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In Reply to: RE: How do I double the voltage on diodes? Parallel or series? posted by Cleet Torres on August 21, 2014 at 05:12:06
Series, but put a 0.001uF disc ceremic Cap across each of them to keep fast transients from exceeding their PIV ratings due to tolerance and strays.
Rick
Follow Ups:
Mmm, any particular manufacturer # you would recommend?
After giving it some thought I'm going to use three diodes per leg to accomodate voltage surges, so it looks the $$ I'm saving using what I got is going out on caps to allow me to use what I got. One cap per diode right?
Thanks
Cleet
"One cap per diode right?"
Right. The notion is to keep the voltage sane while the diodes have a chance to clear out their stored charge or start conducting. Actually it wouldn't hurt to parallel them with some large resistors also, something that runs about 10X their reverse leakage current.
Best, Rick
Prolly best to get 1kV rated caps.
Good luck!
and probably cheaper to just get some 1.2Kv Schottkys and plug them in. I don't have suitable ceramic caps lying around, so I'd be putting in an order to mouser anyways.
Nevertheless, thanks for the info gents. Knowledge is always a good thing.
Regards
cleet.
I agree with Tom. For many years using a diode rated 2.5 times the PIV voltage reduces failures to about zero. This formula was originally found in Ham Radio Amateur Radio Handbooks regarding power supply design.
2 times the operating voltage for a bridge rectifier is the minimum value I would recommend too.
So minimum 3 MUR860's in series per leg, preferably 4? Alternatively two 1Kv rated schottskys? Either way I need some bypass caps.
High voltage schottkys (2Kv plus) are prohibitively expensive.
Why not use 2x low noise UF4007 diodes per leg? I hear no performance difference in-between other 'high-end' diodes and the UF4007. The ultra low residual diode switching noise is attenuated by the circuitry downstream anyways.
If you really want to overbuild the rectifier --- I'd think about full-wave bridge using one UF5408 per leg. You may get away with no bypass caps. Noise level from a UF5408 is pretty low.I have six in my 1968 Fender Bassman rebuild. Very reliable.
Good luck with your fix!
-----
Edits: 08/22/14
Well the idea was to change from a 5AR4 rectifier to solid state to allow myself to use a toroidal - cannot find any toroids with a 5v tap. And of course, not degrade sound quality in the process
But after considering having to series so many diodes and the cost of bypass caps I just went out and bought a new trans with a 5v tap and I'll use the 5AR4. Cost wise the toroid and all the caps and stuff will probably have cost as much if not more - and with my electronic skills, have resulted in a 911 call to put out the fire.
Moral of the story, sometimes a tube rectifier IS JUST more practical than solid state :-)
Thanks
Cleet
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