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Re: why aren't electronics schematics trade secrets?

From: Roger Johansson
Subject: Re: why aren't electronics schematics trade secrets?
Date: 3 Dec 2004 14:30:31 GMT
User-agent: Xnews/4.06.22

>> I remember forty or so years ago, we got a stereo and the schematic
>> was actually pasted on .....  

I disassembled several radio-gramophones when I was a child.

Big furniture floor types and slightly smaller desk models.
Those radios usually had many shortwave bands, and anything from 1 to
6 tubes, and often a circuit diagram inside.

What surprised me were the ingenious half-mechanical solutions which
showed up in those radios. 

One was using a piece of cottom string to pull a coil further away from
another coil, changing the degree of magnetic coupling between them,
probably changing the characteristics of a filter. 

Another was a lever to move which moved a metal foil on top of another
metal foil, a variable capacitor. Movable coil cores to change the
inductance, etc.. 

Today we see very little of mechanical movement in machines, we hardly
have real switches anymore, just plastic buttons which move half a
millimeter. And all circuits which needed mechanical movement have been
replaced with full-electronic variants. 

The last to go in consumer electronics was the variable capacitor in

Roger J.

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