wrote in :


On Tue, 29 Jan 2008 14:28:10 +0000 (UTC), bz
wrote:

wrote in :

My favorites were the Mica Capacitors. I'm still wondering how they
were made, and how were the wires attached? I just liked the look of
them with all the colored dots on them. Listed on site below as well
as pictures of them.
http://www.sayedsaad.com/fundmental/...0Capacitor.htm

In an article (below), they mention the Silver Mica caps (which came
out later). It says they were plated. How does one plate mica? And
how does one get the right thickness of mica, knowing how it's all
random pieces.

I made ceramic capacitors in the late 60's and early 70's for Sprague
Electric co. so I can make some guesses as to how the micas were made,
or tell you how I would do it.

Mica comes in large sheets that are rather uniform in thickness.
I would use a chemical reaction http://www.finishing.com/0400-
0599/415.shtml to plate the mica on both sides and measure the
capacitance of the large sheet.
From that value, I would know what sizes to cut the sheet into in order
to make many mica capacitors of 'about the desired value'.

I would then cut the sheet up into a bunch of small capacitors, solder
on leads, and then use injection molding to make the case.

Of course, each finished capacitor would be tested for value and the
actual value put on the case.

We did something rather similar when making ceramic capacitors. We had a
target value for the batch we were making, used silk screen printing to
print patterns of electrodes onto a layer of green[unfired] ceramic
laid down another layer of ceramic slip, printed more electrodes,
continued until we had enough 'area' to give the desired cap. We would
then break up the sheet into hundreds of 'green' capacitors, 'fire' them
in a kiln, abrade the edges to expose the electrodes, dip the ends in
conductive ink and bake it on, solder on leads and cover coat.
We would then test them for value and stamp them.

But the article does not mention the make-up of the
original Mica Caps.

http://www.radio-electronics.com/inf...citor_types.ph
p

And what the heck is Tantalum?

An element. A metal. Right under Niobium and Vanadium in the periodic
table, between Hafnium and Tungsten.
It can be used to produce a rather high value electrolytic capacitor as
aluminum is still used for some electrolytic.


Thanks for the info. I always wondered how they made the caps. I
never thought they would be made in sheets, and thought each was made
separately. I did suspect that they would be tested to insure
reliability. I'm sure none of them would be 100% accurate if made in
sheets like that, plus the mica would be less likely to be accurate
compared to the man made ceramics. I would imagine most of the lead
soldering and cutting would all be done by machine, right?

The leads were cut to length and taped to a cardboard carrier.
There might be 20 or so pairs of leads per carrier strip.
The carrier was placed in a jig and the chips were hand loaded.
A spring held the leads against the chip and the friction between chip and
leads kept the chip in place while the jig was lowered through a layer of
hot oil into the molten solder.

For some parts, the chips and leads were in a jig that carried them over a
fountain of molten solder (wave soldering machine).


I never learned much chemistry, I just looked up Tantalum on
wikipedia. I never heard of that as a metal.

Now I am thinking how they make resistors. I'll assume they are made
in long strands, sort of like spaghetti and cut up. But how they
attach the leads to a piece of carbon is another thing.

We made our resistors by silk screen printing an organo-metallic ink onto a
ceramic substrate.
They were then passed through a kiln, where the organic materials burned
away, leaving a thin-film resistor.

Now-days, vacuum deposition is used to make most metal film resistors.

I don't know how carbon resistors are made, sorry.

An interesting feature of a resistive film is that it has a certain
resistance in 'ohms per square'.

It doesn't matter WHAT size the square is. [power rating DOES depend on
size, but not resistance].

If you want higher resistance, you make the resistor LONGER. If you want
lower, you make it WIDER.



Thanks again, interesting information.


Learning is fun. Have fun!



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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