Newbie at recapping questions
 

I just bought a new in the box 1953 vintage Admiral 5G31N AA5 radio on ebay. It is in need of recapping as it has a strong 60 hz hum. I have a schematic and found that it needs 2 electrolytics, a 30uf and a 50uf as well as 2 paper caps, a .05 and a .047. Here's the questions. With the electrolytics I found a 30uF @ 500V easy enough but can only find a 47uF to replace the 50. Would it be better to parallel 2 30's in place of the 50? I read somewhere that it is better to have more capacitance than less. Also in replacing the paper caps the .047 is easy to find but is that an acceptable replacement for the .05 or should I parallel a .0033 with a .047 to get up to .05? Also does anybody have any experience with F&T brand electrolytics from Germany? I would think that being from Germany they would be of decent quality but really have no idea. Thanks for the help. Photo of the radio is at the link.

http://www.flickr.com/photos/91751935@N00/7062447899/

There really ought to be a sticky thread about this sort of thing... this is a very common question.

Unless it's a special precision cap in a piece of test equipment or something, go with the closest modern value. Simple as that. A 30uf cap would be replaced with a 33uf, 50 goes to 47uf, 0.05 goes to 0.047, etc.

Old caps were usually marked with rounded values, while newer ones switched to using the same standard of values as resistors, I guess for uniformity. But it's really just a difference in the naming rather than a difference in the caps themselves... the marked value is simply a nominal one, there's also a tolerance to account for. For example, an average 47uf electrolytic cap with a +/- 20% tolerance could actually have a capacitance anywhere from about 38uf to 56uf. (Though in my experience they're more often on the higher side of the range than the lower.) And the tolerances on old caps was usually much looser than on modern ones, so an old 50uf cap could have an even wider spread.

As far as the F&T caps, they look to be some sort of 'boutique' capacitors aimed at the guitar crowd. I imagine they'd work just fine, but any of the supposed benefits of them would be completely lost on a cheapy AA5 radio anyway... you'd be much better off saving your money and just getting Nichicons, Chemicons or Panasonics from Mouser.

In general, the cheaper the better. That's how the radio was designed in the first place, and the design will accommodate a wide range without problem.

Having said that, replacing a 150V capacitor with a 500V unit isn't a good idea, as these type capacitors like to have nearly rated voltage applied. Otherwise they can get leaky and drift in capacitance quite a bit. So replace the 150V rating units with 150-200V rating.

The coupling and bypass capacitors are uncritical; the coupling capacitor actually determines the bass response, but those little speakers don't have bass response anyway.

Thanks for the help. I'm going to order 160V electrolytics now on your recommendation that I not go too far over the voltage rating of the original caps and 630V film caps to replace the paper. Thanks again for the help.

Good to know.
I have a big box of 220uf at 200v and I usually use one of those in an aa5 radio instead of the 2. Seems to work fine
Like you said they arnt very critical of anything.

I've heard that before, but I've never seen any actual data to back up such a claim. In fact, all the application notes I've seen from the major capacitor manufacturers show that to be untrue. Temperature matters, applied voltage does not (as long as it's under the rated voltage, of course).

That said, it's still usually a good idea to use something close to the original, simply because lower voltage caps are usually smaller and cheaper.

Thanks for the help everybody, I recapped the radio yesterday and had no problems. No circuit breakers were blown or caps exploded ;) The radio is playing nice and clear with great sensitivity. Thanks again.