October 1960 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Before there were clocks that synchronized themselves to a wireless
low frequency (LF) time standard
emanating from one of
NIST's broadcast towers, a different method was used to
keep all the clocks in a building (like a school) reading the
same time. Many of the AC-powered mechanical master-slave clock
systems are still in use today. This episode of Carl and Jerry
has them teaming with a contract repairman to figure out why
seemingly random clocks in their high school failed to synch
with the master overnight. Author John T. Frye provides
a pretty thorough overview of how the system operates using
a power line carrier scheme. Of course the boys' keen troubleshooting
skills come to the rescue of the poor, beleaguered repairman.
I still remember watching in awe one time in elementary school
(c1960s) when after the end of a power failure during the school
day the wall clock at the front of the room began racing ahead
seemingly magically until it stopped at what was presumably
the correct time. If I was the teacher, I would have told the
kids that it was the hand of God adjusting the clock, and that
He was watching them to administer swift punishment if anyone
got out of line - that's why I'm not a teacher ;-)
Carl and Jerry: The Crazy Clock Caper
By John T. Frye W9EGV
It was almost the end of an exasperatingly beautiful, warm,
sunny school day. Carl and Jerry were sitting in class listening
impatiently to the voice of the Latin teacher droning on and
on about the second conjugation. Their eyes were on the clock
over the door.
Suddenly the voice of the principal issued from the intercom
speaker: "Miss Manders, will you please have Jerry Bishop and
Carl Anderson come to my office at once?"
The boys rose from their seats at a nod from Miss Manders
and started for the door. They could feel the backs of their
necks growing hot under the concentrated questioning stares
of their classmates.
"Now what've we done?" Carl muttered as they walked along
"Rather: what have they caught us at?"
Jerry knocked at the office door, and the sight of the principal's
smiling face banished their worries.
"Boys, this is Mr. Stoner from Center City," he said. "Mr.
Stoner is here to straighten out a little trouble we're having
with our new automatic clock and bell system."
Tall, thin, bespectacled Mr. Stoner stopped his nervous pacing
about the office long enough to shake hands.
"He needs a couple of boys to help him with his testing,"
the principal explained. "I suggested you two because of your
interest in electricity and electronics. I have to leave for
a board meeting, but I'm sure you three can get along without
my help - especially since my wife says I can't even plug in
the electric toaster and do it right!"
As the principal closed the door behind him, Mr. Stoner slumped
into a chair. Nervously tugging at his ear, he stared searchingly
into the faces of the two boys. Finally he spoke:
"Boys, I'm going to level with you. I'm in a spot. Actually,
I'm an electric typewriter serviceman. The man who is supposed
to take care of these clocks is on vacation, and I'm pinch-hitting
for him. I know just a little about the system, but that little
doesn't seem to be enough to find the trouble. I've spent three
days on it, and my boss is beginning to ride me. He thinks a
man who can fix electric typewriters should be able to fix anything.
On top of that, my wife called last night and said that my little
boy is sick - I should be home with them.
"The principal tells me you two are sharp on electronics.
I hope he's right, for I certainly could use some help."
"What's wrong?" Jerry asked.
"All the clocks in the building are supposed to keep in step
with the master clock here in the office," Mr. Stoner replied,
as he sprang up and renewed his pacing. "Every fifty-ninth minute
this master clock causes an audio tone of a certain frequency
to be fed into a power amplifier located there in the closet.
The signal is built up to about forty watts and fed into the
117-volt a.c. line. It goes out over the power lines to the
electric clocks plugged in in the various rooms.
"Inside each clock is a transformer with tuned windings.
The primary in series with a capacitor is connected directly
across the a.c. line. The coil and capacitor are series-resonant
at the audio frequency, so maximum current flows in the primary.
Audio voltage developed across the parallel-tuned secondary
fires a cold-cathode thyratron tube. Current through this thyratron
actuates an electric clutch that causes the sweeping second
hand to pick up the minute hand and carry it to the vertical
position before dropping it. Every twelve hours a similar arrangement
corrects the hour hand.
"In some installations the correction takes place at 6 a.m.
and 6 p.m., but the hour hand is corrected at noon and midnight
in this setup. Different audio frequencies are fed into the
line by the clock at preset times. These signals are picked
up by other tuned transformers with thyratrons that close relays
and ring bells in the classrooms. By using different frequencies,
the bells of different rooms can be rung at different times
so a complex time schedule can be accommodated.
"Every morning several of the room clocks indicate the wrong
hour. Others are on time. Different clocks are incorrect on
different mornings. At noon they are all automatically corrected,
and they stay on time until school is out. But the next morning
it's the same old story."
"What have you done so far?" Carl wanted to know.
"I've checked the tone generator and the power amplifier
thoroughly. All the tones are on frequency, and there's no parasitic
oscillation or noise in the amplifier. I've checked the tuning
of the transformers in the clocks to make sure they're right
on frequency. I've gone over the wiring. And I've measured the
clock-setting signal at all the clocks - it's supposed to be
in excess of 0.8 volt, and it is.
"Incidentally, the coupling between the primary and secondary
of each tuned transformer is variable so that the voltage delivered
to the thyratrons can be kept uniform in spite of different
audio voltage levels present across the wall sockets into which
the clocks are plugged. Since the audio signal must thread its
way through the maze of a.c. wiring and be subjected to various
bypassing actions of different loads on different parts of the
wiring, it is understandable that these levels would be different."
"It's kind of funny that nothing happens during the day,"
Jerry mused. "Maybe something the janitors do at night upsets
"I thought of that. The only electrical apparatus they use
regularly is a power vacuum sweeper. When the vacuum is running,
it produces some noise on the line, but this noise only measures
0.2 volt - far too low to trip the clock-setting mechanism.
Oh, yes, there's one odd thing the principal noticed: more clocks
seem to go crazy when it rains. That would point toward humidity
as the cause of our trouble, but I can't imagine how."
"Do you have any other ideas?" Carl wanted to know.
"Just one. Today I figured that line voltage variation occurring
at night might somehow upset things, so I borrowed this variable-voltage
transformer from a TV shop. I'll crank the voltage applied to
the signal generator and the power amplifier up and down while
you two check the clocks in various rooms to see if anything
Carl and Jerry went from room to room inspecting the clocks
while Mr. Stoner raised and then lowered the line voltage applied
to the clock-regulating equipment by ten percent. The clocks
"Well, there goes my last idea," Mr. Stoner said dispiritedly
as the boys came back into the office. "I just don't know -"
He was interrupted by the ringing of the telephone on the
desk. He answered it, and the boys could see him becoming more
and more agitated as he talked.
"My little boy has just been taken to the hospital for an
emergency appendectomy," he reported as he hung up the telephone.
He began gathering up his tools and throwing them into his tool
box. I must go home at once. Have the janitor lock the office.
I don't know when I'll get back." This last sentence was shouted
back over his shoulder as he dashed out the office door.
Carl and Jerry hunted up the janitor and delivered the message,
then started for home.
"You know," Carl remarked, "I feel sorry for Mr. Stoner.
He really has trouble. I wish we could help him."
"Maybe we can," Jerry answered. "Let's go to school a half
hour early tomorrow and check those clocks ourselves. We just
might get lucky and stumble onto something."
The next morning the boys found only seven of the forty-one
clocks with the incorrect time. Two were in the basement, three
on the first floor, and two on the top floor.
Shortly before noon it began to rain, so Carl and Jerry ate
lunch in the school cafeteria. As they ate, they puzzled over
their problem. "It simply has to be something that happens between
midnight and morning," Jerry finally decided. "Suppose we ask
the principal to let us snoop around here tonight and see what
The principal readily agreed to the plan and gave the boys
a pass key that would let them into any of the classrooms. The
sensible thing would have been for the boys to go to bed right
after supper and get some sleep before midnight, but what did
our heroes do? They stayed up and watched the late show until
a quarter of twelve! Then they set out for the school, Jerry
carrying an a.c. voltmeter, and Carl a pair of binoculars.
Quietly, they let themselves into the dimly-lit building.
There was something spooky and a little sinister about the empty
halls and the closed doors of the classrooms. From somewhere
in the building came a faint humming sound, and they moved softly
about in their sneakers until they located it. The hum was coming
from the large tank of an industrial vacuum sweeper which was
sitting on a low cart in front of an open door.
As the boys peered around a corner, the janitor came out
of the room and piled the long flexible hose of the vacuum cleaner
on the cart, recovered the line cord that had been plugged into
a socket in the room, and pushed the cart to the next door.
It took the janitor only a few minutes to vacuum this room,
but he apparently decided that the floor of the next one was
too dirty to be dry-cleaned. First he sloshed sudsy water over
the floor and gave it a quick going-over with a rotary wet mop.
Then he used the vacuum to suck up the excess water. As he did
this, the boys could hear the motor of the cleaner slowing down
in protest. Finally, he went over the floor with a clean mop
and clear water.
Jerry silently beckoned Carl into a classroom across the
hall. The floor was still damp, and the clock was four hours
"I've got an idea," Jerry whispered. "You take the key and
get into that wing across the way where you can see the clocks
in the rooms the janitor is cleaning. Don't let him see you.
I'll be doing some checking here. We'll meet in this room in
half an hour."
Carl waited until the janitor had started on another room
and then slipped away.
Jerry tiptoed across the hall to a baseboard outlet socket
just outside the room in which the janitor was working. There
he plugged in his own version of a tuned transformer he had
made from an old TV flyback transformer. Placing his voltmeter
across the secondary of this transformer enabled him to read
the voltage of any clock-setting signal on the line without
interference from the 60-cycle a.c. current.
When the janitor switched on the vacuum cleaner, Jerry got
a reading that represented 0.2 volt; but when the sweeper began
to suck up water, this reading quadrupled! With a smile of satisfaction,
Jerry unplugged his apparatus and returned to the rendezvous
room to await Carl.
The latter soon appeared, his eyes wide with excitement,
and his uncased binoculars dangling about his neck. "When that
vacuum sweeper begins to suck up water, the clock in the room
goes crazy," Carl reported.
They did not discuss the matter further. It was two o'clock,
and both boys were growing very sleepy. They slipped out of
the building and went straight home to bed.
When Carl and Jerry arrived at school the next morning, Mr.
Stoner was standing on the steps, smiling and relaxed.
"The little boy is getting alone fine," he said, "and I feel
like a new man. I guess I needed a shock to show me what was
really important. Now that my son is going to be all right,
nothing else bothers me. We'll lick this clock thing in time,
and I refuse to get worked up about it again."
Excitedly, both boys talking at once, Carl and Jerry told
him what they had observed the previous night.
"That's it!" Mr. Stoner exclaimed. "The vacuum cleaner was
only sucking air when I checked it. When it sucks water, the
motor works harder and produces a noise of the right amplitude
and frequency to trip the clock-setting mechanism in the room
where the vacuum sweeper is being used. It's too weak to bother
more distant clocks, and even the clock in the room isn't disturbed
during the dry-cleaning process. Well, installing a noise filter
inside the motor housing will stop the noise in a jiffy."
"Only one thing bothers me," Carl said slowly. "Why did more
clocks get out of synch when it rained?"
"That's easy," Jerry broke in. "When it rained, the kids
tracked in more mud, making it necessary to scrub more rooms
that night. So more clocks were off the next morning."
"I don't know how to thank you fellows," Mr. Stoner said
"Well," Carl suggested slyly, "you could say you needed us
to help you install that noise filter during the Latin period.
We're due to have a quiz, and -"
"Say no more!" Mr. Stoner interrupted with a chuckle. "I'm
sure I need you more than Caesar does today."
Carl & Jerry: Their Complete Adventures is now available. "From
1954 through 1964, Popular Electronics published 119 adventures of Carl Anderson and Jerry Bishop, two teen boys with
a passion for electronics and a knack for getting into and out of trouble with haywire lashups built
in Jerry's basement. Better still, the boys explained how it all worked, and in doing so, launched countless
young people into careers in science and technology. Now, for the first time ever, the full run of Carl
and Jerry yarns by John T. Frye are available again, in five authorized anthologies that include the
full text and all illustrations."
Carl & Jerry Episodes on RF Cafe
- Electronic Eraser,
- Electronic Trap, March
- Geniuses at Work, June
- Eeeeelectricity!, November
- Anchors Aweigh, July
- Bosco Has His Day,
- The Hand of Selene,
- Feedback, May 1956
- Abetting or Not?, October
- Electronic Beach
Buggy, September 1956
- Extra Sensory
Perception, December 1956
- Trapped in a Chimney,
- Command Performance,
Education, July 1963
- Treachery of Judas, July
- The Sucker, May 1963
- Stereotaped New
Year, January 1963
- The Snow Machine, December
Education, July 1963
- Slow Motion for
Quick Action, April 1963
- Sonar Sleuthing, August
- TV Antennas, August 1955
- Succoring a Soroban,
- "All's Fair --", September
- Operation Worm Warming,
Stomping, March 1962
- The Blubber Banisher,
- The Sparkling Light, May
- Pure Research Rewarded,
- A Hot Idea, March 1960
- The Hot Dog Case, December
- A New Company is Launched,
- Under the Mistletoe,
- Electronic Eraser,
- "BBI", May 1959
- Ultrasonic Sound Waves,
- The River Sniffer, July
- Ham Radio, April 1955
- El Torero Electronico,
- Wired Wireless, January
- Electronic Shadow,
- Elementary Induction,
- He Went That-a-Way,
- Electronic Detective,
- Aiding an Instinct,
- Two Detectors, February
- Tussle with a Tachometer,
- Therry and the Pirates,
- The Crazy Clock Caper,
Posted November 4, 2014