 
I'd confirm that transformer impedance number. If that is higher than actual it will show a lot of voltage drop. There is a calculator function where it asks for primary and secondary voltages along with DC resistance on primary and secondary to calculate it.
 
gadget73 said:
I'd confirm that transformer impedance number. If that is higher than actual it will show a lot of voltage drop. There is a calculator function where it asks for primary and secondary voltages along with DC resistance on primary and secondary to calculate it.
Click to expand...

Can you elaborate on this please... Is this a function of PSUD ?
 
Did you use the transformer unloaded voltage for the data in PSUD? It requires the offload voltage along with winding resistances. When you edit the transformer data, the calculator is available as a subfunction on the data window.
John
 
If I edit the transformer properties I have these options.

upload_2021-2-26_13-32-51.png

Do I need to setup both or just the source ?

I've set the Nominal Output and left the regulation at 5%

upload_2021-2-26_13-31-45.png

Set the source impedence data

upload_2021-2-26_13-32-9.png

I still only get 420Vdc in the simulation though
 
Good point. I measured that at 390 which brings the simulation to 433Vdc. Still 40v shy of the readings I got.
 
I looked up the Edcor transformer you mention earlier. It is rated 380v when loaded with 200mA. Do you really only get 390v when it has nothing connected to the secondary? I would suspect it to jump up a fair bit higher.
 
You need to measure offload voltage with nothing connected to the secondary. Pull the tubes including the rectifier and measure the AC secondary voltage from one side to the CT. That is the number that PSUD2 wants for offload V.
 
Oh, OK.... I didn't realise that and would explain why my voltage readings are low.

I'll have a play later and see what I get.

Thanks
 
Hyakuya said:
....I saw 460Vdc on my build.
Click to expand...

When I model what you showed earlier but use the correct values from Edcor for the PT (380V @ 200mA) and use 8% regulation, which then gives 410V unloaded (as I think you previously said). PSUD predicts very close 457V compared to the 460V you measured.

upload_2021-2-26_9-11-57.png
 
@Hyakuya

What B+ voltage is it you actually want? Is it that you truly want 535V B+ as mentioned earlier, or that you expected to see 535V but don't, so you're wondering what's the problem?

If you want more than ~460 you're going to need a different transformer having a higher secondary voltage. If you truly want 535V B+ you're going to need more like a 420, 430V transformer rather than 380V.

Bear in mind transformer secondary voltage is given at the rated output current, not unloaded.
 
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I think @StepheK just built this amp using the same (?) Edcor PT. Perhaps she can tell you what voltages are present in her PS.

You should also keep in mind that the voltage rating of your first cap should be high enough to safely withstand the peak it will see when power is first applied, not just the voltage it sees after the PS has stabilized.
 
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