|
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
 By
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
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.
|
