rectifier voltage drop

[dsavitsk]

Using a GZ34, I am measuring 640VAC in the input side (320 plate to center tap) and 290VDC right after the rectifier and before the first filter cap. I know the data sheet says 17V dropped per plate, but I assumed that this meant (320 * 1.414) - 17, but am I wrong? If I want at least 370VDC before the first filter cap, do I need a 400-0-400 transformer? Duncan amps tool gives me totally different results.

[jeff mai]

Are you sure the first cap is in circuit? The voltage you're getting is about right for a choke input filter.

[dsavitsk]

I'm actually cheating and using this PS http://welbornelabs.com/ps10.htm with a tube rectifier, and the readings are from before the first cap.

[jeff mai]

Have you checked the output voltage with a load?

From the example shown on Welbourne's site, I'd figure you to get much more than 290V output.

[jarthel]

Originally posted by dsavitsk
I'm actually cheating and using this PS http://welbornelabs.com/ps10.htm with a tube rectifier, and the readings are from before the first cap.

any chance of telling us what diode is used? can you also include the resistance and capacitance for the snubber? thank you.

[blacklight]

Ach, forget it. I misread your post. Sorry.

[dsavitsk]

A few more experiments: I used the same tube and transformer with a basic pi filter and a 69K load. I measured 420VDC on the output which means that the tube and transformer seem to be operating normally.

So, can anybody help with why the huge V drop across the tube in the other instance? Any suggestions as to what to look at? I don't seem to be generating any undo heat anywhere and no fuses are tripping, so i am just totally stumped. Any ideas at all?

[jarthel]

have you ask welbourne?

[dsavitsk]

Originally posted by jarthel
any chance of telling us what diode is used? can you also include the resistance and capacitance for the snubber? thank you.

The diodes are just standard high voltage diodes. But, I think the choice of what cap and resistor to use is proprietary. However, if you search this site, you will find rules of thumb for choosing both -- I'm not trying to be cryptic, I just don't remember them off hand. I will say, too, that the diodes seem to be making a lot of noise (as in a buzzing) when I used them.

Originally posted by jarthel
have you ask welbourne?

I am waiting for a response, but I thought someone here might know something.