[sdiy] Re: Learning electronics (was Polyevolver)

[Roy J. Tellason]

On Wednesday 20 April 2005 07:05 pm, Bob Weigel wrote:
> The resistors with 'different background colors' are...in all likelihood
> capacitors also :-). 

Unless you're talking about the difference between brown body and blue body 
(flameproof) resistors.  But yeah,  those light green ones are indeed caps.

> Some caps have been produced which have a more
> glassy looking finish and are shaped and striped in similar form to
> resistors.
>    Some glass looking capacitors are high stability caps that are often
> used in oscillator circuits and the like.  I have a big bag of 390pf's
> in stock I seem to recall.  Usually fairly fine wires coming out of the
> glass case with a label wound inside.

The ones I've bumped into the most were 100nF,  and used as bypass caps for 
logic and such.

> Actually the dielectric material used is polystyrene in these though.

I thought it might be.

<...>

> They don't fail too often unless they get smashed :-).  In most cases
> where they are used you can substituted a ceramic or mica type,
> especially in an audio circuit.

I wouldn't substitute ceramic for places that didn't use it in the first 
place,  or vice versa.  Too many circuits are going to be sensitive to the 
parameters of ceramic caps that change wrongly for the circuit in question.

One time I was playing around with a 567 chip,  just to see what it could do.  
Worked all the formulas and such and did the same with a 555 to give me a 
tone at the same frequency,  and it didn't work.  Then I took out the ceramic 
caps and put other types in there and it worked.

S/H is another area where the parts might be sensitive.