[ARC5] Disc Capacitors

[Geoff]

----- Original Message ----- 
From: "Bill Cromwell" <wrcromwell at gmail.com>
To: <arc5 at mailman.qth.net>
Sent: Sunday, March 03, 2013 10:21 AM
Subject: Re: [ARC5] Disc Capacitors


> On Sun, 2013-03-03 at 09:50 -0500, wb3fau55 at neo.rr.com wrote:
>> Don't use  diameter as a rule of thumb  to determine unknown voltage 
>> rating.  There  have been
>> some  pretty bad dielectric materials used in past.  Ceramics and epoxies 
>> are very good.
>> Some plastics from  years ago not too good.  Unless it is  marked as 
>> rated  for 500v, I would
>> not use it on high voltage.  73 Russ.
>> ---- Robert  Eleazer <releazer at earthlink.net> wrote:
>> > I have some .01 mfd caps that are not marked as to max voltage 
>> > capability.  They are pretty good size, at least a half inch in 
>> > diameter, maybe more.  I also have a bunch of .01 mfd caps that are 
>> > marked "50V" and are no more than 3/16 inch in diameter.   I need some 
>> > that are good for at least 500V.
>> >
>> > Does anyone know a good rule of thumb for diameter versus voltage 
>> > relative to disk caps?  Bigger means higher voltage; that follows 
>> > logically, since you need more insulation, but what kind of a estimate 
>> > can we make based on size?
>> >
>> > Thanks.
>> >
>> > Wayne
>
> Hi,
>
> I have a drawer full of disc caps that do not have voltage ratings on
> them. I consider the manufacturers being too ashamed of their products
> to put their name or voltage rating on them. I will use them in 12 volt
> solid state circuits and save the real ones for my tube circuits at
> higher voltages. properly rated and *marked* caps are available at very
> reasonable prices from multiple online sources.
>
> 73,
>
> Bill  KU8H


  For high volume radios and TV's most manufacturers didnt bother with 
unnecessary information on their caps, they ordered huge quantities and as 
long as assemblers knew what to grab that is all that mattered.

Service shops could consult SAMS if they had a need to know more but I doubt 
it happened much as they could care less. A .01 was a .01 for 99 44/100% of 
the time

Same with low priced sales outlets, they bought the same, often mfg 
overstocks or part of the same production runs as the equipment 
manufacturers. Since the early 50's the .01 500V was about 1/2" in diameter 
and unmarked except for value and maybe a logo or just a part # such as 
Zenith used. When standards evolved more info was added.

Ive treated those unmarked .01's and the slightly larger .05's as 500V for 
decades and have used in all sorts of 200-300V non critical circuits without 
even a hint of failure. As mentioned, higher voltage ones are thicker and 
Ive yet to see any 1000V or higher that were not marked.

Carl