Hi Andy,
The Electronicon caps are for industrial use. I got’em second hand in perfect condition via internet. They aren’t electolytes, they have no polarity.
I use similar sized 650VDC electrolytes of 1000 uF. Sure stores a lot of energy.
Regards, Gerrit
The Electronicon caps are for industrial use. I got’em second hand in perfect condition via internet. They aren’t electolytes, they have no polarity.
I use similar sized 650VDC electrolytes of 1000 uF. Sure stores a lot of energy.
Regards, Gerrit
Kemet makes 600-630 volt electros that I've used in amps with no problems. I really like the "hours" rating of the Kemet caps... 20,000+ hours! I don't know if that's accurate but that number sure looks good on paper! Time will tell...
i size my psu caps in such a way that no cap is ever over-volted in case the amp is powered on without the tubes inserted....
I guess that includes sizing within the allowed rating of 110% voltage for 30 seconds at power on?
It's been 8 years since the build so I don't remember all the details, but I do know I sized the balancing resistors based on the leakage current of the caps. The Mundorf film caps have much lower leakage current than electrolytics, so high resistance and low dissipation is to be expected. Last time I had the amps open a few months ago those resistors looked to still be fine; I inspect everything whenever I have them open since it's not often, due to their weight and good reliability to date.
Magz, most 0.4-0.5W resistors only have a 250V max rating, and some may get to 350V - is that what those caps have across them?
These are good film oil capacitors for high voltage applications.
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I used these 100uF 2000V in my 833A design
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This is manufacturer's site
I used these 100uF 2000V in my 833A design
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Like I said, I don't remember where I got them from 8 years ago but I'm sure they were higher voltage than that. I was very careful in selecting parts that wouldn't blow up in use, and so far they've held up quite well.
I built an UNSET board for experiments in the 600+ volts of B+ range.
I used a EPCOS 600 volt 47 uF cap, #B43541B8476M000 for the input cap.
I used a Kemet 630 volt 100 uF cap, #ALC70A101CC630 for the second cap.
These component choices were based primarily on what Mouser had in stock that would fit into an existing PC board. They worked fine and were briefly taken to 650 volts without incident.
When I decided to do some extended testing at 650 volts, I pulled the electrolytics and connected up some rather large 800 volt "UNLYTIC" Polypropylene caps that I bought on the swap meet here many years ago.
I was waffling between 425 volts of B+ into a 1500 ohm OPT VS 650 volts into a 5000 ohm OPT for roughly the same power level (30+ watts) from a single tube SE amp. I have settled on the lower voltage design for now, but I may eventually build both.
I used a EPCOS 600 volt 47 uF cap, #B43541B8476M000 for the input cap.
I used a Kemet 630 volt 100 uF cap, #ALC70A101CC630 for the second cap.
These component choices were based primarily on what Mouser had in stock that would fit into an existing PC board. They worked fine and were briefly taken to 650 volts without incident.
When I decided to do some extended testing at 650 volts, I pulled the electrolytics and connected up some rather large 800 volt "UNLYTIC" Polypropylene caps that I bought on the swap meet here many years ago.
I was waffling between 425 volts of B+ into a 1500 ohm OPT VS 650 volts into a 5000 ohm OPT for roughly the same power level (30+ watts) from a single tube SE amp. I have settled on the lower voltage design for now, but I may eventually build both.
OK, just to assuage your concern I went back to my build thread and, lo and behold, found this:
"I ordered these 1000V, 100M resistors for the decouplers, just to be safe:
Ohmite MOX300 Series
Should give about 8uA of current, plenty to swamp out the nA level leakage of the film caps."
The Kapton tape is rated for 8000V and there is a double layer, one on the chassis and one on the caps.
What max voltage do they have to withstand? Have you tested them since you made they amp, or is your test a visual check ?
The MOX300 have a max overload voltage of 1500V and a max pulse voltage of 3000V. Normal usage in my amps is ~750V each. I see no need to test components that show no sign of failure, other than with a visual check. I probably didn't even need them in the first place with those film caps but went for that extra level of assurance anyway.
Magz, sorry I missed your post #32 before when I posted #34.
It looks like the MOX300 range is now obsolete. The MOX300 datasheet is a little ambiguous in its specifications, as it refers to a "1000V voltage rating" but also refers to a Withstanding Voltage test of 500V for 1 minute, and an insulation resistance test of 500V (they appear to be performance tests with a defined limit of acceptable change).
In contrast the presently available MOX500 series changes its datasheet and refers to a Max Working Voltage as RCWV or 1kV whichever is lesser (but then it doesn't identify RCWV values for parts but that appears to be the rated power limit for a given resistance at the working voltage). The MOX500 part is 14.5mm long body whereas the MOX300 has a 9mm long body. In comparison a typical 0.5W MF parts is circa 10mm body length.
I'm just making the comment that it is pretty demanding to get a resistor part with a short body length also with a 1kV working voltage rating, and maybe modern standards have caught up with even the quite special MOX300 series.
Even measuring 100Megohm is at or above the limit of many DMMs, and would typically require an insulation resistance meter.
In a voltage balancing application where the film caps have negligible leakage current compared to the bypass resistors, if a bypass resistor fails to a lower resistance (such as creepage resistance across the body skin, or internally) then the other film caps may be exposed to the total string voltage (as well as the other balancing resistors being exposed to the higher voltage). The hassle is that the operating voltage across each cap can't be measured, as the measurement will likely radically change the voltage balance.
It looks like the MOX300 range is now obsolete. The MOX300 datasheet is a little ambiguous in its specifications, as it refers to a "1000V voltage rating" but also refers to a Withstanding Voltage test of 500V for 1 minute, and an insulation resistance test of 500V (they appear to be performance tests with a defined limit of acceptable change).
In contrast the presently available MOX500 series changes its datasheet and refers to a Max Working Voltage as RCWV or 1kV whichever is lesser (but then it doesn't identify RCWV values for parts but that appears to be the rated power limit for a given resistance at the working voltage). The MOX500 part is 14.5mm long body whereas the MOX300 has a 9mm long body. In comparison a typical 0.5W MF parts is circa 10mm body length.
I'm just making the comment that it is pretty demanding to get a resistor part with a short body length also with a 1kV working voltage rating, and maybe modern standards have caught up with even the quite special MOX300 series.
Even measuring 100Megohm is at or above the limit of many DMMs, and would typically require an insulation resistance meter.
In a voltage balancing application where the film caps have negligible leakage current compared to the bypass resistors, if a bypass resistor fails to a lower resistance (such as creepage resistance across the body skin, or internally) then the other film caps may be exposed to the total string voltage (as well as the other balancing resistors being exposed to the higher voltage). The hassle is that the operating voltage across each cap can't be measured, as the measurement will likely radically change the voltage balance.
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I just got some great 600v 75uf poly caps from Apexjr. They are the best inexpensive option for higher voltage ps caps. The only thing is they have short leads but who care at this price? No affiliation just a happy customer. He’s also got tons of silver Teflon wire of all gauges, colors, and solid or stranded. He’s on the bay.
All the wires are silver plated copper, unfortunately. It would be nice to have solid silver core.