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Mac's Radio Service Shop: Unusual New Equipment
June 1955 Radio & Television News

June 1955 Radio & TV News
June 1955 Radio & Television News Cover - RF Cafe[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.

John T. Frye's monthly "Mac's Radio Service Shop" techno-drama, written in story form - was usually an incognito lesson on circuit functionality or troubleshooting, how to deal with customers, industry regulations and news, or an introduction to new components and equipment. As the "Unusual New Equipment" title suggests, this time Mac described a few new items added to the service shop to aid in their work. Often when reading one of the episodes, I do a Google search on specific components or equipment mentioned in the article. He describes a special-purpose CRT (Sylvania's new 5AXP4 Television Receiver Check Tube) that could be used universally for troubleshooting in place of a wide variety of installed picture tubes. I've seem them on eBay for $30-$50. There is not much you cannot find on eBay if you watch long enough. He also bought a pair of 7x35 binoculars for inspecting TV antennas from the ground, and points out how a magnification greater than around 7x results in difficulty in holding them steady enough to be useful. My Celestron 15x70 SkyMaster binocs require a tripod or being steadied against a tree or house to keep the image steady. Stars are a constant streak when holding normally - especially after a day of drinking coffee.

Unusual New Equipment

Mac's Radio Service Shop: Unusual New Equipment - RF CafeBy John T. Frye

Barney was a little late to work, and he was hurrying, so he almost knocked down the customer emerging from the service shop carrying a tape recorder in his hand. However, with the quick reflexes of youth, he not only managed to avert the near collision but transformed it into a flourishing gesture of holding open the door. As he hurried into the service department of the radio and TV repair shop he found Mac, his boss, busily engaged in applying a coating of high-voltage shellac, or "corona gunk" as it was familiarly known, to the secondary coil of a horizontal deflection transformer that had developed a "blowout" at a point where a primary lead had sagged against the winding.

"There," Mac said as he put the combination cork-and-application-brush back into the bottle, "when it dries, that ought to hold the arc. That's the third coating I've put on, and each layer is supposed to provide about 10,000 volts worth of insulation. Unless the winding itself has been damaged, we've probably saved the owner the cost of a new transformer. Don't turn this set on, though, until that dope has thoroughly dried. It'll catch fire when it's wet."

Barney was not paying too much attention. Instead he was eyeing three intriguing-looking boxes the parcel post man had left lying on the bench. "What's in these?" he demanded.

"Three pieces of rather out-of-the-ordinary service equipment," Mac said as he began opening the smallest package. "You know I've always maintained a service technician ought to snoop around a bit in other fields now and then to see if he can't find equipment there that will make his own job easier. What you see here is the result of taking some of my own advice. First, there is this little transistor receiver that measures only five inches by three inches by an inch and a quarter. It's the very first practical transistor radio to hit the market, and it's a true superhet, with two i.f. stages, a.v.c. ferrite core antenna, and earphone jack for a hearing-aid type earphone accessory. I think it can be very useful to us in service work."


"I'll show you just as soon as I insert this 22½-volt hearing aid battery that powers it," Mac said as he snapped the back of the case on the little set and turned it on. Instantly the shop was filled with a surprising amount of volume. "Watch now," Mac said as he turned the receiver slowly about with his hand. At two points, one hundred and eighty degrees apart, the volume of the reception fell off sharply.

"When I was playing with one of these at the store, I noticed the null positions of the receiving loop were very sharp and positive. That gave me the idea we can take the little set up on roofs with us and use this directional characteristic to aim TV antennas. Every city with a TV transmitter around here also has one or more radio stations that can be easily picked up on this sensitive little job. As far away as we are, the radio tower and the TV antenna in each of these towns can be considered as being in the same direction from us for all practical purposes. S-o-o-o, all we have to do is find out where the little receiver says the radio station is and then point the TV at that point of 'the compass, and we'll have it right on the nose. What's more, this little set will be a jim-dandy to tuck in your shirt pocket when you are going out on a noisy reception complaint. You can tell at once if the noise is in the set or not. And I anticipate that in many cases this tiny little portable will lead us right to the source of the noise."

"You know what I think?" Barney asked as he watched Mac fondling the plastic case of the little set.

"No, and I'm not sure I want to find out," Mac replied cautiously.

"I think you're just trying to hatch up some good reasons so you can buy that little set and charge it up to the shop."

"Could be!" Mac said with a guilty grin. "I never could resist as neatly an engineered piece of electronic gear as this is; and when you consider it is the first practical transistor receiver well, you know I still have the first crystal receiver I built and my old Radiola !"

"Okay," Barney said with an understanding smile. "I don't blame you a bit. What's in those other packages?"

"Here's a pair of prism binoculars," Mac said as he removed them from their leather case. "They are made in the American zone of Germany; and while they are quite reasonable in price, they have a lot of good features. They are seven power and have 35 mm. objectives. All air-to-glass optical surfaces are coated with magnesium fluoride for better light transmission and to cut down reflections. Central focusing is used with provision for separate adjustment of the right-hand barrel. They have a hinged bridge and weigh only 16½ ounces and the field of view is 405 feet at 1000 yards."

As he chanted off these features, Mac walked to the front of the store and gazed through the binoculars at the rooftops across the street.

"Hey, let me look," Barney said as he tugged at Mac's elbow.

Obediently Mac surrendered the glasses, and Barney peered through them.

"Holy cow!" he exclaimed as he lowered the binoculars and then glanced through them again. "These things are powerful. Those TV antennas look like they're standing right outside the window. I can see every bolt, wing-nut, and rivet in them. These things surely show up my coffee nerves, though. It's hard to hold them still."

"That's why I didn't buy higher powered ones," Mac explained. "Seven power glasses are about as strong as can be satisfactorily hand held. At that, they make anything seem seven times closer than it really is. Few towers around here exceed seventy feet; so that means we can bring the antenna down to ten feet with the glasses. My thought is that these glasses will save a lot of leg work in climbing around on roofs and towers to inspect antennas and lead-ins. By watching the antenna while it is turned with the motor, we can spot troubles such as broken lead-lines, irregular motor action, loose elements or stacking bars, broken insulators and other such defects without ever stepping off the ground."

"Speaking of stacking," Barney offered with a faraway look in his eyes, "How's about my borrowing those binoculars to take with me to Ideal Beach some Sunday? Some of the babes you see over there are really stacked, and -"

"Never mind!" Mac hastily interrupted. "You can get into enough trouble with just your bulging baby blue eyes."

"There's still that biggest package," Barney reminded.  

Mac opened the end of the cardboard carton that folded out to form a carrying handle and lifted out a small round picture tube.

"Is that a scope tube?" Barney wanted to know. "It's shaped more like a picture tube, but surely we haven't got any sets in the store with that small a screen."

"This tube," Mac said with a quizzical grin, "is designed to replace magnetically-deflected picture tubes up to twenty-four inches or so."

"Oh yeah; then it must be made of rubber," was Barney's dubious comment.

Sylvania's 5AXP4 Television Receiver Check Tube (eBay) - RF Cafe"No, it's Sylvania's new 5AXP4 Television Receiver Check Tube that was described in the February, 1955, 'Sylvania News.' It is intended to replace almost any picture tube you are likely to find in a modern black-and-white TV receiver-but only for testing purposes, of course. It will take anode voltages up to 18,000 volts, requires no ion trap, and is self-focusing. You know I've long wished we could use the fast, reliable, conclusive tube-substitution method of checking' the picture tube that is so useful in checking the other tubes in a TV set. Now, thanks to this little job, we can."

"How do you use the tube?"

"Just slip the receiver's yoke over the neck of the tube, put the picture tube socket on its base, and connect up the high-voltage lead. The manufacturer suggests using one of those centering-magnet assemblies with the magnets removed to hold the tube in position in the yoke. This assembly clamps the neck of the tube between flat springs so that it will stay in position."

"That will be pretty handy," Barney said with mounting enthusiasm. "It means we can leave the picture tube right in the cabinet in most cases when we are sure there is nothing wrong with the tube itself and bring only the chassis and deflection yoke to the store. That will be a real help. I never did relish the idea: of lugging those big tubes around. There's too much danger of breaking them. On top of that, they're heavy and hard to get out."

"Don't overlook the sales appeal of this little service tool," Mac said as he used his pocket steel tape to prove the tube face was only five inches in diameter and the over-all length was but ten and a half inches. "When we can show our customer that his set can put out a bright sharp picture on this tube while the picture he gets on his own is weak and faded, if he gets any picture at all, his sales resistance will evaporate. This little persuader will present a much more graphic and convincing argument in favor of ordering a new tube than will a mere meter reading on a tube tester.

"I think this test tube will be especially appreciated by small shops such as we are," Mac went on. "We can't carry a large inventory of picture tubes; so usually we do not have a good tube to try in one of those hard-to-be-sure cases where you feel reasonably confident the picture tube is at fault but you want to be dead-certain before telling the customer a new tube will cure his trouble. This 5AXP4 will take care of those cases for us."

"Changing the subject for a moment," Barney said, "didn't I see Jim taking his recorder out with him? What was wrong? That about had you stumped yesterday."

Mac smiled broadly as he replied:

"Yes, that was Jim, and the mystery is solved. What puzzled me, you'll remember, is how the recorder could possibly do what he reported it was doing: namely, suddenly go berserk during, playback and erase recorded material while it was playing it and leave only a wavering audio note in its place. He said a recording might sound fine the first two or three times he played it, but the next time he wanted to listen, only this note could be heard -and that was all I could hear when I put one of his tapes on our recorder, too.

"Jim's hobby is recording circus bands - he used to be with a circus, you know - and several of his prized and irreplaceable recordings were ruined by this strange fault of his recorder. What made the thing worse was that I could not make it happen here in the shop. I made a test recording and played it over and over without anything unusual occurring. Finally, while lying in bed last night, I got an idea of what might be happening; and the first thing this morning I tried it out. Sure enough, I could make the same thing happen to the test recording that had been happening to Jim's calliope music."  

"What was wrong?" Barney demanded impatiently.

"You'll remember his recorder has two control knobs. One has Play-Off-Record positions; the other reads Wind-Off-Rewind. A red button must be pushed down before the first knob can be turned to Record, and it is held depressed as long as this knob stays in the record position but snaps back up when the knob is turned to Off. Neither knob can be turned from the Off position unless the other knob is already in that position. However, the red button can be held down manually while the Rewind-Wind knob is worked.

"That's what I did. I simply held this red button down while I was rewinding the tape. This activated the record and erase heads and wiped the recording from the tape. At the same time the signal from the bias oscillator was put on the tape. Remember that the tape was travelling at about ten times its ordinary speed. As you know, slowing down the speed of the tape below the speed at which it was moving when a recording was being made has the effect of lowering the pitch of the recorded material. In this case, when the tape was played at normal speed, the supersonic erase signal that was recorded during fast rewind was brought down into the audible range and provided that mysterious wavering note we heard."

"What was Jim doing wrong?" "Since he only used the recorder once or twice a year, he forgot how to operate it from one time to the next. He remembered, though, that the red button had to be depressed under some circumstances; so he just depressed it every time he moved any of the knobs. During rewind he held the button down so that he would not hear the normal monkey-chatter you get when the tape is moving fast and the speaker is not cut out or the volume turned down. Sometimes he pushed it far enough to engage the recording switch; other times he did not. I simply had him show me how he operated the recorder before I told him what I had found out; and sure enough, that is what he was doing. I've got him all squared away now, arid he says he will see I get a couple of passes the next time the circus hits town. If a certain obstreperous redhead that I know doesn't consider such entertainment beneath his dignity, I'd be glad to include him in this bucolic whingding upon request."

"It's a date!" Barney exclaimed. "I'll buy the peanuts."



Posted May 9, 2024
(updated from original post on 2/15/2017)

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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