I am going to be doing three different amp projects. one is a recap of an older tube amp in a Sony TC-200 (first version), recap a working mono Philips 4 track unit and the third is my 6BM8 Push Pull amp (Fire and Ice).
I need to buy caps for all three. but I only want to deal with one set. the caps I was told it is fine to go with higher than the rated voltages. in the TC-200 it shows that for the power supply filter caps are 3 100uf 180WVDC whereas in my tube amp (fire and ice) caps are needed at 300VDC ( 25uf, 25uf and 40uf))
Here is my question. is it wise to use higher WVDC caps in a circuit? One guy says no as the electrolytic won't be stable. Another says "Not a problem". I want to order the needed caps for the projects in larger quantities. Oh yeah, in my philips tube reel amp they are 35uf, 35uf and 50uf at 350WVDC. therefore I was looking to getting 400-600WVDC instead of having lots of voltage versions.
I need to buy caps for all three. but I only want to deal with one set. the caps I was told it is fine to go with higher than the rated voltages. in the TC-200 it shows that for the power supply filter caps are 3 100uf 180WVDC whereas in my tube amp (fire and ice) caps are needed at 300VDC ( 25uf, 25uf and 40uf))
Here is my question. is it wise to use higher WVDC caps in a circuit? One guy says no as the electrolytic won't be stable. Another says "Not a problem". I want to order the needed caps for the projects in larger quantities. Oh yeah, in my philips tube reel amp they are 35uf, 35uf and 50uf at 350WVDC. therefore I was looking to getting 400-600WVDC instead of having lots of voltage versions.
It's both wise and recommended. Be conservative (about voltage and temperature ratings).
All good fortune,
Chris
All good fortune,
Chris
Modern electrolytics are much more stable than those of yore and operating a high voltage cap on a significantly lower voltage should not cause an appreciable reduction in capacitance.
As long as proper voltage derating guidelines are followed the real cap killer is temperature. 105C types will generally live a lot longer at any given operating temperature than a device rated for 85C. (And a 10C reduction in cap temperature doubles life - so keep as cool as possible.)
As long as proper voltage derating guidelines are followed the real cap killer is temperature. 105C types will generally live a lot longer at any given operating temperature than a device rated for 85C. (And a 10C reduction in cap temperature doubles life - so keep as cool as possible.)
And what are these guidelines exactly? As for "keeping cool" the Phillips is a plastic heat box 🙁 I don't think I can do much about that. Sony has a good air flow as would my amp design. Yes, I am speccing 105c parts
The manufacturer will generally provide derating guidelines in the data sheet or an app note - if not I would not exceed 80% for an aluminum electrolytic.
Okay so a 400wvdc cap at 160 would be okay as using the 70%. Or 280 means 120vdc would be the "floor"
Cornell Dubilier say 50% voltage derating is common in space and military applications because it extends capacitor life. So obviously no harm in using a higher rated cap at lower voltages.
The only time to worry is if the ripple current is very high and a higher voltage cap is replaced where a same size but lower voltage cap has been used. The higher voltage rated cap will have lower capacitance and probably lower ripple current rating. This isn't applicable in your situation.
I read some paper by a chemist that using an electrolytic at lower voltages for a long time, essentially created a new rating for that cap. The cap would need to be reformed if it were to be reused at higher voltages.
The only time to worry is if the ripple current is very high and a higher voltage cap is replaced where a same size but lower voltage cap has been used. The higher voltage rated cap will have lower capacitance and probably lower ripple current rating. This isn't applicable in your situation.
I read some paper by a chemist that using an electrolytic at lower voltages for a long time, essentially created a new rating for that cap. The cap would need to be reformed if it were to be reused at higher voltages.
Just a thought,
If your caps are close to working voltage and you have a heater supply fail or your fuses are after the caps on the HT rail. Then the increase in the B+ with no load could exceed the WV of the caps creating a capacitor blow out. I don't think you should ever have less than B+ off load working voltage.
Regards
M. Gregg
If your caps are close to working voltage and you have a heater supply fail or your fuses are after the caps on the HT rail. Then the increase in the B+ with no load could exceed the WV of the caps creating a capacitor blow out. I don't think you should ever have less than B+ off load working voltage.
Regards
M. Gregg
+1Especially if you cannot entirely rule out that you will create off-load conditions in case of a failure (and in most cases you cannot rule this out).
Easier to buy a higher voltage cap (or use them in series) than to remove all that gooey junk in your precious amp after a blow-up.
Martin
In the first post he says the highest value cap to be replaced is now 350WVDC. He plans to get 400WVDC caps. So isn't he covering his *** pretty good?
Yes, it seems so.
It might be worth to check what kind of ripple current they have to expect in the power supplies of these three amps and see if these particular 400 WVDC caps are up to the task.
One minor issue is the difference in ESR for higher voltage rated caps. The higher the voltage, the greater the ESR as a general rule.
Personally, I would measure the voltage with all the tubes removed, and high line applied via a variac. Then I would pick the cap with closest higher rating and a surge rating of at least 50V above that voltage. I would also check in the mfg data sheet to compare ESR and ripple current ratings of it and the next higher voltage rated cap.
Personally, I would measure the voltage with all the tubes removed, and high line applied via a variac. Then I would pick the cap with closest higher rating and a surge rating of at least 50V above that voltage. I would also check in the mfg data sheet to compare ESR and ripple current ratings of it and the next higher voltage rated cap.
One more thing....
Higher voltage rated caps are physically larger than lower voltage rated caps of the same uf, so confirming that they will fit before you pull the trigger on the order is a good idea. Also, many caps are available in two different form factors, tall & skinny or short and fat, which helps when squeezing them in.
Higher voltage rated caps are physically larger than lower voltage rated caps of the same uf, so confirming that they will fit before you pull the trigger on the order is a good idea. Also, many caps are available in two different form factors, tall & skinny or short and fat, which helps when squeezing them in.
Caps also come in radial and axial which on point to point circuits Is nit a big deal.
Which is a big deal on the Sony as it has a pcb and the solid state section is Densily packed.
It won't hurt the caps to run at lower voltage, but higher voltage electrolytics have higher ESR and higher leakage current. These can be issues for example in DC blocking applications.
Jeez guys. I know we are nerds, but give the nitpicking a break! She's recapping a Sony and Philips, both good brands that used good engineering. If the amp had 350VDC caps, well dont mix in a bunch of ametureish BS and claim she need to check this and that and then add a stupid margin. Get 350VDC caps and be done with it.
The only thing is you dont want to over do the capacitance in the higher voltage amp, and you dont want less in the lower volt amp. So it might be difficult, and cost more, to cram enough smaller valued caps in the lower voltage one. Not sure you are doing yourself a favor here.
What is the b+ in your 'Fire&Ice' amp?
The only thing is you dont want to over do the capacitance in the higher voltage amp, and you dont want less in the lower volt amp. So it might be difficult, and cost more, to cram enough smaller valued caps in the lower voltage one. Not sure you are doing yourself a favor here.
What is the b+ in your 'Fire&Ice' amp?
250wvdc it is based on a push pull 6bm8 design. As for the others I plan to stick with the original uf values.
I agree,
However I think the comments are based upon the title of the thread..
(Capacitor WVDC is higher really better?)
And this is linked to a DIY build.. nothing wrong with a higher working voltage in the now smaller package than was available back then..if it will fit.
Regards
M. Gregg
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You can see near off-load conditions at start up depending on which rectifier tube is in play and your heater circuits. I monitor voltage at start up and use caps that are rated above it. Just make sure you are looking peak values not RMS. I haven't had the blown cap experience yet, I would prefer to read about it. Still a newbie!
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