[HAM] C-2 rebuild: can capacitors

[David Anderson]

Hi Malte,

You can use discrete (individual) capacitors for the power supply--no  
real downside to this method.

Or, check out Vibroworld's can capacitor selection:

http://www.vibroworld.com/parts/tech15.html

You may be able to find what you need, or if you look closely, you'll  
see that they can custom-make ones for you. I believe I had them  
custom-make a can capacitor for me for a Scott 299 integrated  
amplifier, but that was because space on the 299 chassis is very tight.

The values of power supply capacitance are not critical except for  
the first section attached to the rectifier tube. Too much  
capacitance attached to this tube will cause excessive current draw  
during each rectification cycle, leading to early failure. Make sure  
your voltage ratings are as high as or higher than the originals. In  
other words, if the original capacitor is 30uF, don't stress about  
using 33uf, or 47uF for 50uF. Electrolytic capacitors are not very  
precise in terms of value anyway. In the old days, I think they were  
+/- 20%.

Or, like George was suggesting, you can cut open the old cans and  
stuff them with modern electrolytics, but I've never been  
sufficiently motivated to go that route. Antique radio restorers do  
this, but they also melt out the insides of tubular paper capacitors  
and stuff modern film caps inside....... I'd prefer to know what I'm  
looking at, personally, rather than wonder if it's an old cap that's  
been re-stuffed or a new one.

Also, don't be surprised if the preamp sounds different after getting  
fresh power supply caps. Even if they haven't failed, these  
capacitors are far beyond their intended service life, and old power  
supply electrolytics can behave rather unpredictably and color the  
sound. The new ones should help restore the preamp to its original  
performance. Some people think that the power supply isn't "in the  
signal path," but this is not true.

David A.

On May 20, 2007, at 1:57 PM, Malte Rogacki wrote:

> Hello;
>
> this is my first post to this list (I was a member of its  
> predecessor about
> 10 years ago).
>
> I recently got my C-2 back from the studio where it had spent most  
> of the
> last decade and I'm attempting to rebuild the preamp (I'm also  
> tihinking
> about rebuilding the Leslie 122 but that's a different story...).
>
> Anyway, while I am able to find replacements for most of the "regular"
> capacitors I'm having a bit of a hard time tracking down the can
> capacitors. Now - given the fact that capacitors have gotten much  
> smaller
> in the meantime, would it make sense to just install single  
> capacitors if
> the space is sufficient? I think there is enough space inside the  
> AO-10 to
> accomodate those caps. Would there be any downside to this?
>
> (On a related note - the archive search is somewhat limited in
> functionality, it seems. Yes, I usually search the archives before  
> asking a
> question.)