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June 1948 Radio News
 [Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Radio & Television News, published 1919-1959. All copyrights hereby
acknowledged.
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I always look forward to another
of John Frye's "Mac's Radio Service Shop" techno dramas. They are always an entertaining
mix of interaction between Mac and his sidekick technician Barney, and a meaningful
lesson on troubleshooting circuits, dealing with customers, or interpreting electronics
industry news. Often it is a combination thereof. This installment entitled "Barney
Has a Birthday" appeared in the June 1948 issue of Radio News magazine;
it was one of the earlier stories. In fact, it is now that Barney is promoted from
a mere shop hand to a fledgling electronics technician. Mac has been preparing him
for the duty with mentoring and assigning reading material. Mind you Barney is no
rank amateur at electronics because, in fact, he is a full-fledged radio amateur
- a Ham operator in other words (notice the clever juxtaposing of terms here). Having previously
cobbled together a radio kit or two is not adequate preparation for servicing electronic
appliances of paying customers of course, but at least it demonstrates aptitude
and a genuine interest in learning.
Mac's Radio Service Shop: Barney Has a Birthday
 By John T. Frye
Miss Perkins, precisely at two minutes to nine, stepped inside Mac's Radio Service
Shop ready to start another day as its very efficient office force. Before the door
could close behind her she was pounced upon by a red-headed demon and swung dizzily
about the office while the demon sang very lustily and slightly off-key, "Oh, waltz
me around again, Matilda!"
"Barney Jameson, you let me go!" she gasped. "Let me down this instant!"
After one last wild swing, Barney obediently deposited her on her desk, her hat
tilted rakishly over one eye, and her horn-rimmed spectacles far down on her sharp
little nose.
"What on earth is the matter with you?" she demanded, her hands fluttering about
trying to repair the damage.
"It's my birthday, Matilda - I mean, Miss Perkins," Barney explained with such
a dazzling smile that she could not resist smiling back just a little.
"And that, when you remember that our assistant is a wild young Irishman, should
explain everything," Mac said with a chuckle from where he had been watching in
the open door of the service department. "Well, my young bucko, you come on back
here. I have a birthday present for you."
Winking and leering wickedly over his shoulder at Miss Perkins, Barney made a
dash and slid through the door into the service department.
"Where it is? Where's the present?" he demanded.
"Right there," Mac replied, waving at the service bench. "Starting today, you
are going to do some trouble-shooting."
"Honest, Boss ?" Barney asked happily. "You mean you are really going to let
me show you how much I have learned out of those books I've been beating my brains
out on?"
"How much or how little," Mac said dryly. "First, though, I want to brief you
a little on procedure. To begin with, there is the matter of testing tubes. The
roller chart on the checker shows you how to set each control for a particular tube.
Always set up the controls and then double-check the settings before you stick a
tube in the tester."
"That's to keep from burning out a filament, I presume," Barney said airily.
"You presume right, and another thing toward the same end is to arrange the tubes
to be checked in this tray so that those with the lowest filament voltages are on
the left and the filament voltages are progressively higher as you go toward the
right. For instance, you might have a couple of 6SS7's, a 12SA7, a 12SQ7, a 35Z5
and a 50L6 laid out in that order. If you checked from left to right, you would
run no danger of putting a tube in the tester with too high a filament-voltage setting,
for every change necessary in this control is toward a higher setting."
"Check and double-check," Barney said, making a circle out of his thumb and forefinger.
"Don't forget to adjust the line voltage on the checker, either," Mac admonished.
"Do it with a tube plugged in."
"Do I have to check the line-voltage for each tube?"
"Ordinarily, no. Adjust it with the first tube in the checker and let it alone
for the rest; however, when testing a tube with a heavy filament current, such as
an 83, you may have to boost it up a little."
"I've got it," Barney stated. "If the hand goes into the green, I stick the tube
back in the set; if it stays in the red, I throw the tube away; and if it stops
in that little orange space, I toss a coin to see whether I throw the tube away
or use it."
"It's not quite that simple," Mac said with a grin. "In the first place, you
check all the elements for shorts by throwing these switches and watching the neon
lamp. While making this test, you keep tapping the tube with this little rubber
hammer; and don't let me catch you hitting it as though you were trying to drive
a tent-stake," he warned, trying to scowl fiercely.
"Okay, Boss, okay!" Barney replied, holding his arms up as though warding off
an expected blow. "I'll see you don't catch me."
"Don't just strike the tubes on top. Tap them first on one side and then on the
other," Mac went on. "Don't neglect to check each section of multi-purpose tubes
separately."
"What do I do with those that read 'doubtful'?" Barney asked.
"I usually leave that up to the customer. Of course, if a new tube makes a noticeable
difference, I replace the old one; but often this is not the case. Usually, though,
the customer will tell you to discard the doubtful ones."
"And now let's talk about the service bench," Mac went on. "For the present,
you will not use the scope, the signal tracer, or the vacuum-tube voltmeter. Those
belong in the high school of radio servicing, and you are still in the grades. The
signal generator and the multimeter there are your trouble-shooting weapons, and
they are cap· able of telling you a lot more about what is wrong with a radio than
you will be able to understand."
"Such cruel, cutting words - and on my birthday, too!" Barney muttered darkly.
"You will hear a lot worse words if you damage that meter," Mac warned. "Take
a good long look at it. Notice how straight that pointer is. See how snugly it hugs
zero. Watch how smoothly it swings. Mind that it stays that way."
"Do you have any helpful suggestions - as though I didn't know," Barney said
sweetly.
"Plenty of 'em. For one thing, while checking receiver voltages in general, stay
on the five-hundred-volt range. With that big scale, you can easily read it down
to five volts. Most receiver voltages will not go much beyond half-scale, and if
you happen to get the polarity reversed - and this should not happen often if you
watch what you are doing - you are not likely to bend the pointer."
"Another precaution," Mac continued, "is always to pull the receiver plug before
you go probing around with the ohmmeter; and it is also a good idea to check first
with the voltmeter before using the ohmmeter if the set has just been turned off.
Quite often an open speaker field winding or bleeder resistor will allow the filter
condensers to remain fully charged even though the line plug has been pulled for
several seconds. To put the ohmmeter across a fully charged filter condenser will
damage the instrument as quickly as placing it across the same points with the set
turned on."
"Why do you always plug sets you are working on into one of those three outlets
marked 'Receiver Test?' " Barney inquired.
"Because those three sockets are fed from the line through an isolation transformer
with a tapped secondary. The tap-switch just below that 150 volt a.c. meter allows
me to put any voltage from 90 to 130 volts on those out-lets. That is a great help
in cracking some kinds of intermittents."
"Why do you call that an isolation transformer ?"
"Because that is its main job. It isolates the receiver fed by its secondary
from the line-voltage circuit that has one side grounded. Lots of a.c.-d.c. sets
have one side of the line attached directly to the chassis, and quite often you
will find a transformer set in which the bypass condenser from one side of the line
to the chassis has been shorted out by lightning. If you had one of these sets plugged
directly into the light circuit, and if the hot side happened to be the one going
to the chassis, and if you touched the chassis with one hand and any grounded object
with the other -"
Barney rolled his eyes toward the ceiling and pretended to be plucking an imaginary
harp to show he understood. For once, though, Mac did not smile at his clowning.
"Barney," he said seriously, "I do not expect you to remember everything I tell
you, but here is one thing I want you never to forget: Never underestimate the danger
that lurks in any electrical circuit. Working with radios every day, as you soon
will be, it is all too easy to fall into a 'Who's afraid?' attitude toward the shocks
you can get from a receiver. Just try to remember that there are hundreds of people
lying out in the cemetery looking at the wrong side of the grass who were put there
by the 110-volt a.c. house current. It only takes from seventy to ninety milliamperes
of current to cause death. Under the right conditions, sixty volts or less can drive
that much current through your body. Many of the sets you will be working on will
have upward of seven hundred volts across the power transformer secondary, and any
of them can furnish more than a hundred milliamperes of current."
"Yet," Mac continued, "you will hear some chowder-heads in the service game boasting
about how often they are 'bitten' with electricity every day. They seem to think
it is to their credit. If they had any sense, they would know that the good mechanic
is always the careful mechanic."
Barney, too, looked sober as he promised, "I'll remember that, Mac."
Posted January 10, 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
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.
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