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Mac's Radio Service Shop: Tape Recorders
March 1954 Radio & Television News

March 1954 Radio & TV News
March 1954 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.

Webster Electric Ekotape Model 205 Tape Recorder - RF Cafe

Webster Electric Ekotape Model 205 Tape Recorder (eBay image)

As mentioned in the past, most things you might want to find from the present or past can be found eventually on eBay. Such is the case with the Webster Electric Model 205 Tape Recorder mentioned in this Mac's Radio Service Shop episode which appeared in a1954 issue of Radio & Television News magazine. Here, Mac McGregor schools sidekick electronics technician Barney Jameson on the workings of a high quality tape recorder, including some of the ingenious methods devised for test and alignment. I especially like the magnetic tape specifically prepared for head alignment by the Toogood Recording Company of Chicago (yes, it was a real company, named after Mr. Louis S. Toogood). The recorded signal is 0.001 inch in wavelength and will reproduce at 7500 cycles-per-second at 7.5 i.p.s. or 15,000 cycles at 15 i.p.s. (i.p.s. = inches per second). Tape machines were getting very popular in the 1950s as prices came down and quality went up. Through the 1970s, just about every issue of electronics hobby magazine contained articles and advertisements for magnetic tape machines and accessories. 

Mac's Radio Service Shop: Tape Recorders

Mac's Radio Service Shop: Tape Recorders, March 1954 Radio & Television News - RF CafeBy John T. Frye

The express truck was just driving away from the service shop as Barney returned from his lunch hour, and the youth, who had more curiosity than Dr. Kinsey, immediately hurried inside to find out what new equipment Mac could be purchasing. The boss already had the instrument out of the box and sitting on the service bench, and he was unwrapping some small parts that had been packed with it.

"Hey!" Barney exclaimed, "that's a mighty neat looking tape recorder. Is it for the shop?"

"Yep," Mac answered. "Our old one is pretty well worn out; furthermore, home tape recorders have improved a lot since that one was made. The features of this Ekotape 205 represent many of the advances found in most late model recorders."

"Such as ... " Barney led him on.

"Such as the ability to record at either 3.75 or 7.5 inches-per-second and being able to switch instantly from one speed to the other with proper equalization of the playback amplifier being cut in automatically for either speed. It is a dual-track machine that can put two full hours of program, on a seven-inch reel and has a fast forward and rewind for quickly spotting a particular section of the recording. When a program is being taped, it can be heard through the recorder, speaker or this can be cut out. There is a full range tone control for boosting either the bass or highs during playback. There is a high-level input jack and a patch cord for taking a recording from any radio, TV, or phono player by simply clipping the ends of this cord directly to the voice coil connections. The same jack, of course, could be used with a shielded cord for taking the program from a high impedance source, such as directly across the volume control or from the output of a phono cartridge.

"As I mentioned, many of these features are found in practically all late model recorders; but here is something in this one that appeals to me for our uses." As he said this, Mac inserted a small device in an opening in front of the recorder and pushed it gently with his thumb. Instantly the reels that had been moving the tape through the recording head stopped going around. As his thumb released the gentle pressure, the reels started revolving again.

"This manual control of tape movement allows you to stop and start the tape instantly at any time while recording or playing back without disturbing any of the other controls. I figure it will be most handy for dictating. A fellow can say a sentence and then stop the gadget while he thinks up another."

Mac removed the hand control and inserted the end of a flexible tube that went down to a foot treadle affair resting on the floor. When he pressed on this with his foot, the tape could be stopped and started again as readily as with the hand control.

"This foot control is a good companion for the hand control," Mac explained. "It allows you to control the recorder while your hands are busy doing something else. For example, Matilda can use it to take down on the typewriter a letter I have dictated on the tape. She can let the tape run for a few words at a time and then hold it while she puts these down, and so on."

"You whizzed something by me awhile age," Barney complained. "What was that business about different amplifier compensation for each speed?"

"Well, you must know the response curves of an uncompensated tape recording would never serve as a high-fidelity fan's pin-up. It looks like a sort of lopsided parabola with the lows falling away from the peak more gradually than do the highs. By increasing the speed of the tape, we can increase the frequency of this peak response point. In fact, the relationship is a direct one, with the peak response frequency being doubled by doubling the tape speed."

"Hold it!" Barney commanded. "Why?"

"Suppose we used light-sensitive tape instead of magnetic and employed a neon lamp shining through a narrow slit on to the tape as our recording head. When the light was bright, the tape in front of the slit would be turned black; when the light was out, the tape would remain white. Now if we use a low-frequency sine wave to excite the neon lamp, the moving tape will be transformed into alternate bands of white and black. As we increase the frequency of our exciting signal, the width of these bands will decrease until they become narrow vertical lines. Finally, as the frequency goes higher and higher, the alternate lines of black and white will become so narrow that they merge together. Holding our exciting frequency at this point, however, we can double the speed of the tape and so double the width of the lines, making them again easily distinguishable. Only when the exciting frequency is doubled will they merge together once more. Since the recording head prints magnetically on the tape in precisely the same way that this apparatus would print photographically, you can see why increasing the tape speed increases the potential high-frequency response."

"Yes, and I also see why different amplifier compensation would be required to flatten out the curves for each speed. You would need less high-frequency compensation at the higher speed. Right?"

"Right," Mac applauded; "and while this picture is still fresh in your mind, perhaps we had better talk about the importance of head alignment in playing tapes recorded with a recording head that is different from the playback head. Since most home recorders use the same head to perform both jobs, this is not very important as long as the machine is used only for playing tapes recorded on that machine'; but now it looks as though we are on the brink of a new era in which there will be a lot of exchanging of tapes."

"What makes you think so?"

"For one thing, it is becoming quite a fad to exchange tapes between recorder fans. In fact there is an organization called Tape Respondents, International, with headquarters in San Francisco, that encourages just that 'sort of thing. Then I saw in 'Time' a few weeks back, where both Pentron and Webcor were planning on releasing pre-recorded tapes of classical music."

"Why does a head not in alignment hurt?"

"Suppose we want to play that photographically printed tape we were talking about," Mac said. "Let's say our playback mechanism consists of a bright light shining through a very narrow slit onto the tape and that this reflected light excites a photo-electric cell that works into our amplifier. Light falling on a white section of tape excites the cell to maximum; when it falls on a black section, the excitation is minimum. When a low frequency recording passes the slit of light, the output of the light cell swings back and forth from a maximum to a minimum at a rate that faithfully reproduces the low note.

"Suppose, though, that we try to reproduce the frequency that printed the tape with the finest distinguishable lines. If the slit through which the light shines is in precise alignment with the lines themselves, the reflected light will be turned on and cut off cleanly by the movement of the fine lines beneath the slit. On the other hand, suppose the slit is canted so that it makes an angle with the lines. Now, long before we reach a frequency at which the lines themselves run together, the slit of light will cease to fall entirely upon a single white or black line. Instead; it will fall across adjacent lines so that part of a white line and part of a black line will always be beneath the slit. That means that the reflected light can never rise to the maximum or fall to the minimum value it attained when proper head alignment allowed all the light to fall upon a single white or black line. In other words, improper head alignment results in a loss of high frequencies. Of course, if the same head is used for both recording and playback, then alignment will matter little, for the recorded lines will have to match the angle of the head, even though both are tilted from the vertical."

"How do you know when a head is in proper alignment?"

Before answering Mac opened a cabinet and took out a roll of tape on a special 5" reel.

"This," he said, "is an alignment tape specifically prepared for head alignment by the Toogood Recording Company of Chicago. The recorded signal is 0.001 inch in wavelength and will reproduce at 7500 cycles-per-second at 7.5 i.p.s. or 15,000 cycles at 15 i.p.s. The signal is vertically aligned on the tape to a tolerance of 1 1/2 minutes of arc. While the tape has been recorded the full width, it can be used effectively on dual-track machines because great care has been taken to make sure the edges of the tape are cleanly recorded. This is necessary since many half-track heads run over the edge of the tape and would give a false reading if the recording at the edges was inaccurate.

"To align the head of a home recorder, you simply play this tape at 7.5 i.p.s. and adjust the position of the head by the means provided until maximum output is indicated by an audio wattmeter inserted in the external speaker jack or by an ordinary output meter connected across the speaker voice coil. Let me say here and now, though, if you ever erase a single foot of this tape, you had better take to the hills. Furthermore, never rewind the tape or run it forward at high speed for fear of stretching it. After you are through making your alignment test, reverse the reels and let the tape wind back on this reel at playing speed."

"Is there anything else I ought to watch in working on recorders?"

"One thing comes to mind. I note some manufacturers specify carbon tet for cleaning rubber drive wheels and others say to use alcohol. Probably the cleaning agent recommended depends on the kind of rubber used, and any other cleaner may soften or damage the rubber. Always stick exactly to the cleaner recommended in the service data.

"In general, never let a recorder go out without cleaning the head thoroughly. This is something home recorder owners are likely to overlook, and it has tremendous effect on the quality of the recording. Check tape speeds with a timing tape. After this has been running for a few seconds, count the proper timing intervals that pass a certain point in exactly a minute. If the speed is off more than one full interval in this length of time, find out why. Always check all tape moving controls thoroughly, making sure they work easily, that the tape is stopped without putting excessive strain on it, and that there is no tendency to spill the tape.

'''Make a short recording at an excessively high level and see if the erase head will take this off completely. If not, measure the erase voltage delivered to the head and compare this with what the service data says it should be. If that is all right, make sure the tape is held firmly against the erase head by the pressure pad. If nothing is wrong here, you are probably up against a bad head. Substituting a good head is the best test for that."

"How about checking for wow?"

"Special equipment is needed to measure wow accurately, but you can easily make a rough check by recording a frequency of about one-thousand cycles and then listening to it being played back. You are almost certain to hear some wow on home recorders, but it should not be very pronounced. You will soon learn how much to expect.

"A rough frequency check can be made by recording a good record containing a wide range of sounds. A good piano piece constitutes a tough test. If this sounds good on playback, the recorder response may be considered satisfactory. For a better test, record 1000, 50, 100, 500, 1000, 2500, 5000, 7500, and 10,000 cycles in that order from our audio generator, keeping the input level constant as measured with the a.c. v.t.v.m. Plug the audio wattmeter into the external speaker jack with the proper load resistor switched into use. Now, with the first 1000 cycle note being played, set the volume control so that a convenient value of output is obtained well below the maximum output rating of the amplifier. One watt should be satisfactory. Note down the reading produced on the wattmeter by each frequency. The departure of these values from the 1000-cycle reading can be converted into decibels and compared with the manufacturer's claims. Of course the tone control should be in the 'flat' position while taking the readings."

"You must be expecting to do quite a bit of recorder service."

"I am. RCA predicts that schools alone will buy 50,000 tape recorders this year. More and more families are finding new uses for them around the home. I consider them easier to work on than record changers. One reason I bought this new job for the shop was so that we would have a reasonable standard of home recorder performance always at hand. On top of that, it is sometimes a great help to be able to play a recording made on a doubtful machine back on one known to be good, and vice versa. This allows you to spot whether the trouble is in the recording or playback system, or both. Now here are some good books on tape-"

"Oh no you don't!" Barney shouted.

"You've already made a bookworm out of me by loading me down with those now-here's-something-you-ought-to-read things; but I'll be darned if you're going to make a tapeworm out of me!"



Posted April 27, 2021

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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