September 1942 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
Ode to a Power Supply? Well, maybe not really an ode, but this poem titled, "Power Supply," written by Eileen V. Corridan, appeared in the September 1942 edition of the ARRL's QST magazine.
It is really quite entertaining and instructive! It applies for the original tube-based circuit as well as for modern solid state versions. I somehow get the feeling that this poem will now be republished in many places.
by Eileen V. Corridan
The how and why of a power supply
Is something very quaint.
It takes the a.c. current
And makes it what it ain't.
You start with good ole a.c.
But you need some pure d.c.
How the PS finally makes it
Is now quite clear to me.
First, gimme a primary winding;
A secondary, too.
Now I've got a transformer
Let's see what it will do.
The primary takes the line juice;
Inductance does the rest.
But you gotta split the secondary
To do its job the best.
"Less turns in the coil for the heater,
More turns for the plate supply."
We've still got only a.c.
Which the tube will rectify.
Now we come to the moment
When tube and a.c. meet.
Just keep in mind a rectifier
Acts like a one-way street.
A.c. travels in wave form
From plus to minus, and then
It simply changes direction
And does it over again.
But the tube says, "Nothing doing
This is no swinging door.
I'll take one-half of your wavelengths,
One-half - and nothing more!"
At least a half-wave rectifier
Would act about that way.
We'll use another plate in there
And thus save wave and day.
So now one plate says, "Come ahead."
It takes its half-waves through
The other plate is minus, then;
It has no job to do.
Then comes along the other half.
The second plate starts working.
So half and half are now a whole
While number one plate's shirking.
From filament to filtering
The current that is flowing
Is now d.c. - pulsating kind
That toward the filter's going.
It isn't pure by any means.
Its ripples need some smoothing.
Chokes and condensers serve for this;
The waves find these quite soothing.
The filter circuit works like this:
In a condenser-input filter,
Inductance and capacitance
Keep pure d.c. in kilter.
Pulsating d.c. also has
Some a.c. current flowing.
Condensers short the a.c. out,
And chokes keep d.c. going.
And so at last like Ivory Soap
Our current's pure d.c.
I must confess this whole darn thing
Has made a wreck of me, see?
Posted March 21, 2011