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RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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|January 1950 Radio & Television News|
These articles are scanned and OCRed from old editions of the Radio & Television News magazine. Here is a list of the Radio & Television News articles I have already posted. All copyrights are hereby acknowledged.
I usually learn something new with each episode of Mac's Radio Service Shop, but not necessarily related to electronics. Such is the case this time where after Mac gives Barney a quick lesson in how to determine a transformer's winding turns ratio when needing to create an impedance match circuit. He then, while discussing whether 'free' repair estimates are truly free or of any real value at all, he uses the phrase 'a horse on you.' Maybe it is because I don't frequent bars that I had never heard that, but after a little research I now know it refers to a bar dice game called 'Horse.' 'A horse on you' is when you lose the final round of a 2-out-of-3 challenge. 'A horse apiece' is when you and your opponent each win one round in a 2-out-of-3 challenge. And now you know... the rest of the story.
By John T. Frye
Only a coal dealer could have seen anything good about the bleak January day. Before daybreak a mixture of rain and sleet had begun to fall, and now at nine o'clock in the morning it was still hissing against the window of Mac's Radio Service Shop and slowly but surely coating everything outside with a sheath of ice.
Inside, though, things were proceeding quite normally. As usual, Barney was trying to beguile some information out of Mac, his boss.
"- and so," he was saying, "when I started to build this little phono-amplifier for Margie, I needed an output transformer. I found those three on the bench there in my parts collection, but they have no name on them. There's no way of knowing whether any of them will match a 6K6 to my four-ohm voice-coil. Unless you know what impedances an output transformer was designed to match, you might just as well not have the transformer."
"Well, now, I wouldn't say that!" Mac exclaimed in a startlingly-good imitation of Gildersleeve's Peavy.
Without further comment he clipped a couple of test leads to the secondary of one of the transformers and then inserted the other ends of the leads in the filament-pin holes of the four-prong socket of the tube tester. With the v.t.v.m. across these leads, he manipulated the filament voltage switch and the "line voltage adjust" control until he had exactly one volt across the voice-coil winding. Then he measured the voltage across the primary winding.
The procedure was repeated with the other two transformers, care being taken each time to see that exactly one volt was applied to the normal secondary. The primary voltage readings were respectively 30, 35, and 43.
"If you put an a.c. voltage into one winding of an unloaded transformer and measure the voltages appearing across both windings, the ratio between these two voltages is very nearly equal to the ratio of the number of turns of wire on each of the two windings. Since our v.t.v.m. does not load the windings," Mac went on, "we can safely figure that the secondary-to-primary turn ratios of these three transformers are 1/30, 1/35 and 1/43."
"Very interesting, professor," Barney applauded, "but so what?"
"So-o-o-o, there is a connection between the turns ratio of a transformer and the impedance ratio of the windings. It is given by this formula," Mac said as he scribbled on the blackboard at the end of the bench: N =
"N stands for the secondary-to-primary turns ratio; Zs is the impedance to be used across the secondary; and Zp is the impedance or plate load resistance presented by the primary. If we substitute the turns ratio of the first transformer and the four-ohm impedance of the speaker you intend to use across the secondary, we get:
"Squaring both sides gives us: 1/900 = 4/Zp.
"When we 'cross-multiply,' we end up with Zp. = 3600 ohms. Using the same method, we find that when the other two transformers are used on a four-ohm voice-coil, they will have primary impedances of 4900 and 7396 ohms. What was the load resistance of your 6K6?"
"It was 7600 ohms; so that number three job will be very fine business. Now why didn't I think of that?"
"Probably because you were too busy scheming how you could get me to do the work for you," Mac said dryly. "I suggest you write the turns ratio on each of the transformers. Then if you ever want to know if one of them will work in a particular spot, you can figure it out."
"Check!" Barney said as he carried out the suggestion. "And while you are in such an informative mood, I'd like to ask you something else: what do you think about giving free estimates on radios? I see where a guy across town is advertising this feature."
"I feel about the free estimate as the New England preacher felt about sin:
I'm 'agin' it," Mac said promptly. "In the first place, if you will think the thing clear through, you will see that it is neither 'free' nor an 'estimate.'
"What you have to keep in mind," he went on, "is that a service technician has just so many hours of work to sell each week. His income depends directly upon the time he spends with a hot soldering iron in his hand. If he gives some of this time away for free, he simply must get more money for the working time left. That means that the cost of the 'free' estimate is simply passed on to the other customers in the form of higher charges."
"Does making an estimate take much time?"
"If it is of any value, it does. Finding what is wrong with a radio is always the thing that takes both brains and time. Fixing it is usually accomplished by a few passes with the diagonal cutters and the soldering iron. Before you can say how much it will cost to repair a set, you have to restore it to good playing condition. That means tubes must be checked, defective parts located and removed and new ones 'tacked' in place, circuits must be aligned, etc. If these things are not done, your estimate is nothing more than a guess."
"Well, what's wrong with that? It is an estimate, you know."
"Yes, I know, and you know, but the customer doesn't. To him an 'estimate' is actually the determined cost of putting the set into first class shape. Of course, if you find out that you have made a mistake and the bill is less than you anticipated, he is delightfully surprised; but if the cost is more than you calculated, he definitely feels that is a horse on you."
"The thing to do, then, is to make the estimate plenty high."
"That is exactly what happens in free estimating, because the estimate must be made quickly. Not much time can be squandered on a free service. Even a veteran service technician, though, never knows when what looks like a simple blown bypass condenser job will develop a noisy i.f. or output transformer when the set is thoroughly warm; or even a warped speaker cone may show up at this time. The only thing to do is to make the estimate high enough to cover such possibilities.
"That way of doing business places a heavy strain on the service technician's ethics. After the customer has indicated that he will hold still for the higher charge, there is always the temptation to let that figure stand, even though the repairs needed do not warrant it. The service technician can always quiet his conscience by telling himself that on the next job matters will probably be reversed and he will take the licking. A technician I know argues, 'If you lose on the popcorn, you gotta make it up on the peanuts.' That's no good. There is no such thing as 'averaging up' your honesty. Either you shoot square in every little detail or quit trying to claim you are an honest man."
"Any more reasons why you are so fond of free estimates?"
"Plenty of 'em. The practice encourages slipshod work. If the service technician feels forced to stay inside a hastily-given estimate, he is quite likely to try to patch or cobble up some repairs that were not foreseen or provided for in the price quoted."
"But the practice does bring in business, doesn't it?"
"I have never been convinced that it does-at least not the kind of business you want. It does attract the 'shoppers,' the something-for-nothing individuals, and the characters who believe that all service technicians are automatically cheats and swindlers; but people in general have come to distrust 'free' offers. The word has come to be associated with cheap, come-on tricks in advertising. You yourself, know the kind of offers you usually get in second-class envelopes that have the word FREE! plastered all over the outside in big red letters."
"Why is it that every now and then it radio parts manufacturer comes out in favor of free estimates?"
"It is easy to play Santa Claus with someone else's time or money. Can't you just hear the manufacturer scream if we suggested he give away some of his tubes or resistors or condensers? Very, very few of the veteran service technicians with whom I have talked are in favor of free estimates. They say that when doctors start giving free diagnoses, they will start giving free estimates, but not before. They argue that the radio service business has enough headaches in it now without adding those that are a part of free estimating."
"Then you think the birds who give these estimates are dopes?"
"Oh me!" Mac sighed. "I did not say that. That is the trouble with being young: you cannot be sure you are right unless you can prove someone else is wrong! In some cases and in some localities, free estimates may be a good thing. I do not know. All I know is that I do not like them or intend to give them. We charge a flat minimum for making an estimate; but we do a good, thorough, unhurried job of finding everything that is wrong with a set and the cost of putting it right. There is no padding of the estimate to take care of overlooked items, because we have taken the time to make a careful survey of the set. We could afford to take this time because we were being paid for it. The estimate is well worth our customer's money for it gives him an accurate figure upon which he can depend in deciding whether he should have the set repaired or buy a new one."
"In short," said Barney with his flair for slogans, "all we 'give' our customers is a square deal - but who wants anything more ?"
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive stories was the brainchild of no 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.
Posted September 16, 2015