|
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
 By 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.
|
