[ARC5] replacing C3 and C8 of BC453A

[Richard Knoppow]

On 2/1/2015 7:35 AM, J Mcvey wrote:
> If you ever have any doubt what the composition , value or tolerance 
> of the caps might be, the original military manuals are quite specific.
>
> I am presently working on a BC654 where I encountered several white 
> hollow tube capacitors marked .008 . The manual said they were mica. I 
> suspect that they were, since the couple random samples I took out to 
> test were still  the correct value and had virtually no leakage.
> That saved me the time and money to replace them. Others that had 
> large rectangular plastic cases LOOKED like mica types but were listed 
> as paper. Sure enough, these were very leaky.
>
> BTW, as a military piece, I found the BC654 to be a disappointment on 
> many levels...or maybe I just have a natural prejudice against 
> floating ground series string sets...??? It's also very difficult work 
> on or test in a disassembled state.
> Perhaps the army wanted a no-frills, easy to operate short distance 
> radio, and that's exactly what they got!

        I think the caps you found were ceramics.  AFAIK mica is not 
flexible enough to form into tubular form.   Class-1 ceramic caps are 
very stable unlike Class-2, they use a  different dielectric. Flat paper 
caps were made by Micamold, Solar, and probably others. Those with the 
dot code for value have a white dot to indicate paper while mica caps 
have a black dot.  This is often shown in the identification charts in 
military handbooks.   I don't know much about the original 
characteristics of the flat paper caps but evidently they were good 
enough at RF to be used to replace mica caps when mica was in short 
supply.  As a side note the Micamold caps I've dissected were all quite 
well made while a number of BB and other conventional caps had distorted 
windings.  I don't know if the distortion was from some adjustment 
procedure before molding or if the molding process caused it.