Question about filter cap in ancient amp.

[distorto]

I have a RicKenbacher black metal box amp that I am restoring. I ordered a 2uf 450 volt electrolytic as per the schematic in this link (first filter cap):

PersonalWebKit.com Web Site

Upon removal of the Cap I see that it is rated 500 volts. Does anyone know if I'll be alright with the 450? I'm having trouble finding a 2uf at any rating higher than 450. The other two electros I was able to get at the correct 500 volt rating.

I really appreciate any insight.

Thanks,

Chris

[Enzo]

The schematic says 450v, I have no reason to think it is not being truthful. They can always use higher voltages than needed, but not lower. Sometimes production supplies dictate using something out of the ordinary.

I imagine a 5uf might be easier to source.

[distorto]

Thanks a bunch Enzo.

[tedmich]

to a degree the voltage rating can be converted by shifting the operational lifetime. The super cheap "600VDC" axial caps seen on Ebay are likely identical to the more common 450VDC units but they are willing to put up with (and not list) a lifetime of <2000h at <85C.

See this Illinois capacitor lifetime calculator: Life Calculators - Illinois Capacitor

As an example, a crappy 3000h @ 85C rated 450v cap can be expected to give only a 10% shorter lifespan at 85C and 500v.

Does this mean I can run a 12,000h cap at 1.5x its rated voltage for 7,200h?
Hell no it may well 'spload!

More complex calculations are needed at bigger voltage differentials, see this CDE doc: http://electrochem.cwru.edu/encycl/m...4-appguide.pdf
so its not a "deal breaker" to have a quality cap run a little higher (~10%) than rated voltage, remember though temp is the key and that "metal box" looks like a worst case scenario temp wise!

The one at Weber looks like it was brought up by one of Bob Ballard's ROVs!

[gbono]

Thanks for the reference material on capacitors - I've always wondered how a capacitor manufactuer keeps an oxide from growing on the cathode aluminum film? The other interesting construction issue with aluminum electrolytics is there ability to act like a poor condenser microphone.

Also it would be interesting to use the calculator to see how many hours are left on some old power supply caps ;-)

[distorto]

Thanks for the caps info! Yeah, these metal boxes are beasts alright. Very cool though. I LOVE the giant Magnavox box capacitor! The 2uf Sprague takes up only a tiny fraction of space where the Magnavox resided. That should allow for a tad more airflow. The resistors are pretty whacky too. It took me a moment to figure out the color/value system. The resistor values in my unit are the same as in the unit pictured in the link above. They are slightly different from the schematic. Thanks again!

[bob p]

if you're faced with the problem of an insufficient voltage rating and an oversufficient capacitance rating, you might consider stacking the caps.

[tedmich]

if you're faced with the problem of an insufficient voltage rating and an oversufficient capacitance rating, you might consider stacking the caps.

a very good (and common) practice. 220k ohm equalizing resistors are the default but there are calculations for optimum values at Rifa and CDE

[distorto]

The amp is up and running and sounds great. Thanks for all your replies!