The Smith-Kettlewell Technical File
A Quarterly Publication of
The Smith-Kettlewell Eye Research Institute’s
Rehabilitation Engineering Research Center
William Gerrey, Editor
Issue: SKTF -- Spring 1982
Original support provided by:
The Smith-Kettlewell Eye Research Institute
and the National Institute on Disability and Rehabilitation Research
Note: This archive is provided as a historical resource. Details regarding products, suppliers, and other contact information are original and may be outdated.
Questions about this archive can be sent to
TABLE OF CONTENTS
Splicing and Editing Open-Reel Audio Tape
Soldering (Part V), RCA and Motorola Plugs
SPLICING AND EDITING OPEN-REEL AUDIO TAPE
by Eric Clegg, Jay Williams, John Baker, Bob Waterstradt and Bill Gerrey
This article discusses tape splicing with both automatic tape splicers and hand-operated editing blocks, along with pros and cons of each method. In addition, techniques for cutting and rejoining tape at desired points for editing are presented.
Of Historical Interest
Recording tape, much as we know it today, was being used in Germany before World War II. As early as the mid 1930's, Telefunken had designed a "magnetophone" which used acetate-based tape. The discovery of this machine by the allies at the end of the War cleared up mysteries surrounding the fidelity and flexibility of certain German Wartime broadcasts.
The flexibility afforded by the tape-recording magnetophone was extraordinary compared to that of systems used elsewhere in the world. Sound recording was either being done on disc records, or was magnetically recorded onto
thin stainless steel wire. A sort of corrective editing was being done on lacquer discs by highly-skilled operators who could set the recording stylus back into previously made grooves so that a section of the disc could be rerecorded. Recording wire could be cut and rejoined as desired by tying it in square knots. These splices were not entirely noise-free, and the fact was that successive layers of wire were in direct physical contact on the spool, causing a great deal of "print through"
(adjacent wraps recorded on to each other) making this medium very noisy
in general. Noting the superiority of tape recording, Ampex (a prominent manufacturer of precision electric motors during the War) recognized the opportunities for peace-time business in making tape machines. By 1947, such machines
as the Ampex Model 200 and ,the Brush "Miraphone" were in production.
The manufacture of tape was somewhat more troublesome; even through 1947, we were using BASF tape captured from the Germans in major productions such as the Bing Crosby Show. (The finalized German product "Luvatherm" used a polyvinyl chloride base which was homogeneously impregnated with ferric oxide; recording could be done on either face.)
Our plastics industry had some catching up to do before we could make new tape. In the confusion, even paper tape was issued as an inexpensive substitute for the good stuff (something the Germans had tried and abandoned by 1934).
The first major break for tape, if you'll excuse, the expression, came with the editing of Bing Crosby's Radio Show. Crosby hated timed radio shows and he was in constant battle with the network over this issue of timing. For his live audiences, he had a two hour vaudeville formula which worked; timing is enough of an issue for a performer without having to rigidly fix the time of the show.
In 1947, Jack Mullin, promoter of the captured magnetophone and the father of tape recording, stepped in with an answer to Crosby's prayers. The great entertainer could now do as he pleased, and the
"timed" show could be edited in a laboratory. Even the German tape was of varying quality, and the story goes that
Mr. Mullin spent many "happy?" hours recording and listening to tones on various pieces of tape in order to collect consistent batches of the material to do the Crosby Shows.
Editing was done by cutting the tape and splicing it with cellophane tape. At first, the tape was simply cut with scissors and rejoined freehand. Noise in a splice is lowest when the cut in
the tape is at an angle. Since the angle of a freehand cut was unpredictable
(freehand joining of the tape led to azimuth distortion and flutter as the splice passed through the machine), splicing tools were soon designed to eliminate these problems. (Smoothly-running splices were even more important because, with a finite supply of captured German Luvatherm and other substitutes, one was obliged to reuse the already much edited tape.)
A noise-free splice has the following properties:
- The cuts in the tape are clean and are consistently made at the same angle.
- No space exists between the ends being joined. Any space which does exist constitutes a break in the program material, in addition to which the exposed stickiness of the splicing tape can pick up stray flakes of oxide carrying magnetic information of its own.
- The splice is secured by "splicing tape" made for this specific purpose.
Common varieties of adhesive tapes have the following disadvantages:
- They are made with a celluloid base which becomes brittle with age.
- Their adhesives are excessively sticky and tend to flow (bleed out
from between adjoining surfaces). Splices made with these adhesives gum up the heads and cause flutter as they pass through the machine. In addition, excess adhesive tends to stick adjacent layers of tape together on the reel.
Proper splicing tape is designated as "low cold flow" (LCF) and employs a polyester or Milar base. Rolls of splicing tape come in various widths.
That which is intended for use with hand-operated splicing blocks, such as the "Edi-Tall Block", is 7/32 in. wide--slightly narrower than the 1/4 in. recording tape. Those wider than 7/32 in. are used for automatic tape splicers such as the Robins "Gibson Girl".
Splicing tape also comes in a pre-cut form; one such product is called "Edi-Tab", designed specifically for use with the "Edi-Tall Block". In this form, a number of pre-cut lengths of 7/32 in. splicing tape, together with bits of backing material, are affixed to a card. First, a tab (which contains a 1/2 in. length of splicing tape having its non-sticky side attached to a bit of adhesive backing termed the" "carrier") is peeled off the card. This tab is then used to secure the splice in the block, after which the backing material is peeled off the splicing tape. In other words, the backing material ("carrier") serves as a handle for the little section of splicing tape.
Whereas in theory the above tabs seem clever, none of these authors report that they have any benefit to the blind user. The little section of splicing tape under the backing is hard to position directly over the splice, and removal of the backing material often wrinkles the splice.
Splicing tape is very susceptible to changes in humidity and temperature. Therefore, it is recommended that it be stored in a drawer and/or a plastic bag to prevent its exposure to varying ambient conditions.
These devices can be a Godsend for the occasional repairing of broken tapes or occasional non-critical editing. Without much practice, clean and precision splices can be done rapidly. However, these splicers have the following disadvantages:
- Tapes to be joined are overlapped under a diagonal cutting blade whose position is not clearly marked on
the splicer. Positioning the tape for very critical editing is difficult. (Your Editor uses "such a splicer on the master tapes for the "Technical File"; that's why there is an occasional w' 'issing.)
- These splicers require a lot of maintenance. If editing is being done constantly, on a day to day basis, it won't be long before these devices
give you headaches. With extended use, foam-rubber on the securing arms and between cutting blades becomes compacted and sticky, and the blades wear ever-deepening grooves in the cutting plate beneath the tape. Replacement foam pads, blades and cutting plates are available, but their replacement requires careful reshaping, gluing, and adjusting of the new parts.
- Deterioration of the foam pads and/or misalignment of the tape can cause splices to part during the editing process; the user may complain loudly in a repertoire of languages.
Given all the above, the convenience of automatic splicers and their quality of work (when everything goes right) justify the following discussion.
In the 1950's, Robins Industries marketed the automatic tape splicer which has become the standard configuration for all such devices. Not only is this instrument capable of consistently cutting the tape ends to a precise angle, it has trimming blades which cut away excess material along the edges of the tape after the joint has been made with a slap-dash application of over-sized splicing tape. To assure that these splices can pass easily through tape guides of the machine, the trimming blades are curved inward to give the splices an "hour glass figure". The Robins splicers became known as the "Gibson Girl Splicer" after the famous illustrations of turn-of-the-century women drawn by Charles Dana Gibson. (Models within the past 15 or 20 years have trimming blades whose curvature is drastically reduced so as not to damage the edge tracks of 4-track tapes.)
At first glance, this splicer looks somewhat like a stapler. Two channels for aligning the ends of the tape are located on either side of a cutting plate over which a large central stapler-like cutting arm can be brought down onto the plate. Behind each channel is mounted a spring-loaded arm with an attached foam-rubber pad to secure the recording tape in its channel. The blades in the cutting arm can be moved to either of two positions; the rear position is for cutting the recording tape at a 45-degree angle, and the forward position is for trimming off the excess splicing tape.
To cut and match up the two tape ends, place them one at a time into their respective channels so that their ends overlap on the cutting plate, holding them in place with the securing arms. Move the blade assembly to its rear position in the cutting arm and press this arm down firmly onto the tape. You will hear a distinct "chopping" sound as the angled blade cuts through both pieces of tape. As the cutting plate wears, the blade will tend more and more to cut through only one of the overlapping tapes; you will learn to recognize the difference in sound between a single "pop"
and the desired double "crunch" when both tapes are cut. Finally, briskly blow away the trimmed off ends of tape.
Splicing is done by gently laying wide splicing tape (running from front to back between the securing arms) across the
cut ends of the recording tape. Slide the cutting assembly to its forward position and again bring this arm down firmly. Raise all three arms to their upright position and try removing the spliced tape; doing this before clearing away the excess splicing tape will painlessly let you know whether or not the splice was trimmed completely. If the recording tape is reluctant to leave the splicer, bring down all three arms and try again.
Finally, peel off all excess splicing tape remaining on the splicer. Do this after you are absolutely sure that these pieces have been trimmed free of the recording tape--otherwise, pulling on attached excess splicing tape will misalign the splice and prevent precise re-trimming. Troublesome remnants of splicing tape can be removed by slipping the point of a Braille stylus under them just behind and in front of the cutting plate.
Depending on the make and model of automatic splicer, a tape dispenser may be attached just behind the central cutting arm. You may find that you prefer feeding the splicing tape into position from the front, holding the roll in your hand. Once it has been laid over the splice, you can unroll enough splicing tape to allow the cutting arm to come down behind the roll. After trimming, this excess tape can easily be retrieved and re-spooled. Using the dispenser on the rear makes it hard to gain access to the splicing tape without disturbing the ends of the recording tape, and you can badly cut your knuckles on the cutting blades when doing so.
Hand-Operated Splicing Blocks
The first splicing block was a bar of brass which had a simple 1/4 in. wide channel milled into it to accept the tape. A
45-degree saw cut across the bar permitted insertion of a razor blade to cut the tape. Blocks of this basic design can still be found; some have padded securing arms to hold the tape in position.
The "Edi-Tall Block", developed by
Mr. Joel Tall, is quite ingenious, and it has become the standard of the trade. It is an aluminum bar whose channel has undercut sides to accept the edges of recording tape. To use a machining term, the sides of this channel are "dove-tailed", i.e., the undercuts taper to a close just under the lip of the channel. As viewed from the top, the width of the channel is slightly less than 1/4 inch. After the tape is inserted into the channel, these dovetailed edges prevent the tape from leaving the block on its own accord. In fact, the dimensions of the channel slightly distort the tape so that a fair amount of friction must be overcome to alter the tape's position.
The channel has a curved bottom
which allows the user to press the tape down far enough so that its edges slip past the narrowed lips of the channel; the tape can easily be massaged into the channel. Although these blocks are optimized for 1-1/2 mil. tape (.0015 in. thick; 1200 feet can be spooled onto a 7 inch reel), tape of 1/2 mil. thickness (.0005 in., 2400 feet per 7 inch reel)
will work if care is exercised.
Finally, the "Edi-Tall Block" contains two cutting slots which are intended to accept a razor blade. The slot closest to the end of the block is at a 45-degree angle. The slot which appears more toward the middle is at either 90 or 60 degrees to the direction of the tape, depending upon the vintage and manufacturer of the block. In tape editing, 45 degrees is the standard cutting angle. Although the other slot can be used to make "rough cuts", it exists largely for historical reasons; it represents the distance between the play-back head and a convenient cutting point on vintage Ampex machines.
(Editor's Note--I recently purchased a Nortronics version of this splicing block whose 45 and 60 degree saw cuts are equidistant from the ends.)
To splice with the Edi-Tall, press the tape into the channel with rocking/massaging motions until all crackling sounds cease. Slide or pull the tape as required until it just covers the 45-degree cutting slot. Use a single-edged
razor blade for cutting (available at any drug or hardware stores). (Not
only are single-edged blades infinitely safer than double-edged blades, but
they are more rigid; insertion into
the slot is much easier.)
You will dull the razor blade quickly and mar the splicing block if you fish for the slot with the blade held vertically. When lining the blade up with
the cutting slot, lay the blade down at a steep angle and drag it across the cutting slot, just as if you were using
your fingernail to count the teeth on a comb or crease a folded paper. Once
the slot has been found with the "trailing edge" of the blade, tip the blade up to the vertical position for cutting
Ideally, the blade should be sharp enough so that the tape can be cut by pressing the blade straight down through the tape, or by using a rocking motion along the length of the blade. Use of
a dull blade will require a sawing, bread-cutting motion which makes the cut less precise and causes flakes of the oxide to stray, increasing the likelihood of noise in the splice.
Unlike using a "Gibson Girl", the ends of the tape to be joined are prepared
one at a time; two tapes are never overlapped at the cutting slot. Each tape end is put into the channel, positioned so that its end covers the slot, cut
to an angle of 45 degrees with the razor blade, and removed so that the other tape end can be prepared. Remember to wipe the channel free of debris between, insertions of new tape. After they have been trimmed off at 45 degrees, both tape ends can be inserted into the block for splicing. From here on, the idea is to slide the tape ends towards each other until they meet, then a small section of 7/32 in. splicing tape is placed over the joint. When butting the two tape ends together, their point of contact will be easier to detect with a fingernail if you keep it well away from either cutting slot.
Insert the two tape ends into the block in preparation for butting them together. Cut a length of splicing tape and anchor it to a thumbnail or a spot near the end of the block. Slide the tape ends toward each other until you feel them collide; keep track of their point of contact. Gently center the piece of splicing tape over this point and press it down into the channel. Using the back of your fingernail, use rocking motions to massage the splicing tape into place.
Laying a piece of splicing tape in the groove is no easy task. Since the lips of the channel are narrower than the recording tape, you may line up the long edge of the splicing tape with one edge of the channel without fear of it reaching the edge of the recording tape. With the splicing tape tilted up on its side (not quite vertically), find the edge of the channel with the long edge
of the splicing tape--then lay the splicing tape down over the adjoining ends of the recording tape. On the other hand, you may have good luck with holding the splicing tape between a thumb and finger at one end and guiding it into position with the other hand making lining one edge up with the channel unnecessary.
Among the authors, opinions differ as to the appropriate length of splicing tape to be used. Sighted professionals consider 1-/2 inch to be standard, with the splicing tape ends cut at an angle. However, because it is difficult to line up the splicing tape with the channel, you may wish to start out with longer pieces (from 1 inch to 1-1/2 inch).
On the other hand, the alignment of a short piece of tape is less critical, and you may find it just as easy to adhere to the standard of 1/2 inch.
Manufacturers recommend that the tape be removed from the block by putting horizontal tension on the tape and pulling straight up with both hands. This will only work if the block is glued to a solid surface. (These blocks all come, with an adhesive backing for attaching them to the tape machine or to the work table.) Random wriggling motions may facilitate removal; the randomness of motion will prevent the tape from being nicked by the sharp edges of the channel. Because of the added stiffness of the splice, it is a good idea to slide the splice beyond the end of the block before removing the tape. Do not start at one end and peel the tape out of the block, since this will seriously damage the edges of the tape.
Somewhere between the why's and how's of splicing comes the where's. In most professional settings, the equipment and its orientation are permanent enough so that the relationship between the playback head and the splicing block is fixed. Here are methods for accurately determining the spot where you want to cut the tape and for transferring it to the block. (The perspective here is that of a right-handed person.)
First, examine the play-back head thoroughly. You will prevent deposits from your finger from clinging to the head's surface if you do so with the tape still in its path. In many cases, you can easily find the highest point on the curved surface of the head; this is where the "gap" is, the point of sound pick-up. The play-back head is magnetically shielded by being housed in a metal shield can. Occasionally, flanges of this can extend partially over the face of the head, making location of the gap more difficult to determine. For easy gap location, simply make some mark on the head structure adjacent to the head gap so that its position can be easily felt. You can verify the gap's location in making this mark by gently approaching the head with a dull screwdriver or other ferrous object while listening to the play-back system.
The exact position at which a cut is
to be made is found by manually "cuing up" the tape (rocking the reels to and fro or moving the tape by hand) while listening to the howls, bumps and grinds of the program material through the playback amplifier. Machines designed for editing have a way of defeating tape lifters and other transport functions to afford this kind of manipulation.
(A very good machine for editing is the Sony Model TC1O5 with its tape lifters removed, as was done by APR.)
Once the exact position for editing
has been found, firmly anchor the tape
to the center of the head with your left thumbnail; unreel enough tape from the right side so you can hold it in your right hand. Gently bend the tape over your left thumbnail. You now have a "cradle" of tape whose center is anchored to the center of the head.
Slowly pull cradle and thumbnail as a unit away from the head and, at the first chance you get, substitute your left index finger for the head. You still have your cradle, and you can hold its center securely enough with your thumb and finger to permit release of the tape by your right hand. The right hand can now take a razor blade and cut right at the center of the cradle, using your thumbnail as a guide. (Watch out! A short thumbnail and a sharp blade may be hazardous to your health. You may prefer to use precision scissors as listed in the Tools Section at the end of this article.) This cut will be surprisingly straight.
Now, you can put the tape
into the splicing block and position the end so that it just covers the 45-degree cutting slot. The little bit of tape
you sacrifice in tailoring the splice will not damage the sound noticeably,
if at all. After all, most editing will not be done at speeds slower than 7-1/2 i.p.s. where a whole inch covers just under 1/7 second. On the other hand, you may develop consistency in predicting the amount of tape to be sacrificed, in which case you can give yourself a little leeway in making the initial rough cut. For example, if you learn to consistently sacrifice 5/16 in. at the editing block, you could then cut the tape alongside the play-back head whose width is 5/8 in., and you could do this rough cut without removing the tape from the machine.
Other than the above detailed set of instructions, there are many ways of making the rough cut. Some of the authors cut the tape to either side of the head with scissors. Some blind tape editors do as their sighted-counterparts do-mark the tape with a grease pencil; if you do this heavy enough, the mark can
be felt after bringing the tape back to the editing block. Whatever method you choose, consistency is the over-riding criterion of success; results you get must be repeatable.
If syllables or other minute sounds must be excised and put back, they may be spliced on to longer pieces of tape or leader tape for safe storage. The constancy of the cutting angle in modern splicing equipment ensures clean reassembly.
Any instruments used in the manipulation of recording tape should be demagnetized periodically. Not only should this be done before editing, but your screwdriver should be demagnetized before using it to align tape heads.
If this procedure is not carried out, you stand a good chance of "recording" your tools.
Demagnetization of a tool can be done with a bulk tape eraser. With the tool held well away from it, turn the eraser on--then bring the tool into the strong alternating magnetic field. Make a couple of circular motions with the tool, then slowly remove it to a safe distance
(about 3 feet) and turn the eraser off.
Where possible, tape-editing tools
are made of non-magnetic material; splicing blocks are made of aluminum
or brass. Stainless steel tools--when you can find them--are very handy because they are essentially non-magnetic (stainless steel blades tend not to hold an edge very well).
the scissors you get should be thin enough to fit on either side of your play-back head. On the other hand, your cuts will be consistently straighter if the thickness of the blades is not markedly tapered. A small pair whose blades have a fairly constant thickness is preferable.
High-quality scissors of various shapes can be gotten from cutlery suppliers (check the Yellow Pages in your phone book). A wide variety of small scissors is used in medicine; you may be able to filch a pair from your family doctor. Some of these are stainless steel. I have run across such things as dissecting scissors and locking forceps in the "lab supplies" section of
now that the X-Edit Company has assumed the production of the "Edi-Tall", it has now become "Edit-All". However, these must still be the authentic item, since X-Edit offers Mr. Joel Tall's booklet on tape editing. The Edit-All block sells for about $20.00. Nortronics makes an identical unit, the QM311, for $25.00.
Everybody makes the stuff; some are a lot worse than others.
Your Editor finds that Radio Shack's version exhibits all the properties warned against in this article. The splicing tape most often used is made by 3M, Scotch 41-7/32-66--(7/32 in. wide)-- and 41-1/2-66--(1/2 in. wide). Nortronics makes a 1/2 in. tape, QM501.
Two grades of the original Robins "Gibson Girl" are recommended. There is a $160.00 "Professional Gibson Girl", but it's catalogue description makes such a strong point about the "Gibson Girl" trimming concept that one is left with the impression that its use on quarter-track tapes would not be appropriate. These products and their Radio Shack equivalents are listed below:
- Professional Gibson Girl, 26-048-$160.00 (perhaps not suitable for home use).
- Plastic version of the Gibson Girl, 26-038--$10.50 (because of its structure, remnants of the splicing tape are hard
to clear away under the cutting arm. However, because the tape guides are moulded and not stamped, they are more precision than those on the deluxe unit.)
- Deluxe Gibson Girl, 26-045--$15.00 (because of its configuration, this unit has more room for your fingers under the cutting arm.)
- Cassette Gibson Girl, 26-043--$10.50 (this is a modified version of the plastic 26-038, its tape guides accommodate 1/8 in. recording tape.)
- Deluxe Replacement Parts Kit, 26-047-blades and cutting pad (although not stated specifically, I believe this repair kit will work with the plastic version 26-038.)
- Replacement Parts Kit for Cassette Version, 26-044--contains blades and cutting pad for cassette version 26-043.
- Radio Shack (Version of the Cassette Gibson Girl) 44-214--$6.50. (Editor's Note--My Radio Shack Catalogue no longer lists their version of the quarter-inch Gibson Girl, but it wouldn't hurt to ask. In addition, I see no listing for a parts replacement kit, although I'm sure the Robins 26-044 will fit.)
- Audio Distributors (handle such manufacturers as 3M,
major Nortronics, and X-Edit), 2342 South Division Avenue, Grand Rapids, MI 49507, Phone:
- Robins Industries Corporation (I was unable to find a central distributor for these people, but a phone call will get you a distributor in your area),
75 Austin Boulevard, Commack, NY 11725, Phone: (516) 543-5200.
Abstract--This discussion specifically describes the techniques that the Editor uses to repair the regular sized "Philips cassettes". In addition, appropriate tools and materials are listed. However, because of their basic design (without flanges, the little tape reels are left to rub against the housing), wrinkles and splices in the tape may cause future trouble in repaired units. Therefore, I recommend that once the material has been retrieved, it should be copied onto a new cassette and the old one discarded.
You will have need for the following:
- Gibson Girl type splicer Robins 26-043, Radio Shack 44-214.
- A repair cassette such as the Radio Shack 44-626 (while these repair units generally cost over a dollar, you can often buy cheaper screw-type units such as the Maxel C30 duplicator cassettes sold by IRTI for 85 cents).
- Small Phillips screwdriver (a small standard screwdriver is needed for BASF tapes which have slotted screws).
- Sharp scissors.
- Substantial uninterrupted table space (3 feet wide by 2 feet deep).
A table without moulding on the edge (without a lip) is preferable, since sliding the tape reels off the edge is the safest way to pick them up.
- Two flat boxes--one for tools and the other for loose parts--this will keep you from jostling the cassette parts when looking for these items.
- Clean, dry hands (oily hands stick to the tape).
- Nothin' to lose, lots o' time, and the patience of Job.
Because of the fabrication cost, cassettes which are screwed together are rare. Most of them are cemented together.
Opening the glued units is fatal to their structural integrity, since the plastic studs which hold them together must be fractured. For this reason, repair cassettes which are screwed together are available to which the tape can be transferred.
The cemented units are easy to pry apart with a screwdriver inserted into the record "knockouts" on the rear edge of the cassettes. Once a crack has been started (hopefully between the two halves), the screwdriver can be worked around the edges. Resist the temptation to penetrate the crack very deeply in your destructive zeal--you don't want to come in contact with one of the tape reels.
Components of cassettes are almost standard enough to be interchangeable. You may choose to keep such items as the pressure pad assembly and the pulleys.
(We will have a use for the Teflon liners in "Soldering, Part VI, Multi-pin Connectors".)
Inventory of Parts
The cassette contains the following loose items, none of which can you afford to lose:
- Two very thin sheets (liners)-- Teflon in the good ones and polyethylene for the low-grade units.
- Two small pulleys with pins
for bearings, one for each front corner of the cassette. Often, they have a preferred orientation on their pin. For example, some of them have a slightly protruding hub on the top side,
with their bottom hub being inset.
- A large metal plate, the head
shield cap, which shields the head from stray magnetic fields (to cut down hum pick-up) and which also supports the pressure pad.
- A pressure pad glued to a thin
slip of spring steel having fins which straddle matching fins on the head shield.
Disassembly and Reassembly
In disassembling reusable units (screwed together units, including repair cassettes), take careful note of the parts whose position is critical. For example, you will find that the liners have a surprising variety of subtle differences--a beveled notch here or a hole there. Noting these features in the beginning will help you if any questions come up during reassembly.
A repair cassette contains extra reel hubs with a section of leader tape between them. You may not need to replace a reel hub, in which case these can be
discarded--I have a whole drawer full of them.
The pressure pad and head shield cap constitute an assembly which is easily jostled out of position. Until it is held in position by closing both halves of the housing, the pressure pad spring is merely standing on edge leaning
up against the fins of the shield cap. These items are very hard to rearrange if the tape is still in its path; the tape should be removed if they need reassembling.
It is said that one can put the pad spring in place with tweezers. Balderdash! The best way--in fact the only way for me--is to drop it into place, and this is easier than it sounds.
The shield cap stands up vertically at the back of the head chamber. Its sides extend forward, and in the center of each side is a small projection. These projections are the "fins"
against which the pad spring is supported.
To reorient the pressure pad, straddle the shield cap with the pad spring and temporarily let the bottom edge of the spring rest on top of its intended support fins. By gently leaving the pad with an upward/backward motion, you will let it drop down in front of its support fins.
An alternative method is to remove both items, straddle the shield cap's fins with the pad spring as intended, and place them back into the head chamber as a unit.
With your thumb, check to see that the pressure pad is centered in the front window of the head chamber. When feeling the pad, make sure you do not lean it forward; keep in mind that it is
just leaning back against the fins on
the shield cap. Tipping it forward accidentally will cause the spring to slip down under the support fins, and the whole procedure of installing this assembly will have to be repeated. If anything, when you feel this pad, pressure must be applied back and downward so as to lean it back against the shield cap.
All procedures for threading the tape will be discussed shortly, but a description of its course through the cartridge is appropriate here. The tape actually goes on the outside of a plastic post
(probably an anti-skewing device, it defies my sense of logic), then around a pulley. From here on it makes a straight path across the front of the cassette, after which it goes round the other pulley and finally around the outside of the plastic post.
Finally, there are tricks which come in handy when putting the two halves of the cassette together:
- If the liner has been smoothed
out against the top half, vacuum tension will hold it in position long enough for reassembly.
- In order not to catch and pinch
the tape between the front lips of the housing, first match up the front corners with the top half tipped up at an angle (30-degree or 45-degree).
- Before inserting the screws, hold the cassette together and try turning one of the reels with a Braille stylus. If they turn stiffly, one of the reels may not be exactly in place, and jostling them one at a time with the stylus will fix this problem. If the tape cannot be moved at all, it has been caught between the two halves. You can always lift away the top half and turn the reels by hand in order to better assess the problem.
Handling and Repairing the Tape
The tape in a cassette is 1/8 in.
wide and very thin (the tape in a C30 is 1.5 mil., 0.0015 in. thick). Don't be discouraged, the following is a longwinded discussion of techniques as to how you can keep track of the wispy stuff.
Much of the frustration comes from the fact that the little reels of tape have no flanges. Very often, wraps of tape will "loop off" the top and/or bottom of a reel while you are working on it.
The instructions which come with repair" cassettes recommend that you place a strip of splicing tape across the reels to act as makeshift flanges. With this procedure, you do run the risk of having your "flanges" stick together, or having the tape get caught on one of them. If you use this method, make sure that any splicing tape which extends past the edge of a reel has been folded over so as to be harmless--and take this precaution before you lay it across the reel.
The reels can be picked up and handled without the tape slipping off as long
as there is tension on the tape. As
soon as the tape becomes slack, it will falloff in glorious ringlets (especially if the reel is held flat without a finger at the edge to support the outer wraps of tape).
In unrolling and re-rolling the tape,
I prefer to keep the reel on edge. I monitor the tape as it is coming off and going back on with a thumb and finger while using other fingers to cradle the
edges of the reel and to serve as brakes. I keep a slight even tension on the tape by lightly clamping it under or between the third and fourth fingers of the hand whose thumb and first finger monitor the edges of the tape.
The tape can best be felt while it is under tension. For example, a tape which is ready to go back into the cassette can be assessed for twists only if the reels are held so that the tape is taut between them. The quality of the splice can best be judged by running the edges between a thumb and finger while the tape is held in tension. Also, the lips have very good tactile acuity for exploring features of the tape while it
is held in tension between your two hands.
The best way to get a reel off the table and into your fingers is by sliding it off the edge. The edge of the table is handy is handy in other ways as well. If you are re-rolling tape onto one reel while it is still connected to the other, do so with your reel held below the surface of the table. This will prevent you
from unwittingly lifting loop after loop off the reel which is still lying on the table. Twists can be taken out of a
tape by sliding the emptier of the two reels off the edge of the table and flopping it over and over in your hand; the reel being manipulated can at any time
be slipped back onto the edge.
Since the sides of the reels rub against the top and bottom of the housing, unevenness in the winding of a tape cannot be tolerated. Crooked splices or wrinkles in the tape will start an uneven trend during playback, causing the take-up reel to bind
and bringing you more trouble. It is
with much experience and sound reasoning that I urge you to freely sacrifice slightly damaged tape when making repairs. Unroll as much as you need to until the tape feels smooth and is once again full width. In addition, check the edges of the reels during unrolling so as not to miss potential problems buried under several wraps. I quite often discard several feet.
Since the tape in cassettes is wrapped
with the magnetic material on the outside, splicing is done on the inside surface, as opposed to how it is done on open-reel tapes. In loading the splicer, I slide each reel off the edge of the
table, find the plastic side of the tape, secure and trim this end in the splicer, and then go after the other reel. Don't worry about full-turn twists just yet, these can be gotten out after splicing has been accomplished. (Half-turn
twists are a no-no--these come about
when you splice the plastic side of one tape to the magnetic side of the other.)
Splicing is done exactly as described in the previous article under the section "Automatic Splicers". However, making sure that these thin tape ends overlap properly in the splicer is troublesome. I let the free end loop over the opposite securing arm where I can feel it, and then trim the ends one at a time.
After the splice has been made, lift it out, hold the tape in tension between your two hands and examine the splice with your lips or with the thumb and forefinger. The most important consideration is that its edges be straight and not jagged.
Slide the fuller of the two reels off the table and carefully wind it up until the reel on the table moves, indicating that much of the slack has been taken out between them. Put the full reel back on the table. Take a reel in each hand and put the tape in tension.
Gently roll up one or both of them so that they approach each other; when they are less than three or four inches apart, you will be able to feel twists in the tape by following its edge with your forefingers. Maintaining tension on the tape, bring both reels toward you until you get the smaller reel off the edge. Using a trial and error process, flip this reel in complete somersaults until the twists are gone.
You now need to place the fuller of the tape reels into the bottom half of the cassette shell. After many unsuccessful attempts at tipping the reel up and over the edge, I have reached the conclusion that the easiest way is to bring both reels off the table's edge and on to your fingers with the thumbs being used to guide the tape as it tangentially emerges from the circumference of the reels. Maintaining tension between them, I ease the full reel down into the shell, and hold the emptier one as close to the table as I can; the tape should be leaving the cassette shell at the near front corner.
With a watchful thumb or finger keeping the tape from looping off the full reel and with tension always being maintained, swing the other reel around so as to lay the tape in its intended path, while using stray fingers of either hand as feedback to guide it correctly.
Once the tape is in place, gently turn the two reels so as to keep tension on
it as you examine your handiwork. A common problem to look for is that the tape may be running along the outside of the structures along the front lip; gently massage it upward with your thumbs until it disappears behind these various structures (avoid that pressure pad).
If at any time something goes wrong, abort the mission, take the reels out and try again. You are better folks than I am if you can correct a looped over tape or jockey with the pressure pad with the tape installed.
The final stages of assembly are repeated here: smooth out the liner in the top half, bring its front corners up to match those on the bottom half (doing this with the back of the top tipped up to an angle of at least 30 degrees). Lay
the top down and assure yourself that it fits well against the bottom--there should be no cracks or wobbliness. Holding the two halves together, try turning one of the reels by twiddling it around with a stylus; it should pull
the tape along freely.
Occasionally, you will find a cassette whose top half contains almost all of the structure of the front edge. While these make threading of the tape very easy, the tape is susceptible to being pinched when the two halves are mated. When putting them together, I have had some success in dragging the top along the table (holding it at a
very steep angle), then easing it up on
to the front edge of the lower half.
BASF cassettes have pivoted arms
along which the tape is threaded--one arm for each reel. While they pose no threat to threading the tape, they are very much in the way when placing the reels in position, especially the full reel. You may wish to remove the arm next to the full reel with the intent of replacing it after the tape is in place.
Occasionally, tape can be fixed without taking the cassette shell apart, especially if all that is wrong is a half-turn twist somewhere along it. Probing in the head window to extract
the tape is very risky; you can easily dislodge the pressure pad in this manner. You can safely retrieve the tape with
a stylus through one of the end windows. I very often extract the tape by putting my mouth up to the desired window and sucking it out.
A half-turn twist can be found and corrected by looping the tape around a finger and turning one of the reel hubs so as to pull the tape along; turn the
hub with a pencil or with a Braille stylus. Once the twist passes over your finger, orient the tape correctly and use your thumb and finger to guide it back into the cassette as you turn the tape in the other direction. Do this until it is evident that the other end of the twist has been straightened out.
You can section out damaged tape by pulling it out through one of the windows, cutting it and splicing it as discussed above. However, it is important to note the orientation of the tape when loading the splicer, otherwise you may end up with a full-turn twist in the tape which may mean that the cassette shell will have to be dissected.
Before I practised this art, cassettes were very frustrating to me since I could do absolutely nothing once they had tangled. Even at my worst in repairing them, I do take comfort from the fact that sometimes the material can
be salvaged. I realize that the above procedures sound frightening, but my impression is that they require less dexterity than sewing; I can tangle more thread in mending a seam than the amount of tape involved in a year's subscription to SKTF.
SOLDERING, Part V, RCA and Motorola Plugs
By the late 1930's, there were consistent needs in consumer products for low-cost "shielded" (coaxial) connectors for use at audio and low radio frequencies. Two such connectors were developed to address these needs--the "RCA phono plug" (now the standard for interconnecting hi-fi components), and the "Motorola plug" (now the standard for automotive receiving antennas). (Note that in traditional terminology, a distinction is drawn between" "shielded" and "coaxial" cables and plugs in discussions of audio and r.f. signal lines, respectively. Since single-conductor shielded cables such as those used on these plugs are coaxial, the distinction will not be made in this article.)
These two connectors are very similar in concept. Both have a tubular center-conductor pin into which the "hot lead" is soldered. Both have a four-segment shield shell, to which the "cold connection" is made, which snugly fits a matching shell on the socket. The shell of the RCA plug is a bell-shaped affair which surrounds the shell of its socket; the shell of the Motorola plug is a sleeve-like structure surrounding the cable which fits into the shell of its matching socket. Having four segments and being made of springy metal (usually a hard brass plated with tin), these plugs can easily be adjusted to tightly fit their respective sockets, thus eliminating the need for close-tolerance machining in their fabrication ("stamping" and "extruding" are the only fabrication processes necessary).
Noting the principles of soldering as stated in Part I. of this series (summarized at the beginning of Part II., Winter, 1981), rare is the soldering job which requires as many wholesale violations of the rules as must be done in installing these connectors. The procedures for installing the plugs along with the rules to be broken are listed below:
- "To solder the tubular pin, pass the lead through the pin and secure the connector in a vice so that the pin points upwards; heat the side of the pin while feeding solder straight down into it."
- Efficient heat transfer only occurs when there is a continuity of alloys between the iron and the work, i.e., the iron should be in a solution of solder along with all the work pieces. This cannot happen with the iron on the outside of the pin and the soldering going on inside the pin. Furthermore, in order for all pieces of the work to heat up together, they must be in firm physical contact. Since the wire is usually much smaller than the inner diameter of the pin, firm contact is unlikely.
- "On the Motorola plug, the cable shield is folded back against the outer sheath so as to contact the inside of the staves of the connector shell; after insertion, all four segments of the shell are soldered to the braid."
- As with the center conductor pin, the iron is used to heat up the outside of the plug while soldering takes place inside the shell. A solution of solder cannot be established between the iron and the work, since spillage of solder onto the outside of the shell would prevent its fitting into the socket.
- "On the RCA plug, the cable shield is to be folded over the top of the bell-shaped shell and soldered to it."
Where possible, all components of the work piece should be in contact with the iron so as to heat up simultaneously. Where this is not possible, the iron should at least be in contact with the item of largest heat capacity, the largest piece of metal. Unfortunately, in the case of the RCA plug, the iron will be resting on the thin braid wires and not
on the metal shell of the plug. By the time the shell is brought up to soldering temperature, the braid wires will have been heated for a considerable length of time, and they often conduct so much of this heat to the cable that the center insulator becomes severely damaged.
The points discussed in this section describe how we can cheat the laws of physics with "tricks of the trade".
Soldering Tubular Pins
Because these pins fit into spring contacts in their socket, it is imperative that no spillage be allowed to change their size and shape, which would damage any socket receiving them. One thing in our favor is that these pins are often plated on the outside with a metal less soluble in solder than the base metal (they are often plated with cadmium). Therefore, solder is less likely to stick to the outside than it is to the inside. When going into solution, solder loves to "wick" along, around, and into highly-soluble materials via "capillary action". Therefore, we can expect solder to guide itself in the direction of soluble surfaces; it will gladly flow into and around the inside surface of the pin as soon as the necessary soldering temperature has been reached, whereas it will just tend to "bead" on the outside of the pin.
(If solder is melted directly under the iron, it will alloy with some of the plating.)
The diameter of the lead is very often much smaller than the inside diameter of the pin; being very loose in the pin, it may at times not be in direct contact with the inside of the pin. As the pin fills with solder, it becomes a sort of "secondary soldering iron"; it is intended that heat be conducted from the pin to the lead via the molten solder. However, two roadblocks can foil this plan. First, you may not be able to spill enough solder into the pin to make a good conductive puddle, or by the time you do so, some of this solder may have melted through the cable insulation to cause a short behind the plug. Second, the flux may be used up before the materials inside the pin have been deoxidized to any significant depth. By generously pre-tinning the lead and by inserting a piece of thin solder into the pin along with the lead, these problems are minimized.
With the above principles in mind, the following three methods can be used to solder a wire into a tubular pin:
- A tinned lead is prepared whose length is just short of reaching the end of the pin. If the lead diameter permits, slip a piece of thin solder into the pin alongside this lead and cut it off at the end of the pin. Clamp the connector in a vice so that the pin points straight upward. Using fairly thick solder (perhaps .05 in. diameter), vertically orient and position a straight piece of this solder directly on top of the hole in the pin, positioning your hand so that you can feed about 5/8 in. of it straight down into the pin. Being sure your iron is wiped free of residual solder (you don't want it to deposit solder onto the side of the pin), find the side of the pin with the iron and hold it there until the solder melts. Heat transfer will be best if your iron has a screwdriver or chisel tip; turn the iron until you feel its flat side rests squarely against the side of the pin (getting your feedback through the handle of the iron). Reciting perhaps 17 stanzas of your favorite verse, wait for the solder to melt--then feed it straight down into the pin. If anything goes wrong--if you cut the solder in half with the iron while looking for the pin, or if you lose the pin while feeding the solder--let the project cool, clear away any droplets from around the work and try again.
- Prepare a long section of well-tinned lead whose length is sufficient
to protrude about 3/4 in. beyond the end of the pin. This time, it is essential that a piece of thin solder be inserted into the pin alongside the lead, primarily to provide fresh flux for cleaning the pin's inner surface. You needn't cut the solder off as it emerges from
the end of the pin; you can use this
same solder in making the eventual connection. Clamp the connector in a vice with the pin straight upward. Hold the solder off to one side in preparation
for feeding it to the protruding wire, not to the pin with the iron, find the point at which the wire emerges from the pin; rest the iron so that it contacts both the wire and the end of the pin.
The solder in your hand will quickly be disconnected from the pin, at which point you should fish for the wire
above the iron. Feed perhaps an inch of solder to the wire, taking care to
avoid the pin. The theory is that most of the solder will wick down the highly solder-soluble wire into the pin. For this scheme to work, plenty of fresh flux must be available to make the pin's inner surface soluble, otherwise the solder will wick everywhere else. Of course, the wire must be small enough in diameter
to leave room for solder to run past it on its way into the pin.
- The connector pin can be pre-tinned--actually filled with solder--and the tinned conductor can then be run through the molten solder as the pin is reheated. Clamp the connector in a vice with the pin horizontal, or perhaps pointing slightly downward. Feed a straight piece of thick solder (0.05 in.) into the pin from the rear of the connector until it reaches the end of the pin; hold on to it behind the connector in preparation for feeding about an inch of it forward into the pin. Find the end of the pin with the iron and press the solder forward until it is melted by the iron, and proceed to fill the pin with solder. After withdrawing your piece of solder from the rear of the plug, slide the iron sideways off the pin and let the project cool.
Prepare a suitable length of well-tinned lead--its length is not critical. Fish for the rear entrance of the pin with this lead and prepare to drive it up to the hilt in the connector as you reheat the pin. Once again, find the end of the pin with the iron and wait for the solder to melt, which will be indicated by squeakiness and by the fact that the lead can be moved forward. Slide the lead in as far as it will go remove the iron and wait for the solder to solidify without jarring the cable. If the lead is longer than the pin, you will feel it run into the iron--in which case, follow it out with the iron, letting the iron be pushed away from the end of the pin.
This last method may be more difficult with Motorola plugs, because the shell is so long that the pin is difficult to find with the center lead. With the continuity tester connected between the hot lead at the other end of the cable and the connector pin, you can verify having hit the solidly-filled pin with the lead. The pin rarely stays completely filled when being tinned, since some of the solder is bound to run out the forward end. Therefore, you may feel a depression at the rear of the pin with the lead, and you may even achieve partial insertion before the pin is reheated.
Beads and icicles of stray solder can be removed with a clean iron, a knife, or a file. If the pin's plating did not take the solder, spillage can easily be picked off with a fingernail. The important thing is that the pin be round and of an appropriate diameter for its matching socket.
Spillage of solder around the base of the pin, the application of too much solder, or over-heating of the project can all cause short circuiting of the plug and/or cable. After each and every step, it is wise to check for shorts between the pin and the shell, and between the pin and the cable shield.
Installing Motorola Plugs
In principle, braid is folded back over the outer sheath and tinned before inserting the cable into the connector; this braid is to be soldered to the four staves of the shell at the rear of the connector. Critical dimensions are listed below:
- The tubular pin is about 1.1/16 in. in length; the center lead should be prepared accordingly.
- In order for the shell to reach the full insertion of 5/8 in. into the socket, its four springy staves should be free to expand against the sides of the socket for this distance, making it necessary to solder the braid behind this point. Allowing 1/8 in. for the insulator to which the tubular pin is mounted, there should be a spacing of 1/2 in. between the entrance of the pin and the point at which the braid is soldered. In other words, the center insulator should extend at least one half inch beyond the folded-back braid.
- This connector's shell is best suited for a braid whose outside diameter is about 5/16 in. RG59/U with
its braid folded back over the outer sheath is about this size, while braid folded back on RG58/U is too small.
Where necessary, masking tape or other non-contaminating material can be wrapped
around the outer sheath of smaller cable so that the braid can be formed around something of appropriate size. (Actually, it is a good idea to wrap a layer of this tape around the outer sheath of any cable, even RG59/U, to keep the intense heat of tinning and soldering from melting the plastic, thus contaminating the braid and making it unsolderable.)
Preparing and Tinning Braid
Of course in preparing the cable, a decision will have to be made as to which method of soldering the tubular pin you intend to use, since the appropriate length of exposed center conductor varies among the three alternative methods discussed earlier. Behind the exposed center lead, the following procedures should be carried out:
- Strip off about 5/8 in. of outer sheath--after the braid has been folded back, this will give you just over one half inch of center insulator to act as a spacer inside the plug.
- Before folding the braid back over the outer sheath, wrap paper or masking tape around the cable at the end of the sheath to protect it from the intense heat of tinning and soldering.
If the cable diameter is smaller than about 1/4 in., wrap enough tape around it to bring it up to size.
- Fold the braid back over the sheath and smooth it out in preparation for tinning. You will probably have to unbraid about half of it to accomplish this; do so carefully with a Braille stylus or other instrument which is thin but not sharp. Sometimes, braidwires get rather sparse as they are expanded over the outside of the cable; in this case, twist the cable between your fingers and wrap them around the sheath near its forward end.
- Wrap a couple of turns of thin solder around the braid nearest the forward end, just over the end of the sheath. Gently wipe the iron over the circumference of the braid's forward end; tinning will not take long, since the expanded braid has very low heat capacity (you may wish to wrap the center insulator in a bit of masking tape to prevent it from being damaged by the
iron when you miss the braid.) Let the project cool and survey the damage.
An occasional lump of solder will not
hurt anything, since these connectors do not need a "precision fit" between the braid and the shell. Any loose braidwires behind the tinning job can simply
be folded up near the front of the braid and forgotten about.
Pre-Tinning the Motorola Plug
Tinning the inside of the shell is an essential part of the installation of the
plug. There is no other efficient way
of getting solder and fresh flux inside the shell and on to the shield connection.
Tinning the inside of the shell of a Motorola plug is good fun--it is one soldering job during which you cannot get lost. Clamp the tubular pin horizontally in a vice and turn the plug so that the stave to be tinned is at the bottom. Slip a piece of thin solder through a crack near the top of the shell in preparation for feeding about an inch of it down on to the bottom stave. Insert the tip of the iron into the shell and rest it on the bottom stave near the open end. Feed solder to this stave just ahead of the tip of the iron, then slowly withdraw the iron from the shell. Turn the plug so that this can be done to all four segments of the shell.
Soldering the Shield of the Motorola Plug
Slip the tinned plug over the prepared cable and solder the tubular pin; this will help keep the cable in position. (You can assure firm contact between the segments of the shell and the braid by bending the staves inward so as to tightly fit the cable. They can be bowed out again if the plug fits loosely in its socket.) Now clamp the tubular pin horizontally in a vice and reheat the staves one at a time. As the solder melts under the stave, you may feel it give a little under the iron--but more importantly, you will feel a rise in the temperature of the cable behind the plug. After doing this to all four segments of the shell, let the project cool. (You need not do all four segments at once; you can let the plug cool after each phase if you wish to.)
The connector should not rotate freely with respect to the cable; even with the center conductor soldered, there will be considerable freedom of motion if the braid has not adhered to the inside of the shell. Furthermore, you should not be able to lift individual staves away from the cable.
Reheating parts of the plug can be
done to correct problems unearthed during testing. If reheating fails to attach segments of the shell to the cable,
there is a secret weapon we have to assure eventual soldering of the shell. Lay a piece of thick solder in a crack between two staves and place the iron on top of it just over the braid beneath. This will get some action; you can have fun filing the plug back down to size and polishing it off with emery cloth after this drastic measure has been taken.
Installing RCA Phono Plugs
In principle, the braid is flared out so that the plug can be slipped onto the center conductor and soldered, then the braid is closed over the rear of the plug (about the top third of the "bell") and soldered there. Critical dimensions are listed. below:
- The length of the tubular pin varies considerably--from as short as 1/2 in. to a length of one inch. Older units came in two sizes, long and short. A nominal 5/8 in. will serve as a practical estimate.
- There should be at least 3/16 in. of insulation between the flared-out braid and the exposed center conductor. The presence of this insulation is absolutely necessary, since this portion of the center lead passes through a small opening in the rear of the bell-shaped shell behind the tubular pin.
- The flared-out braid wires only need to be about 3/8 in. long, since soldering is done on the rear portion of the shell and not along the
four segments. However, I usually trim the braid wires 1/2 in. with the idea that they can be trimmed or filed off the connector later.
Tinning the RCA Plug
A fair sized puddle should be created at the back of the shell; when the braid is pressed against the connector with the iron, it will sink into this puddle and soak up the molten solder like a gauze. I tin the plug with its tubular pin held horizontally in a vice. I touch the shell with the iron and the solder in two or three places around the circumference of the shell (do this toward the rear and try to avoid the segmented section). After the unit has cooled, I check for bare metal with a fingernail--those portions wet with solder will be very smooth and gummy with flux. I usually find a spot which needs redoing, whereupon I turn the plug to make this point accessible and go after it again. Lumps of solder are not very important at this stage, but if they offend you, wipe them off with the iron after you have
stripped its tip free of excess solder
on your cleaning sponge.
Soldering the Shell of the RCA Plug--Solder the tubular pin to the center lead, making sure that the plug has
been pressed back firmly against the flared-out braid. (If the cable is large and stiff, you can hold it vertically in the vice while soldering the pin. If the cable is small or very flexible, hold the connector in the vice while making sure the cable is being pushed up snugly underneath.)
Turn the connector over and clamp its tubular pin in the vice with the segments of the shell resting on top of the vice jaws. Arrange some way of holding the cable straight up from the connector. Having the cable held vertically is very important, since letting it droop sideways will bring the center insulator of the cable firmly up against the rear entrance of the shell; as soon as the shell is heated, it will cut through the insulator and short out the cable. Finally, firmly press and smooth the braid down over the shell. You may
even wish to tie the braid in place with a piece of thin wire--this wire can be smoothed down with a file afterwards.
With the iron in one hand and the solder in the other, solder the braid in a few places around the shell. You will not need to apply much solder, since what you are mostly doing is providing the braid wires with fresh flux. You will only need to do this in four or five places around the shell, and you can take as long between solderings as you wish. You may even wish to turn the connector in the vice in order to conveniently reach all sides. If your vice has metal jaws, you can use them
as a landmark by which you can first find the connector shell and then hop
up to the upper rim of its bell-shaped structure. In doing so, be careful not to jostle the braid wires out of position.
After the project has cooled, check
to see that adhesion has been accomplished on all sides. Any individual loose braid wires can be "tacked" down with the iron, most likely without applying additional solder.
With wire cutters, trim ragged edges
of braid off the plug and file the plug until it is round and smooth. Do not trim or file away any material at the back of the shell, just around the sides.
Alternative Methods for Attaching the Basic Connectors
Now that you know the "right way" to attach these plugs, perhaps you'd be interested in how most of us do it. Although not as elegant, the braid is often attached by gathering it into a "pigtail" and soldering it to the side of the shell--soldering is only done in one spot. Furthermore, since they are gathered together, individual braid wires are less likely to sever when the cable is flexed. This trick can be used on Motorola connectors by bringing the "pigtail" out the rear of the plug and lapping it over the end of one of the staves. (It should be noted here that this is how such connectors are attached to unshielded 2-wire cables, such as speaker lines and other non-coaxial applications.) A detailed example
using an RCA plug is given below:
Generously tin the "pigtail" and one spot on the rim of the plug's shell. Bend the "pigtail" so that it curves around the upper rim of the shell, covering about 1/4 of the circumference. Grab the end of the "pigtail" in locking forceps and hold it in position while bringing the iron into contact with both items. Watch for the squeakiness of solder-wet metals and for a rise in temperature of the cable. Remove the iron and don't move. If it didn't stick, wrap thin solder (0.03 in.) around the "pigtail" where it is to contact the
plug and try again.
There are two accepted ways of getting a "pigtail" of braid:
- For cables whose center conductor does not bend easily, the braid can be unwoven--simply combed out with a non-pointed instrument such as a Braille stylus. Once the braid wires are separated, they can be gathered together and twisted into a bundle.
- With careful surgery, the center conductor can be extracted from the braid at the end of the outer sheath, thus giving you a braided pigtail. Remove a generous length of the cable's outer sheath. Surrounding the braid with three fingers, massage it backward until there is a little "balloon" of
it right against the end of the outer sheath. Sharply double the cable over at this point (at the balloon of braid). With a Braille stylus, gradually work a hole in the braid at the outside of
this bend. Gently shift all the braid wires over to the inside of the bend, exposing the doubled-over center conductor. Being careful to miss all the braid wires, slip your stylus through the loop of center conductor and ease
it out of its knitted sleeve of braid. Afterward, look for whiskers indicating severed braid wires at the base of the center conductor; get hold of them and simply pull these wires out and discard them. Finally, massage and pull the braid out into a nice thin pigtail.
Alternative Varieties of These Connectors
A wide variety of these plugs are available, especially in the case of RCA phono units. Your Editor's favorite variations will be listed here. In addition, although perhaps not honestly classifiable as "alternative designs", certain critical variations in the shape of basic RCA plugs will be discussed.
H.H. Smith makes a unit (12WJ) which includes soldering tabs at the rear end of two of the staves. Although I am not absolutely sure of their intended use, it appears that they are to be soldered to the braid without its being folded back over the cable's outer sheath. In any case, the tabs can be adjusted to accommodate any size of cable, or they can be treated as solder lugs to which a pigtail is attached. These tabs can be cut off and the plug treated as described earlier.
Basic RCA Plug Differences
Although I have used plugs without this feature, very often the bell-shaped shell of the plugs you buy will have a "double cup", that is, behind the large-diameter segmented section of the shell is a slightly smaller-diameter section (also having straight sides), and the braid can be tied into position around this portion
of the shell with a piece of wire.
(Actually, this small-diameter section is used to hold the phenolic insulator of the tubular pin.) As far as ease of soldering is concerned, I would not reject plugs which are not so shaped.
There are mean/nasty self-destructive plugs having sharp edges at the rear entrance of the shell which will damage the cable after it has been attached.
A notable example is the Switchcraft 3501M, whose shell includes a sharp-edged, flared-out portion which they use for mounting this plug on various adaptors and cable clamps. The sharp edges at the back of this plug will quickly sever the braid wires as the cable is flexed. It is important that you render any such connector toothless before approaching it with the cable. This can easily be done with a file.
RCA Plugs with Cable Clamps
The basic disadvantage of all the above units is that stresses on the cable are borne by its fragile wires and not by its protective outer sheath. Plugs are available with wrap-around cable clamps which grip the outside of the cable and keep it from severing the wires as it is flexed.
The Switchcraft 3501MC is a basic plug with an attached crimp-on clamp. This clamp has two stages, one for the outer sheath and one for the exposed braid
(although you will have less trouble if you use them both for the outer sheath and solder a pigtail of shield to the shell of the plug). Because it is not completely shielded, this unit is poorly suited for RF.
The Switchcraft 3502 is a very fancy unit with a screw-on cover. Its design has two major disadvantages. Its ground-connection device has no hole through which a shield pigtail can be inserted for soldering; the pigtail must be "tacked" on to the back of the cable clamp support. The other is that its tubular pin extends a full 3/16 in. into the connector housing, making short circuits between this pin and the cable shield all too likely. A fine hack saw can be used to cut this pin without affecting its structural integrity; this will separate the connection points and will give you room to fully grip the outer sheath in its clamp.
HINTS AND KINKS
This column is near and dear to your editor's heart, and I would like to see it become a regular feature. Its next appearance will occur after I have received three or four new items. To those of you whose ideas did not appear this time, I apologize--they have either gotten lost in my developing filing system or I did not understand the ingenuity of your suggestion. Please resubmit anything you feel should be included. Do not short-change your cleverness by sending me abbreviated explanations; be specific as to the
applications of your inventions and/or techniques.
Single-Cell Marking System for Quantifying Braille Dials
With dozens of braille dials around the lab, it becomes evident that a system for numbering major markings would be handy. Standard braille numbers become easily confuseable as they are rotated in space, especially without the presence of a number sign.
Roy E. Lockwood, W8CIL, of Charlevoix, MI, points out that use of the full cell reduces the confusion caused by rotating the characters, and he suggests using the following one-cell symbols to represent the numbers 1 through 10: "L" "th" "w" "ble" "er" "y" "p" "r" "v" "q" "and".
Numbers in the European Computer
Code are written without the number sign: the numerals 1 through 0 are generated by adding dot 3 to the basic dot combinations a through j as follows: "ch" "gh" "sh" "th" "wh" "ed" "er" "ou" "ow" "w".
Since they're your dials, go ahead and "roll your own" system. Thank you,
Negotiating Live Circuits on Printed Boards
John Lizza of Carle Place,
New York, recommends wrapping your hand in a plastic bag when feeling your way around live printed circuit boards. Occasionally, your effect on a circuit must be minimized while fishing around with test probes, and in some cases, a plastic bag could reduce the shock hazard.
Components are often shipped in antistatic bags which might be more appropriate for using this trick with CMOS circuits.
Thank you, John Lizza.
Tips on Soldering
Mike Bhagwandas, JA3TBW, of Kobe, Japan, recommends the following good ideas:
For soldering in hard-to-reach places among nests of wiring and among components of close proximity, a piece of thin fiberglass tubing can be used as
a guide. One end of the tubing is rested on the connection of interest, with the solder being fed through the tube. The tip of the iron can then
be slid down the tubing to the connection without fear of cutting the solder in half on the way.
(Editor's Note--I have been unable to find a source for small quantities of tubing; manufacturers apparently make such tubing to order rather than stock it. I am negotiating the purchase of 100 feet to be divided up and passed out in a future issue.)
I tried this scheme using 1/8 inch glass tubing which I filched from a chemistry lab in our associated hospital. The solder will gall against sharp edges of the glass unless the ends of the tubing are "fired" in the flame of a Bunsen burner or smoothed down by judicious use of emery cloth.
Holding the tube vertically, I support it between my ring and little fingers while feeding the solder with my thumb and first finger. Initial melting of the solder is facilitated by cutting the bottom end of the tube off at an angle, thus permitting the tip of the iron to touch the solder.
I was amazed at how much control in feeding the solder that this system affords and by how well this idea works. Given small diameter tubing, this may be just the thing for soldering components with short leads into printed boards.
In regard to attaching component leads to the pins of IC sockets, why not pre-tin the materials and then solder them together simply by reheating them once they are in contact with each other? In this way, you don't have to worry about feeding the solder, and you will be less likely to spill solder onto an adjacent terminal of the socket.
Since the socket pins are extremely small as compared to the leads being attached to them there should be enough solder on the lead alone to make the connection (this trick will surely work if you apply a small amount of flux to the socket pin).
Once the lead has been laid over against the pin, heat the connection. The solder will melt almost immediately; this will be indicated by the lead settling further over to the pin, by rapid heat transfer along the lead to its component, and by the squeakiness of solder-wet metals.
(Editor's Note-- "activated" flux is a good thing to have around.
It can also be used in preparing the inside of tubular pins; a pipe cleaner which has been dipped into the flux is inserted into the connector pin. Kester activated flux can be gotten by the pint from Marshall Industries (Kester No. 1544), 788 Palomar Ave., Sunnyvale, CA 94086, Phone: (408) 732-1100. The price of the flux is about $5.00, but be advised that Marshall Industries requires a $15.00 minimum. Thank you, Mike Bhagwandas.
BRAAGIS--The Blind Radio Amateur's
Auditory Gimmick Information Service (BRAAGIS)
has been set up by Mr. Peter H.E. Jones, G3DRE, as a central file to provide information about various auditory aids which are available or which could be duplicated. (The term "gimmick" is used here in the general sense including devices with talking or coded-tone readouts.) Please send any information (either construction details or sources from which "gimmicks" can be obtained) to BRAAGIS for inclusion on this central file.
A cassette library of the circuit data of selected auditory gimmicks (the circuits being verbally described) will be established for use by the amateur constructor. Further details will be provided on request.
Visually handicapped persons wishing to make use of or contribute information to BRAAGIS (which is operating on a volunteer basis in honor of the International Year of Disabled Persons) should send a cassette to:
Peter H. E. Jones, BEM G3DRE 68 Prospect Road
S17 4JB England
Phone: (0742) 46-9199.
VIBE--The Visually Impaired Builders and Experimentors (VIBE)
has been started in Pensacola, FL, by Nick Dotson and friends. It is comprised of blind experimentors, sighted teachers, and any persons wishing to be involved in an interchange
of ideas and techniques. As yet a Florida-based local group, it does have certain
key features vital to individual builders which are worth copying elsewhere. For example, VIBE has established accounts at
a few major suppliers. (As the individual builder soon discovers, required ordering minima and outright refusal on the part of some stores to sell to individuals can be fatal to many projects.) VIBE embodies
the principles of "clout behind numbers" and exploiting the benefits of collective understanding. Bravo, folks, from your editor, and when you get around to accepting dues-paying members from out of state, deal me in.
For further information, contact Nick Dotson, President, 1901 N. Baylen St., Pensacola, FL 32501.
Extra-Class Exam Tips
Gayle Sabonaitis, WAIOPN, of Worcester, MA, informs the editor that our "digital issue", SKTF, Summer 1981, was of help to her in passing her extra-class test. Glad to hear it, Gayle--I'll be sure to review that issue if I ever get up the courage to take said test.
- National Library Service, Library of Congress. In the March-April "Braille Book Review", the following two books appeared (page 69): The Radio Amateur's Handbook, 17th revised edition (RC16588, on cassettes), by Archie Frederick
Collins. (Apparently this is not the ol' "Radio Amateur's Handbook" by ARRL, which is into its 59th edition.)
- Complete Guide to Amateur Radio (RC26725, on cassette), by Joseph DuBovy.
- Courage Handi-Ham System of 3915 Golden Valley Road, Golden Valley, Minnesota 55422 has the following taped books available:
- ARRL Question and Answer Book for:
- Novice--four tapes
- Technical/General--four tapes
- Advanced--three tapes
- Extra--five tapes.
- ARRL 1981 License Manual
- General--11 tapes
- Advanced--10 tapes
- Extra--6 tapes
- CW Abbreviations and Q Signals--1 tape
- Rules and Regulations--1 tape
- Kantronics Theory Study Tapes
- Novice Study Tapes--1 tape
- General Study tape~--2 tapes
- Advanced Study Tapes--2 tapes
- Extra Study Tapes--1 tape
- ARRL Question and Answer Book for:
- Running Your Own Ham Station--2 tapes.
- Varifilter Instruction Tape--1 tape.
- Volunteers Services for the Blind, 919 Walnut St., Philadelphia, PA 19107, has in braille: " Blind Data Processor"--6 issues for $39.00. They also have a selection of IBM manuals in thermaform .
- American Printing House, 1839 Frankfort, Louisville, KY 40206, has available: "Transistor Electronics," Gerrish, H., Goodhart, Wilcox, 1969. T-2533.