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June 1968 Electronics World
 Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
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The debate about upgrading
electronics service shop equipment from vacuum tube to solid-state instruments
was raging in the late 1960s, when this Mac's Service Shop story appeared in
Electronics World magazine. Barney is querying Mac regarding FET-based VOM
performance specifications he is considering to replace a VTVM. He covets the
Hewlett-Packard 217A square-wave generator, delivering clean 1 Hz-10 MHz waves
with 5-ns rise time and scope triggering, justifying its $300-$400 cost for
precise scope testing. An electronic counter for 5 Hz-10 MHz frequencies, with
four- or six-digit readouts and line- or crystal-gated accuracy, tempts at
$350-$700. Barney wants a $125 Model 1110 secondary standard for WWV-calibrated
precision. Benefits of solid-state include compactness, portability, ruggedness,
and reliability over tube gear, though repair challenges from ICs, obsolescence,
and parts scarcity loomed. Ultimately, they resolved to embrace progress while
fixing sets with old tools as prudence dictated.
Mac's Service Shop: Solid-State Service Instruments
 By John T. Frye
"Hey Boss," Barney said to Mac, his employer, you've been mooning over that catalogue
for a good half hour. Sure and I know your name's McGregor, but is the prospect
of having to turn loose of a few bucks all that painful to a Scotsman ?"
"Keep a civil tongue in your head, you Black Irishman!" Mac retorted with a fierce
scowl. "It's not giving up the money that hurts; it's just that we canny Scots like
to do the best we can. I want to order some new service equipment, and I find there
are a lot of ways to go. Solid-state devices have invaded the service instrument
field, just as they have clone in almost every other electronics field; and this
has sort of muddied the water. I used to know the specs of most popular service
instruments by heart, but now I find it's a whole new horse race - if you don't
mind my mixing a few metaphors!"
"I don't mind; I'm used to it; but what kind of instruments are you thinking
of buying?"
"Well, for one thing, we need a new v.t.v.m., or equivalent, for use in making
outside calls. I'm wondering if one of those new solid-state v.o.m.'s might not
be a better buy. Thanks to the use of FET's, such a v.o.m. achieves an input resistance
at least as high as the 11-megohm input of a conventional v.t.v.m. One of those
I've been looking at has a built-in power supply for working off the line or it
can be switched to self-contained batteries. That would make it handy for working
on equipment where there's no convenient a.c. outlet for plugging in the instrument;
yet we could conserve the batteries when this feature isn't needed."
"How about accuracy?"
"It is rated just as good as the tube-type instruments. In fact, I should imagine
the long-time accuracy might be better because you wouldn't have the tube-aging
factor to contend with. Also, since other components of the instrument will not
be subjected to self-generated heat, as they are in a v.t.v.m., these components
should last longer. All in all, I shouldn't be at all surprised if this new type
of v.o.m. night not eventually put the v.t.v.m., that faithful old work horse of
the service technician, out to pasture."
"Kind of sad, ain't it ?" Barney mused. "But I guess that's progress. What other
goodies are you contemplating buying?"
"I'd like to have a really good square-wave generator that will have a fast enough
rise time to let us take full advantage of the capabilities of our new wide-band,
driven-sweep scope. I want something that will produce a good clean square wave
up to at least 1 MHz. The Hewlett-Packard Model 217A I've been looking at is typical
of a new breed of fully transistorized generators that will easily satisfy such
demands. In fact, it will produce square waves from 1 Hz to 10 MHz with a rise time
of 5 nanoseconds or better. The 'on' time of the square wave - or the relative length
of the 'bottom' horizontal portion of the square wave compared with the 'top' horizontal
portion - can be varied between 25% and 75 %. A triggering source for the scope's
driven sweep is also provided.
"The $300-$400 price tags on these instruments sound salty when compared with
the cost of the usual service -type square-wave generator whose rise time is measured
in microseconds or even milliseconds, but the price is still a lot lower than it
was before fast-acting solid-state switching devices got into the picture.
"If we're willing to settle for a rise time of ten nanoseconds and dispense with
some of the other features, we can get the price down below $200; but I'm inclined
to go whole-hog and get the better instrument. Admittedly, that rise time is better
than we need with our present scope; but in square-wave testing, if you have to
make allowance for the limitations of the scope amplifier and for the limitations
of your generator, you end up feeling quite unsure about what you are really seeing
on the tube face. How much of the distortion seen there is produced by the amplifier
or device being tested, and how much is produced by your equipment? It seems to
me the logical place to start upgrading is with the signal source. If you can be
certain your generator is producing a clean, fast -rise square wave at a repetition
rate in the MHz, you are in a position to evaluate the contribution the scope amplifier
makes to the distortion seen. Knowing this, you can then proceed to check the amplifier
or delay line with confidence."
"Sounds logical," Barney agreed. "Does that wind up your buying spree, Diamond
Jim ?"
"Not quite. For a long, long time I've wanted an electronic counter to measure
frequency, and it looks as though the use of transistors and integrated circuits
may eventually enable me to satisfy my wish. In fact, I can buy one right now that
will count from 5 Hz to 10 MHz for only $350 if I am willing to accept a four-figure
readout and a gate based on the power-line frequency. This basic model has gate
periods of 1 second and 0.1 second. For $125 more, you get a six-figure readout,
which, of course, would be much better for high-frequency measurement."
"How about the accuracy? Doesn't that gate's being keyed to the line frequency
impair the accuracy a great deal ?"
"Depends on what you mean by 'a great deal'. The accuracy of the count is the
usual plus-or-minus one Hz plus- or-minus the accuracy of the line frequency. In
the United States, this accuracy is typically better than 0.1% for commercial power.
But if you need greater accuracy, you can get it for about double the money in a
counter whose gate is operated by a stable 1-MHz crystal oscillator. This model
has gate periods of .01, 0.1, 1, and 10 seconds with a five-figure readout. A six-figure
readout is an option. And, of course the counter can be used to measure time intervals
from 1 microsecond to 1 second.
"The point I want to stress is that these and similar counters coming on the
market from the development labs make extensive use of IC's. This leads to a reduction
in size and cost and an improvement in reliability." "Hey, do I get to say anything
in this dialogue, or do I have to content myself with being your straight man ?"
Barney demanded. "If you really have anything to contribute - which I doubt - I
might be persuaded to listen," Mac answered.
"Thanks a great big heap!" Barney retorted. "I was just going to mention that
International Crystal has just come out with a Model 1110 transistorized secondary
frequency standard with outputs at 1 MHz, 100 kHz, and 10 kHz. Used in conjunction
with a general coverage communications receiver, this standard can be calibrated
against WWV to provide an accuracy of one part in 1011. The long-term
stability of the 1-MHz oscillator is claimed to be plus or minus 10 Hz over a range
of 40 °F to 100 °F. While this is not in the league with the counters you were discussing
and would require the use of an external receiver and some operating skill to read
frequencies accurately, it only costs $125 and would be plenty good enough for most
amateur radio or service technician measurements."
"That is interesting, and I'm going to look into it," Mac promised. "But in our
discussion we've just scratched the surface of solid-state applications to service
instruments. Digital voltmeters; transistorized scopes; signal, sweep, and marker
generators; dot and color bar generators - well, you just name it, and solid-state
versions are either on the market or are in R & D laboratories."
"I'm all for it," Barney offered. "For one thing, the use of transistors and
IC's produce instruments that are smaller, easier to carry, and that take up less
bench room. What's more, they are rugged and not easily damaged by jars or vibration.
These things are important in portable instruments you have to lug along on house
calls. Finally, from our own experience, we know solid-state devices fail much more
rarely than do tubes; so it would seem safe to assume these new instruments will
last longer and require less service."
"I agree with everything you say, but that last point brings up one disadvantage
of the new instruments: they are not going to be so easy to repair when something
floes go wrong with them. IC's are not readily tested %with the equipment and know-how
found in the average service shop. Furthermore, changing a critical IC or even a
transistor in a service instrument may make recalibration necessary.
"Another thing: there's not as much standardization and stability in the stocking
of transistors and IC's as there is in tube stocks. 13v the time one of these solid-state
devices hits the market it may be already obsolete because a new and improved type
is emerging from its own lab or the labs of competitors. We both know instrument
manufacturers stuck pretty close to well-established and popular tubes, avoiding
the new and the esoteric; so getting replacement tubes was never a problem. I can't
help wondering how true this will be of IC's and transistors. Will we be able to
get replacements in five or ten ears ?"
"You've got a point," Barney said; "but I still like transistorized service equipment.
Surely the instrument manufacturers will keep a goodly stock of replacement IC's
and transistors on hand - or at least the reputable manufacturers will."
"Okay, okay!" Mac said. "I'm not arguing with you. I just wanted to mention what
might be a couple of small drawbacks to transistorized service equipment. Like you,
I'm still for it because the advantages far outweigh the disadvantages. At any rate,
I'm resigned to having everything transistorized. Any day now I expect someone to
come out with a transistorized coat-hanger. But now suppose we get busy and see
if we can fix some TV sets with our out-of-date tube-type service equipment!"
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
Electronics
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. There
are 131 stories as of January 2026.
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