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Mac's Radio Service Shop: A Sound Conversion
November 1951 Radio & Television News

November 1951 Radio & TV News
November 1951 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.

A November edition of "Mac's Radio Service Shop" is appropriate given today's date, especially since author John T. Frye nearly always had the story's setting coincide with the month in which it appeared in Radio & Television News magazine; the year was 1951. The unspecified dateline is somewhere in the upper Midwest, most likely Indiana. Mac's mention of converting a black-and-white television set to color by installing a "color wheel" really betrays the era. The NTSC (National Television System Committee) had not yet adopted an industry standard for color TV, and the various manufacturers were selling a mix of mechanical, electro-mechanical and all-electronic sets. In 1953, the NTSC settled on a 525-line interlaced scan (only 468 lines are part of the visible scan). Knowing that a better color system would be available soon due to massive public demand, Mac put his efforts into talking customers out of a color conversion and into a sound system conversion in order to vastly improve the lame speaker and amplifier setups which came standard in most sets.

Mac's Radio Service Shop: A Sound Conversion

Mac's Radio Service Shop: A Sound Conversion, November 1951 Radio & Television News - RF CafeBy John T. Frye

The warm, soft air blowing through the open door of Mac's Radio Service Shop and gently rustling the pages of the calendar on the wall seemed to be mocking the month of November displayed. Of course, a pessimistic observer could, if he tried, pick out signs that summer had almost run its pleasant course: there was a sharp odor of burning leaves on the lazy air; the slanting shafts of light piercing the shop windows came from a sun already far south of the equator; a little boy strutted up and down the alley behind the shop with his head thrown far back so that he could see through the eye-openings of the grotesque, ill-fitting Halloween mask he wore - but who was so foolish as to look ahead from the midst of a wonderful Indian summer? The wise man lived each golden day for itself alone, nor spoiled its enjoyment with morbid thoughts on the winter to come.

Certainly the two wise men inside the shop were entirely taken up with the present. Barney was sweating and mumbling to himself as he tried to get a TV chassis out of its cabinet, and Mac watching him with an amused grin.

"What's your trouble, Little Chum?" Mac finally asked. "You're mumbling in your chin-fuzz like an old maid catching her first glimpse of a modeled Bikini swim suit."

Aw, it's this alleged conversion job. Just look at it! The deflection yoke is nailed to a fence-board that, in turn, is nailed to the sides of the cabinet. The tube is held in by an iron ring that is nailed to the front of the cabinet. Getting the works out all in one piece is about as easy as trying to carry a two-bay conical through a revolving door."

"Sounds like you're 'agin' converted receivers."

"Just some of 'em. The ones that are well-planned, both mechanically and electronically, are all OK; but I certainly don't go for cobbled-up affairs like this one. Why, the service charge will have to be double what it would have been if the set were easy to take out and put back. Personally, if I had a smoothly-operating, well-designed, easily-serviced ten- or twelve-inch set, I'd think a long time before turning it over to a nail-happy wood-butcher like the joker who perpetrated this mess. It convinces me that the words 'bigger' and 'better' don't always go together."

"Ah, so young to be so bitter!" Mac murmured mockingly; "and while you're rationalizing, don't forget that your small-screen set will be just the ticket for a color-wheel conversion. I'll grant you, though, that some of the converted jobs that have been trickling in here are pretty awful. I think the main trouble is that we technicians are so wrapped up in the electronic problems involved in a change-over that we are impatient with the mechanical demands of the operation. Being eager to see if we are going to have sufficient linear sweep, etc., we do not give enough thought and planning to make the project mechanically strong and easily-serviced. This short-sighted attitude, carried to an extreme, breeds cases like the one you are admiring there.

"It is rather a coincidence, though, that just a couple of nights ago I talked my friend, Ed Beck, out of a big-tube conversion. That twelve-inch table model of his has always put out a mighty fine, linear picture; it is soundly engineered; and it has never given him a moment's trouble. The guys at the plant where he works, however, have been feeding him a line about a twelve-inch getting only the center portion of a televised scene, while a seventeen- or twenty-inch tube gets it all.

"It is surprising how many people wonder about this," Mac went on. "I remembered that Ed is a 'shutter-bug,' though; so I explained to him that using different-sized kinescopes was exactly the same proposition as making different-sized projection enlargements from the same identical negative. Each size of tube shows exactly the same scene as the other, but the bigger tubes just 'blow up' the picture to greater dimensions. When Ed grasped this idea, he promptly lost interest in getting a bigger tube, for he knows that the greater the enlargement the greater must be the viewing distance for a pleasing appearance; and his home will not permit the screen to be watched from much more than a dozen feet. So-o-o-o, I talked him into a sound conversion instead."

"What do you mean, 'sound conversion'?" came Barney's muffled inquiry from inside the TV cabinet.

"Just what I said. The sound on Ed's set is as poor as the picture is good. A single pentode drives a six-inch speaker mounted right in the top of the cabinet - and incidentally that cabinet has a nasty resonant peak at around three or four hundred cycles. When the Philharmonic is playing on the picture screen, you'd swear it was the Corn-Juice Trio down at the Dutchman's if you judged by the sound alone."

"What do you intend to do about it ?"

"Already done it. I sold him a good but reasonably-priced coaxial speaker mounted in a reflex cabinet that sits right beside the stand that holds the TV set. A ten-watt hi-fi amplifier rests on a small shelf on the back of the speaker cabinet, and a switch at the rear of the TV set permits the output of the sound detector to be sent through a short shielded cable to the amplifier or to be passed through the set's audio system to its own speaker."

"Why that arrangement? Surely Ed won't want to listen to that six-inch speaker after he hears the coaxial."

"Two reasons: First, I want him to hear the difference between the two reproducing systems, and I want him to be able to demonstrate - as I know he will - this difference to his friends and so win other sound conversion prospects for us, Secondly, if the need arises, the TV set is still a complete unit and can be used by itself, in say a sickroom, where there would not be room for the speaker cabinet; or, if the speaker and amplifier are in use somewhere else, the TV set will not be put out of commission."

"How would the amplifier be in use somewhere else?"

"Well, I showed his daughter, Mary, how she could plug the pickup of her little three-speed table-model record-player into the amplifier; and she had not heard a dozen bars of her prized Stan Kenton's September Song platter coming out of that coaxial speaker until she began making big plans for having a 'platter party' down in the rumpus room so that the kids could hear 'how good SK really was.' Personally, I'm convinced that gal is mad as a hatter. She kept playing records and wanting me to listen for 'that dog house growling' or 'the hot licks of that licorice stick'."

"You're just not hep, Grandpa," Barney said as he pulled his head out of the TV cabinet and turned a very dirty but grinning face up at Mac. "But tell me what other arguments you used to twist the poor man's arm."

"Well, I pointed out that buying a high fidelity sound system was really a fine investment for the future, no matter which way television might turn and twist. Color sets, v.h.f. sets, sets with three-dimensional viewing - no matter what the engineers cook up in the way of receivers, the sound will finally have to be amplified and reproduced; and Ed can be sure the outfit he bought will do a fine job of that, no matter what sound source he feeds into it. Also, he will be able to buy comparatively inexpensive table model sets and still have sound reproduction far better than most expensive consoles would give him. Another less-important consideration is that keeping the speaker away from the chassis will eliminate any microphonic-tube troubles."

Mac stopped for breath and then continued:

"A nice part of buying a sound conversion from the customer's point of view is that he does not lose the money he puts into it when he finally discards the television set to which it was attached. From our point of view, of course, sound conversion has many advantages over tube conversion: it is easier to do, and the results are almost as startling. The cost can be figured exactly in advance, and the customer can see what he is getting for his money. All of the work is electronic work and can be done right here in the shop. We neither have to turn ourselves into cabinet-makers to do it or hire a cabinet-maker to finish the job.

"Another great advantage might be termed psychological. In the case of a tube conversion, as we sadly know, the customer sees what looks like very drastic changes made in the set itself, and he is all braced to discover that we have 'messed up" his receiver. He seems to feel that once we have done a tube conversion on his set we are responsible for anything that happens to it from then until eternity. We can explain until we are black in the face that the only changes performed were in the sweep circuits; he still holds us responsible for everything from a dead r.f. tube to an open voice coil in the speaker.

"This is not true in sound conversion. All that is done to the set is to add the change-over switch and possibly to mount an outlet socket at the rear so that the set switch can also turn the amplifier on and off. The rest of our conversion is clearly separate from the set itself. Only when trouble develops in the speaker or amplifier are we called upon to 'daddy' it. On top of that -"

"Enough! Enough!" Barney shouted, holding up his hand. "That sales talk of yours has more verses than 'Mademoiselle from Armentières.'"

"No wonder poor old Ed gave in."

"And now, if you can descend from the sublime to the ridiculous, how's about getting your gloves, goggles, and crowbar and helping me pry this tube-retaining ring loose from the cabinet. I've fiddled with it until I'm as jittery as though I'd been de-fusing a block-buster."



Posted November 25, 2020

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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