February 1966 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
OK, I'm embarrassed once
again. In this 1969 issue of Electronics World magazine, a device called
is mentioned the Mac's Service Shop episode entitled, "Keeping up with New Components."
It was a totally new word to me. According to Wikipedia a thyrector is a type of
voltage suppression (TVS) diode, aka a "transil" (another unfamiliar term).
Maybe I have heard of both of them, but if so, I don't remember. You might think
with all the vintage electronics magazine I have read, along with having been in
the field since the 1970's, this wouldn't have caught me by surprise. Interestingly,
the title of the article does not mention that it is a Mac's Service Shop story,
but it is. Anyway, enjoy the story.
Mac's Service Shop: Mac's Service Shop: Keeping Up with New Components
by John T. Frye
Business at Mac's Service Shop was becalmed in the February doldrums. Pocketbooks
were still suffering from the Christmas trauma, and taxpaying time had begun to
loom darkly on the horizon; so customers were having only essential service work
done. Mac and Barney had cleaned and re-arranged the entire shop; they had checked
and recalibrated all their test equipment; but now they were entirely caught up.
Mac sat on a stool, chin in hand, trying to think how he could keep his restless
red-headed assistant gainfully employed - or just employed.
Suddenly he slid off the stool and took three bright-red display cards from a
cabinet and placed them, together with a thick, paper-bound manual, on the bench
in front of Barney.
"What are those nasty-looking things?" the latter asked, peering suspiciously
at the various small components contained in formed pockets of the clear plastic
covers of the cards.
"They are Experimenter's Kits put out by RCA last fall.
That large card contains five diode rectifiers, an n-p-n silicon transistor,
a p-n-p germanium transistor, and a heat-sink-mounted silicon controlled rectifier.
As explained in the manual, these constitute the major items used in the construction
of the basic universal motor-speed control and lamp-dimmer unit. The other two cards
contain add-on kits to be used with the basic unit. A photocell in the light-sensor
kit permits conversion of the basic unit into a light-activated switch. Three thermistors
of different ranges and special solder for mounting them contained in the heat-sensor
kit allow changes in temperature to control devices plugged into the basic unit.
"The manual explains in great detail how fourteen
different control devices can be built from these three kits, but it does much more
than that. It goes into the theory of diodes, transistors, and silicon controlled
rectifiers in a thorough manner; it describes simple circuitry for testing every
component furnished with the kit and for testing sub-assemblies of the basic unit;
and it shows normal scope traces to be found at various points in the silicon controlled
rectifier circuit with various levels of the controlling signal. The construction
of a two-transistor regenerative 'triggered switch' is given and the action explained.
I particularly like the manual because the actual construction information is simple
and yet detailed enough so that almost anyone can build and use the devices; nevertheless,
the theory of operation is not 'watered down' below the technician level. When you
finish constructing, testing, and understanding the devices described, you'll know
a lot more about the practical use of silicon controlled rectifiers, photocells,
and thermistors than you do now."
"You mean you intend for me to build up these gadgets?" "Right. Most of them
can be put to good use right here in the shop. The motor-speed control will work
fine with our electric drills. The light dimmer, light-activated switch, and electronic
flasher can all be used to create crowd-stopping displays in the front window. The
electronic overload switch is just the ticket to monitor power drawn by a cooking
intermittent TV set and to cut it off when something fails and the power consumption
rises above the normal level. And one of the thermistors can be placed in a critical
cabinet area or fastened directly to a component so that the set will be automatically
switched off if the temperature rises above a preset value. But you don't need to
limit yourself to the devices described in the RCA manual," Mac concluded, taking
another manual from the cabinet and handing it to Barney.
"Gee, how lucky can a guy be?" Barney asked sarcastically. "That's the 'Silicon
Controlled Rectifier Hobby Manual' put out by G-E," Mac explained, ignoring Barney's
sarcasm. "It contains construction information on several other interesting SCR
devices you can build and tryout during your spare time here in the shop. I'll be
especially interested in seeing you check out various suggestions in the manual
for getting rid of radio interference created by the abrupt turning on of the controlled
rectifier during each cycle or half-cycle. Also, you will find that thyrectors are
used across the line to suppress transients that might damage the rectifiers, that
light-activated switches are described, and that unijunction transistors are used.
Experimenting with the apparatus described will give us an opportunity to observe
the behavior of all three devices. And some of the equipment in this manual employs
zener diodes. While we both know how zener diodes work and encounter them more and
more frequently in the transistorized equipment we service, it won't hurt either
of us to play around with them in experimental equipment where we can observe and
measure their voltage-limiting action under deliberately induced extreme conditions."
"I think I'm beginning to see what you're driving at," Barney mused. "You're
not primarily interested in using the devices you want me to build. What you really
want is for me to obtain some first-hand experimental knowledge of various types
of semiconductors and related members of the 'istor' family that will be of use
to me in the servicing of home and industrial equipment."
"Precisely!" Mac applauded. "We both know there's a big difference between learning
about a new component from reading about it and from actually working with it. Back
in the early days of servicing a technician was invariably an experimenter, too.
When he wasn't working on a customer's receiver, he was building his own and trying
to improve its performance. Every time a new tube or a new circuit or a design for
a new antenna came out, he was quick to try it out; and a great deal of what he
learned from this experimenting was of great practical value to him in his service
"But nowadays things are different. Very few present-day service technicians
do any experimenting or any construction worthy of the name. We excuse ourselves
by saying we're too busy to 'fool around' with new components and that we can learn
all we need to know about them when we encounter them in new equipment. That's a
little like a doctor's claiming he can learn all he needs to know about new diseases
by treating them in patients. who bring these diseases to him. He can learn, all
right, but it's likely to be rough on the patient and very time-consuming.
"Just as a doctor learns about the human body thoroughly by dissection and keeps
himself abreast of new techniques by sitting in on new operations, so the technician
should keep himself thoroughly informed on the capabilities, weaknesses, and peculiarities
of new electronic components used in equipment he intends to service by experimenting
with these new components as soon as they are made available at reasonable prices
- before they are incorporated into new electronic equipment for home and industry.
"Many manufacturers are aware of this, and they are doing what they can to help
the technician by bringing out kits and manuals such as those on the bench. Leaflets
describing the parameters of new semiconductor devices and showing possible applications
of these devices can be obtained free of charge from practically any manufacturer
as soon as the devices are introduced. The technician who obtains a leaflet and
one of the devices and experiments with it will be in a position to approach a piece
of equipment using one of the devices with complete confidence. He knows what it
is supposed to do, and he is familiar with any peculiarities or weaknesses it may
have. He will be prepared to decide quickly whether a defect in that particular
component is causing the trouble with the equipment or not."
"You're making sense," Barney admitted. "I know for a fact that when I'm working
on a piece of equipment containing an unfamiliar component, I'm always haunted by
the possibility the trouble may lie in that little puzzler I'm not prepared to test."
"I know what you mean. And we have to face up to the fact that more and more
of these exotic devices are being used in ordinary home and factory equipment every
day," Mac continued. "Controlled rectifiers have become cheap enough to be built
into many drills, mixers, jig-saws, movie projectors, lamps, etc., and 1 think we've
just scratched the surface of the possible uses for this versatile semiconductor.
Our audio oscillator uses a thermistor in series with a capacitor across the load
resistor of one of the amplifiers to hold the output nearly constant regardless
of the frequency. And you know how often thermistors are used in liquid-level controls
and temperature-monitoring devices in industry. Voltage-variable capacitors are
used to vary the b.f.o. of communications receivers and to provide delta tuning
of the receiver circuits of several ham and CB transceivers. They are also used
to provide frequency sweeping of signal generators and in a.f.c. circuits. Photocells
are almost as common as flashlight bulbs. They do everything from opening huge garage
doors to adjusting the iris opening of even small and inexpensive cameras for the
"You needn't beat the subject to death. 1 get the picture," Barney interrupted.
"You furnish the jazzy electronic components and the spec sheets, and I'll certainly
whip them up into circuits and put them through their paces. I really enjoy building
and experimenting. What's more, I'll even let you look over my shoulder while I'm
doing it so that I won't be the only hep guy in the shop. But now, if you don't
mind, I'd like to get started putting this motor control and lamp dimmer together.
Mac nodded agreement, and Barney, humming "Getting to Know You" slightly off-key,
started to work.
Posted August 24, 2022
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive technodrama™ stories was the brainchild of none other than John T.
Frye, creator of the Carl and Jerry series that ran in
Popular Electronics for many years. "Mac's Radio Service Shop" began life
in April 1948 in Radio News
magazine (which later became Radio & Television News, then
World), and changed its name to simply "Mac's Service Shop" until the final
episode was published in a 1977
Popular Electronics magazine. "Mac" is electronics repair shop owner Mac
McGregor, and Barney Jameson his his eager, if not somewhat naive, technician assistant.
"Lessons" are taught in story format with dialogs between Mac and Barney.