[GreenKeys] Teletype Model 15 power Q's...

[Jeffrey D Angus]

On 11/9/2016 1:45 AM, epvgk at limpoc.com wrote:
> For the sake of experimenting, my loop here craps out below
> about 40-50v.
This is basic "Electronics 101."
My first TTY machine was a Model 15 in 1972.
And my thought at the time was "Why are we using 120 volts when it
only takes 12 to pull the selector magnet in?"

John, my college electronics professor had this beautiful wooden chest
on his table. "The SECRET OF RADIO", and if you showed promise in his
class, he'd make a big deal about unlocking the chest and letting you
peek inside.

He showed me one day. As he raised the lid, there before my eyes was
the secret. A large mica transmitting capacitor, a pie-wound choke and
a 10 watt Ohmite resistor. And I had to laugh. He was absolutely right.

One of the little things we were told to help us remember how all this
works was the phrase "Eli the ice man."
Voltage leads current in an inductive circuit.
Current leads voltage in a capacitive circuit.

To impress a square wave across a capacitor it takes a voltage source
with an infinite current capacity.
To impress a square wave across an inductor, it take a current source
with infinite compliance (voltage.)

The mechanics of the selector magnet is just that. It is a magnet. It
takes current to make the magnetism that actuates it. And to get it
to do that, it requires a lot of turns. This equals inductance. Roughly
4 Henries of inductance.

Whether it's 12 volts and 200 ohms, or 120 volts and 2000 ohms,
this is a current source. The question is which voltage will allow the
current to rise to 60 mA quicker.
And the faster the current rises to 60 mA, the faster the selector
actuates.

This isn't rocket science people.




-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com