Mac's Radio Service Shop:
Barney Has a Birthday
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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
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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