What caps to order?

[Kingfisher]

I am about to order new electrolytic capacitors for my 1964 Panasonic clock radio, but some of the originals have weird values, like 5uf or 50uf. I could just go down to 4.7uf or 47uf but it appears Cornell-Dubilier makes the values I need. I would rather keep the original values in the circuit or go slightly higher. Has anybody ever used C-D caps for old radios or audio? Anyone know which is better "general purpose" or "computer grade"?

http://www.mouser.com/Cornell-Dubili...acitor&FS=True

[bandersen]

I'm sure the C-D caps would work just fine, but that's a lot of money for a cap. If you look at the data sheet for that $32 "general purpose", cap you'll see that it's really an industrial grade. Both the industrial and computer grade have rugged construction and high vibration resistance. Not something I'd be concerned about in a radio. Likewise the low DCL and ESR in the computer grade isn't something you really need.

So that leaves extended life as the only potential advantage I see. Unfortunately, I don't see any data on the life expectancy in the data sheet.

[Nick_the_'Nole]

C-D caps are good quality, but there's really no reason to use them over the much less expensive Nichicons and such. The difference between 4.7uf and 5uf, or 47uf and 50uf, is really just one of notation... the values on old caps were usually rounded off to whole numbers, while modern ones are standardized onto the same system of values that resistors use (which is a geometrical progression).

Notice the tolerances on those C-D caps... -10%/+75%, meaning the actual value of the 5uf cap could be anywhere between 4.5uf and 8.75uf. In standard capacitor values, it would probably be classified as a 5.6uf cap, perhaps even 6.8uf.

As far as grades of capacitors, computer grade is better quality, but completely overkill for use in radios and such. A modern 'general purpose' cap will be better than even a high-quality, low-noise cap from 50 years ago. I personally go with 105C low-impedance caps wherever possible, though, since they usually don't cost appreciably more than the standard grade caps anyway.

[Kingfisher]

So, dropping the cap value from 5uf to 4.7 or 50uf to 47 won't effect the sound quality of the radio? I had read on this site and AK that it is better to go a little higher than a little lower on capacitance values. Or won't it make any difference?

[Nick_the_'Nole]

The value of electrolytics in old radios is rarely all that critical, and the difference between 47uf and 50uf or 4.7uf and 5uf, is small enough to be inconsequential. It's well within the tolerances of the original cap. But there's nothing wrong with moving up a step, if you really want to... a 5.6uf instead of a 4.7, etc.

And yeah, increasing the capacitance can sometimes improve sound quality, depending on how the caps are used in the circuit. But you have to remember: you're working a clock radio... it's nowhere near hi-fi to begin with. Any improvements you make to the circuitry probably won't even be audible due to the limited frequency range of the little speaker in it.