XPost: rec.antiques.radio+phono, sci.electronics.repair   
   From: wrongname@nospam.com   
      
   On Wed, 09 Aug 2017 04:54:25 -0700, Big Bad Bob wrote:   
      
   > On 03/09/17 17:01, oldschool@tubes.com wrote:   
   >> What type of capacitor would be the best match to replace the old   
   >> paper/wax caps in old tube gear?   
   >>   
   >> I am not referring to the electrolytics, those I know need to be   
   >> electrolytic caps. I am referring to the inter stage caps, such as .01   
   >> .05 .1, .005 and so on.....   
   >>   
   >> The object is to replace all the caps in an old tube radio, or any   
   >> other tube stuff.   
   >   
   > well, if you must replace them with more modern components, a decent   
   > ceramic capacitor should do fine.  From what I have seen, ceramics were   
   > common in gear made in the 50's and 60's because of their small relative   
   > size and reasonable consistency in manufacturing.   
   >   
   > You should be able to order them from companies like Digikey, Mouser,   
   > etc..  Just make sure the voltage ratings are high enough, and you   
   > should be ok.   
   >   
   > I've seen on-line "photo piles" of before/after restoration efforts in   
   > which modern components were "hidden" inside of hollowed-out components.   
   >   Maybe you can stash a modern ceramic inside of the paper/wax tube, and   
   > seal it up with a bit of hot glue...   
      
   It will be tough to find good ceramics in the values listed with voltage   
   ratings high enough for tube gear.  Polyester (Mylar) or Polypropylene   
   are better choices.   
      
   As for the quality of ceramic capacitors, it depends on what kind of   
   ceramic is used.  C0G ceramics are about the best capacitors you can   
   easily get.  They are very stable, have very low loss, and are excellent   
   in just about every other way.  The one way they are not excellent is   
   that, except for low values (less than around 1000pF - depends on   
   manufacturer) they are large and expensive.  Mid grade ceramics like X7R   
   are less stable and less expensive.  They are suitable for most audio   
   frequency work.  The really bad ceramics are the ones like Z5U.  They are   
   truly horrible in most ways and are suitable only for non-critical   
   circuits like supply bypassing.  They are, however, tiny and very cheap.   
   Go to the manufacturer's data sheet for the capacitors you want to use to   
   see if their characteristics match the application.   
      
      
      
   --   
   Jim Mueller wrongname@nospam.com   
      
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