Another HT Diode Rectifier Question.

[Leo_Gnardo]

was that 1000V rating DC or AC? Typically a 1kV DC rated plastic film cap can only stand about 350V RMS AC on a continuous basis, not 700V RMS as you might think.

Good question. By the time I see one, the Rivera snubber cap is melted into a mis shapen gumball shot through with carbon from arcing. There' are a couple Riveras I have to look at now for other problems. I'll examine their snubber caps & see if I can read anything from them. I suspect if they were really rated for 1000V AC they wouldn't fail. If 1000V DC rated - that would be marginal in this application.

The orange drop 1600V I use to replace them - that's a DC rating I'm sure.

[bob p]

why not use ceramic HV caps?

[Leo_Gnardo]

why not use ceramic HV caps?

Convenience, simply enough.

Had some 1600V OD's in the parts drawer. Probably got them from Antique/CE years ago. Also thinking if 1000V is marginal, perhaps a little overkill in voltage rating isn't such a bad thing. Rivera has some box shape film cap I'm sure is more expensive & fancy-dan than ceramic. Since Rivera's board probably has its parts loaded by machine, the box-shaped cap may be more amenable to that process. I suppose a ceramic the size of a quarter could be hand-wired on afterward but in these days when factories seem to be set up to minimize a worker's exposure to toxic substances (solder) or heat (soldering iron) it may be a matter of convenience for Rivera too.

[trobbins]

Steve - I agree with most of your comments - having worked in switchmode for many years I can see how design issues in that field permeate out in to the psyche of hi-fiers when it comes to using better diodes, but get a view that few take much effort with loop area, layout and high frequency bypass management, and rather head off with fixes such as better diodes and switchmode type larger electrolytics. But I can certainly appreciate that if a relaxed part layout with little concern for high frequency management can be 'fixed' with a simple diode swap-out, then so be it.

I'm not so settled with the interplay of leakage inductances in the PT loop and the filter capacitor loop, and how that would exacerbate the affect of diode reverse recovery to get to a level where it is seemingly so significant in many peoples minds. I'd be thinking that zero leakage inductances would make diode reverse recovery and hence diode choice a non-issue, and any designing in of larger leakage inductance would exacerbate the diode recovery issue (even though it is a common technique to smooth out the bulk portion of diode current conduction waveform).