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Mac's Radio Service Shop: Cabinet Crisis
March 1955 Radio & Television News Article

March 1955 Radio & TV News
March 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.

Plastic is one of those materials that seems like it has been around since the dawn of time - like metal. There was an Iron Age in the 1,000 BC timeframe (depends on location), but the Plastic Age - not that there officially was one - did not begin in the commercial world until World War II. If you note in older photos and films, there was not much, if any, in the way of objects made of plastic before the 1940s. In fact, the formulation and production of some types of plastic like Plexiglas and polycarbonates was considered a matter of national security for a while both for Allied and Axis powers. Bomber and fighter aircraft windshields were made of the material. After the war, use of plastics for industrial and consumer products exploded due to the much easier manufacturing of product enclosures, knobs, and parts with complex shapes. Lighter weight, lower cost, easy application of color, and in some cases greater robustness made plastic very popular with consumers. Plastic does have its drawbacks compared to the wood, metal, and phenolic materials previously used for radios, TVs, and phonographs, and Barney experienced one of them in this episode of Mac's Radio Service Shop from a 1955 issue of Radio & Television News magazine.

Mac's Radio Service Shop: Cabinet Crisis

Mac's Radio Service Shop: Cabinet Crisis, March 1955 Radio & Televsion News - RF CafeBy John T. Frye

One of Barney's most consistent and attractive characteristics was his normal sunny disposition; so when Mac, his employer, stepped inside the service department after lunch and caught sight of Barney standing in the middle of the room with a most lugubrious and rueful look on his freckled countenance, it was quite a shock.

"Nothing could be as bad as you look," Mac hastened to say with conviction. "Pull in your lower lip before you step on it. What's wrong?"

Barney pointed wordlessly to an object on the bench. Looking closely, Mac saw it had been a small a.c.-d.c. radio with a red plastic cabinet; but now the top of the cabinet had softened and drooped down over the tubes and i.f. transformer cans so that they became so many formless bumps beneath the melted red sheet. The dial markings on the front of the cabinet were pulled and distorted in appearance like the face of one of the limp watches in a Dali painting.

"What did you do to that cabinet?" Mac demanded as his forehead creased in a frown.

"Now don't flip your lid," Barney aid hastily. "I've already called the distributor long-distance and ordered a new cabinet which should be in tomorrow. Naturally, I'll pay for both the call and the cabinet." "But how did you melt it down like that?" Mac persisted, a grin tugging at the corners of his mouth in spite of himself as he looked at Barney's woebegone expression.

"This set will not stay in alignment. You can set the i.f. trimmers right on the nose, but after the set plays for a few minutes they drift out of line. I decided to see if heat was causing the trouble by turning our infrared spot light on this i.f. transformer can right here on the back of the chassis. Since this would take only a minute, I didn't bother to take the chassis out of the cabinet. Just as I set up the lamp, a customer came in the front door. I went to see what he wanted without turning off the lamp because I thought I'd be back in a sec or so.

"Well, he was one of those characters who insist on giving you a complete case history of his cigar-box receiver before he entrusts it to your tender care. I had to listen to its age, its many original virtues - including unmatched tone - the horrible tortures it had endured at the hands of other unscrupulous and unprincipled service technicians, and finally its present symptoms in the most minute detail. He finished his long-winded discourse with a little apple-polishing comment on how highly our service had been recommended to him and how sure he was that we would do him a splendid job at a very reasonable price. He was especially emphatic about this "reasonable price" angle. To cut a long and painful story short, it took me a good quarter of an hour to hear him out; and when I suddenly remembered the heat lamp and dashed in here, I saw this gooey and disgusting mess."

"Well," Mac said slowly, "I guess it has taught you a lesson; so I suppose the store can absorb the cost of tuition. These new plastic cabinets require different handling than the Bakelite ones did. Remember that woman who brought in the kitchen receiver that had been melted down simply because she left it sitting on top of her stove too near the oven vent while she was baking? And there was that portable receiver case that practically ran into a puddle when it was parked too near the toaster on the breakfast table.

"Keep in mind these new cabinets are soft and have a high gloss that should be protected. Never turn one of them upside down or face down on a littered bench while you are removing the chassis screws. A sharp-cornered little piece of solder is all it takes to gouge a deep scratch in the soft surface. Always spread a clean, thick cloth down first. I've noticed in particular that you've got to be darned careful about using any cleaning fluid on these cabinets. Most of them are very allergic to either carbon tetrachloride or acetone. Wiping the surface of a cabinet with either of these will destroy the gloss and leave a sticky, lint-trapping smudge that can never be erased. It's a good rule never to use anything but mild soapy water to clean plastic cabinets of any sort. This may be a little slower, and you have to stir in more elbow grease, but it is much safer."

"I'm convinced the only foolproof procedure is to get the chassis out of the cabinet as quickly as possible and then to store the cabinet in a safe place while you work on the set," Barney said earnestly. "A mere dab with a hot solder gun tip will put a deep dent in one of these new jobs. I notice a lot of our customers do not want to go for the price of a new cabinet when the old one is cracked. They expect us to glue the crack together. Temporarily, you can do a pretty neat job by coating the broken edges with speaker cement and then pressing them together, but I notice that after a while the crack opens up, especially after the cement dries out. Is there any good way of preventing this?"

"I've had pretty good luck in gluing a thin strip of heavy cheesecloth along the crack inside the cabinet with a good wood adhesive," Mac offered. When the glue sets in the meshes of the cheesecloth, it produces a sort of unyielding patch bonded right to the cabinet that prevents the crack from spreading. At least cabinets are coming into the shop that I repaired in this way two and three years ago, and they are still OK."

"Hey, what have you got there?" Barney broke in as he noticed a half dozen flat little cardboard boxes in Mac's hand.

"These are Dubbings new D-210 'Plus-50' Music and Test Tape Samplers," Mac answered. "Each consists of a three-inch reel generously filled with about 275 feet of Reeves Mylar base 1-mil-thick tape that is advertised as being impervious to temperature and humidity and practically indestructible. The tape is recorded at 7 1/2 ips, full-track, with two timing beeps, a fifteen-second 5000 cycle tone, and about six and a half minutes of high-fidelity music recording, including Bizet's Carmen Overture and Rimsky-Korsakov's Song of India."

"What are you going to do with them? You've already got that Dubbings professional test tape that you're so fussy about."

"That's the point. I'm going to sell these abbreviated test tapes for what they cost me to guys who want to borrow my D-110 tape. These little jobs sell for only a couple of bucks apiece, which is not much more than the cost of the raw, unrecorded tape; yet one of them will allow the owner to find out a surprising number of things:

"First, since the timing beeps are recorded exactly seven minutes apart at normal tape speed, the user of a D- 210 tape can tell if his recorder is moving the tape too fast or too slow. With the 5000 cycle tone and the instructions sent with the test tape sampler, he can find out if his playback head is in proper alignment - something that is very important if he wishes to play the new pre-recorded tapes that are becoming so popular. To get the most out of these tapes, the head must be properly aligned. At the same time he can satisfy his curiosity as to just how good his recorder will sound when playing one of these high-fidelity tapes. If, before this time, he has only heard his recorder play music he recorded himself, he may be in for a pleasant surprise. Still more, the little sampler gives him a chance to examine and test the new thin tape that looks as though it will rapidly replace the 1.5 mil type for most applications. And finally - a most important consideration - if he happens accidentally to erase a part of this short test tape, the cost of replacing it will be but a fraction of what it would be if he had erased a portion of a professional test tape."

"I get it," Barney said. "You're just taking out insurance on your precious D-110 tape. Now, not to change the subject, I wonder if you can clear up a little mystery that has been bothering me. I've noticed several times that after we've replaced a picture tube the customer will call in and say that he believes the new tube has more snow than the old one had before it went sour. I notice you don't argue with him, but you simply say to keep an eye on the new tube for a few days and call again if this condition doesn't go away. Now why should a new tube have more snow and why should this snow disappear after the TV set has been running a few days?"

"There are a couple of things involved. In the first place, a new picture tube loses a substantial portion of its brightness during the first few hours of operation and then levels off to normal brightness that lasts pretty well for the life of the tube. This first abnormal brightness has a tendency to exaggerate any tiny amount of snow that is present. Secondly, the tube we took out was probably pretty dirty and any fine flecks of snow probably would have been obscured by the coating on the face of the tube. The new tube, on the other hand, has a nice clean face, and the owner can see even the tiniest specks of light that show up on it. You'll recall that customers sometime complain of increased snow when all we have done is clean the face of the tube and the safety glass in front of it."

"I suppose after a few days the abnormal brightness of the tube subsides and the face of it gets a little dirty and the 'increased snow' disappears and we hear no more from the customer."

Barney picked up from the bench a little coil that had a couple of leads with small clips on their ends soldered to it. "Hey, Boss," he said, "here is a little thing I've been using lately that I think, with all due modesty, is terribly, terribly clever of me."

"Doesn't look like much from here," Mac commented disparagingly. "All I can see is one of those slug-tuned antenna-substitute coils with a pair of test leads soldered to it."

"That's what it is," Barney admitted, "but the clever part lies in the use to which I put it. Loop antennas fastened inside console cabinets have always presented a problem when it is necessary to remove the chassis and take it to the shop for repair. Quite often they are hard to remove and replace; yet the set will not play satisfactorily without a loop antenna. That means we cannot check the operation of the set across the entire broadcast band unless we have the loop.

"I used to unscrew, unbolt, and unstaple the loops and bring them in, even though this meant a lot of extra work and there was always the danger the loop coils might be damaged while they were being lugged around. Old Barney does this no longer. He simply clips this little coil across where the loop leads connect and tests the set to his heart's content. The 'Loopstick,' as it is called, will replace any high-impedance loop quite nicely. Of course, it cannot be used as a substitute for a low-impedance loop, but a large loop of wire will do nicely for that; or you can usually get good reception on such a set simply by clipping a long antenna to one of the low-impedance loop connections."

"What do you do about alignment?"

"I align everything I can right on the bench," Barney explained. "Then, when I return the chassis, I carefully align the trimmer that tunes the loop fastened in the cabinet. Lots of times this trimmer is right on the loop itself; but no matter where it is, I align it with the chassis in position in the cabinet. That is a much better way of doing it than it would be if I brought the loop along and aligned this trimmer while the loop was lying on the bench or dangling by its leads."

"Good boy," Mac applauded. "I do believe that you have that little lazy streak that is always hunting a better-and of course, easier-way of doing things that marks a good mechanic in any field; but just always be sure that the new way is better."

 

 

Posted April 16, 2020


Mac's Radio Service Shop Episodes on RF Cafe

This series of instructive 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 Radio & Television News magazine (which itself started as simply Radio News), and then changed its name to Mac's Service Shop after the magazine became Electronics World. 'Mac' is electronics repair shop owner Mac McGregor, and Barney is his eager, if not somewhat naive, technician assistant. 'Lessons' are taught in story format with dialogs between Mac and Barney.

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