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Making and using a leaklight

In my article on Testing For Leaky Pads, I covered the technical details of how and why leaks occur, along with their effects and a practical means of detecting them. In this article we're going to look at leaks in a little more detail, and learn how to use (and build) a leaklight - and so as not to cover old ground I'm going to assume that you've had a peek at the other article and you're all boned up regarding the theory.

Using a leaklightThere are four sections to this article, but if you're champing at the bit to find out how to make a leaklight, please feel free to skip ahead to the relevant section.

A leaklight does exactly what it sounds like it does - it lights up leaks. It sounds ideal - and yes, when used properly it's a valuable diagnostic tool. It's efficient, it's fast and it's simple - but there are a few caveats you should be aware of.
There are two requirements for a well-set pad - one is that the pad seats all the way around the tonehole, and the other is that it does so evenly. A leaklight is good at showing whether the former is true, but not so good at showing the latter.
You could argue that one a pad is seated, and a leaklight shows no visible gaps, then the job's a good 'un - and there's no need to worry. And this is true, up to a point - and the point is that you want to know that the seat is going to hold over a wide range of operating conditions, and that it is going to last for at least as long as the pad is in good condition.

The operating conditions are the varying pressures used to close the keys (you might press harder or more softly depending on how fast you're playing), the stability of the keywork (it may flex in use, or there may some free play in the action) and the degree to which the pads swell or contract as they go through the wetting/drying cycle. So it's clear if the pad is going to be able to cope with all of this, it's going to stand a much better chance of doing so if the seat is even all round.
This is why I always defer to the feeler test (as detailed in the earlier article), and use it in conjunction with the leaklight. I call it the 'show and tell' method; the leaklight shows you whether a pad is sealing or not, the feeler tells you how well or not it's seating.

But surely a chink of light shining through a tiny gap is going to be far more accurate than (in relative terms) a dirty great lump of paper or cellophane?
To understand why this isn't always so it helps to think in terms of a leaklight as being 'digital' and a feeler as being 'analogue'.
Something that's digital has but two states - 1 and 0 - or on and off. There's no inbetween, no half or quarter measures. As long a the pad seats well enough to block out the light, you'll see no light.
Something that's analogue has a wide range between two points.
Pad seat pressureThis diagram shows a pad seat that's being tested with a feeler - a previous test with a leaklight having only shown a leak at the 9 o'clock position on the pad.
The feeler is inserted between the tonehole and pad, the key is brought down with a gentle pressure and the feeler is withdrawn. The numbers represent the force required to withdraw the feeler (and thus the downward force of the pad against the tonehole rim).
As you can see, the numbers aren't equal all the way round. Some areas are clearly 'biting down' harder than others. You'll note that it's mostly a gradual progression - and a sudden drop in the numbers most likely indicates a leak. The light showed a leak where the feeler gauge registers a 2 on our 'grip scale' but showed nothing where the grip dropped from 5 to 4.
This slight drop might indicate a number of potential problems; perhaps there's a slight warp in the tonehole, or maybe the key cup is distorted. It could also mean that the pad isn't as flat as it ought to be, or that it might have shrunk a little. It may well still be sealing - but the feeler shows that it's a weak spot that's likely to degrade into a full-blown leak in the not-too-distant future. As long as you're aware of this limitation when using a leaklight, you won't go far wrong.
I should say that it's possible to use a leaklight in a more 'analogue' fashion, but it requires a very good light, a familiarity with the type of pads being used and a fair degree of skill and patience. And even then I personally wouldn't completely trust the results.

Leaklight in a fluteAnother caveat is that leaklights don't work so well when the pads are translucent - such as with skin (or 'bladder') pads, commonly used on flutes and clarinets etc. It's not that they can't be used, it's just that it takes a very practised eye to distinguish between the light that shines through the skin of the pad, and that which shines through a leak. And the smaller the leak, the harder it is to spot it among the ambient light. As with any tool, the outcome of the job it's being used for depends on understanding the requirements of the job (as just discussed) and the strengths and weaknesses of the tool itself - and to fully understand the capabilities of a leaklight we need to indulge in a little light theory (just couldn't resist a pun).
Light travels in a straight line - from its source to the target. It doesn't usually bend...unless you happen to live next door to a black hole. It can, however, bounce or reflect off objects in its path - losing more or less of its energy each time it does so depending on the nature of the surface it hits.

Understanding this property is key to using a leaklight; if you simply stuffed one down the bore of a saxophone you might well spot a few leaks, but there's a very good chance that you'd miss just as many.
This diagram shows a point of light shining in the bore of an instrument.
The spread of light will depend on the type of bulb being used. Something like a neon tube light will throw light in all directions; a single bulb might be more directional.
On the face of it, it looks like all you need to do is light up the bore of the instrument and all will be revealed - but it's a little more involved than that. Consider the following scenario. You're practising in a room - and being late night you have the light on. You can clearly see the contents of the room. While changing a reed you manage to drop one of the ligature screws on the floor, whereafter it promptly rolls away out of sight under the sofa. So you bend down to have a look - but it's dark under the sofa...even though the room is lit.
Clearly you're going to need more light - which would mean bringing the room light down to the level of the floor. This isn't usually possible - so you reach for a torch. This allows you to shine light directly under the sofa, at which point you are able to see and retrieve the ligature screw.
You could always increase the overall level of light in the room - if you got it bright enough even the most unreflective of surfaces would reflect sufficient light to allow you to see under the sofa...but again, this isn't always possible. So you can think of the bore of the instrument as being 'the room' - and the point at which the pad meets the tonehole rim as being 'under the sofa'.

Here's an extreme close-up of the pad seat which should throw more light on the subject (yep, another pun...just can't help myself).
Although the repairer's mantra is 'a flat pad in flat cup against a flat tone hole', in practice there has so be some allowance for the 'organic' nature of the pad. A pad seat is, effectively, a crease in the surface of the pad - and thus in the underlying felt core. This can lead to slight bulges either Close-up of pad seatside of the impression, which you can see (exaggerated) in this diagram.
This, combined with other factors such as the condition and cleanliness of the pad, the profile of the tonehole rim and the state of wear in the action can lead to 'false positives' when checking the pad seat with a leaklight.

Note the arrows depicting beams of light. The ones on the left would show a false positive. Although they illuminate the bore of the instrument and the surface of the pad, they're not at quite the right angle to shine through the gap between the pad and the tonehole. Strictly speaking they should never do so anyway...what you should see is the reflection of light hitting the pad. And this is a crucial point.
Pad leather isn't very reflective at all, so in order to see a leak in the diagram above, you'll really need to light up that section of the pad where it meets the inner surface of the tonehole wall - as denoted by the beam on the right. And just as with the room analogy, so it is with the leaklight - you either need to move the light to get the best angle on the seat...or you need to make the light a good deal brighter.

Making the light brighter carries a few problems with it, because it really has to be very bright. That means more power, and that usually means more expense. It might also mean that more care is required when handling the equipment, particularly if the leaklight is mains powered. That places such devices beyond the remit of this article - given that it's more for home tweakers rather than pro repairers - and let's be honest, few of you are going to want to shell out in excess of a hundred quid just so you can spot the odd leak from time to time.

So, we need a budget solution.
In years gone by this would have involved all sorts of lash-ups; with torch/flashlight or car headlamp bulbs, or short fluorescent tubes. None of these solutions were particularly effective or safe - but lighting technology has moved on a lot in recent years, and there are now some credible options in the form of LEDs.
Because you're reading this article it's quite likely that you've already looked around to see what's available on the cheap - and I'm willing to bet that all you found were flexible (or rope) lights. In theory these sound great, but in use they often have a number of drawbacks - chief of which is that they simply don't last that long. While it's undeniably convenient to have a leaklight that can be bent around corners, it means that the conductor that supplies power to the light must also bend...and because these things are built to a price it means that the conductor isn't really beefy enough to last for any real length of time. It's also often the case that these lights have a comparatively low output - so even if they do work, they don't work very well.

What's needed is something that's sturdy, yet small enough to fit within the bore of most instruments, that's safe to use and that chucks out enough light to make it useful. And you'll be delighted to hear there are a couple of options...though at this stage I'm duty bound to point out that you undertake any of the following at your own risk.
Which one to build will depend on your needs and preferences. The first is what's known as a 'single-point light source' - essentially a single bulb - and the second is a 'multi-point light source'...AKA a striplight.
The advantage of a single bulb is that it can be positioned to light up just a single pad (more or less) without spilling too much light onto adjacent pads, and you're more likely to be able to get it around corners. The striplight's main advantage is that it will light up several pads at once, which makes it more useful for quick diagnosis and for assistance when regulating key groups. It's much better to have a whole stack lit up than have to move a single light back and forth with every adjustment. Its big disadvantage is that it's not so good at going round corners, and the light from adjacent toneholes can mask very small (pinprick) leaks from the pad under scrutiny.
Both lights have their uses, but if you were going to choose to make just one then I'd recommend the single-point light.

First up though, some important technical stuff...
These lights are low-voltage solutions (12 volts DC) - you don't need any more power than that these days, and even I'd think twice before using a mains powered light down the bore of a metal tube - and the first thing you'll need to source is a suitable power supply.
AC/DC power supplyThis shouldn't be too hard - I'm willing to bet that most of you have a spare 12 volt power supply kicking around the house somewhere, but if not you'll have to buy one. For safety's sake it's better to pay a bit more and get a branded power supply rather than a cheapo ebay special, because some of them are particularly nasty. A lot of internet routers use a 12 volt supply, and as we all seem to have a cupboard full of knackered old routers, it's a good place to look for a decent PSU (power supply unit - also sometimes known as a 'wall-wart').
It doesn't have to be a very powerful one - these lights only draw around 1.6 watts of power, and if we do the sums (Amps = Watts/Volts) we end up with 1.6 watts divided by 12V = 0.133 amps (or 133 milliamps...also written as 133mA). This is quite a low power requirement; you'll probably find that most 12 volt power supplies are 'rated' at 300mA or above...and often at 1 or more amps. Anything that's rated at 200mA or above will be fine.

Here's one that's ideal for the job, it's off an old NiCad battery charger.
As you can see, it's an AC (mains) to DC adapter. Beware of AC/AC adapters - if in doubt, check the output specs. It should say what the type of output is, either DC or AC, but you might also see a little symbol. On this power supply you can see that just after the 'Output : DC12V' there's a pair of lines - the upper solid, the lower broken. This is the DC symbol. You can see the AC symbol in the line above...it's a single wavy line. You can also see that it's rated at 700mA, which is plenty more than is needed. Note too the diagram for the polarity of the output plug.

Power supply plug polarityMost power supplies are fitted with an adapter plug (the output plug) which fits into the device they're intended to power. If you look on the supply casing it usually has a little diagram which tells you the polarity of the plug. This will be in the form of something like a capital C with a little dot in the centre - each with a line attached to it that terminates in either a + or - symbol. In most cases the C is negative and the dot is positive...and on the output plug itself this translates into the outer tube being negative and the inner positive.
You may need to cut this plug off, depending on which build option you go for, which might leave you wondering which wire is the positive and which is the negative. As a very general rule of thumb the PSU cable will either be a 'flat twin' (as shown in the plug shot above) or a single shielded cable with a woven 'shield' around a central core. Flat twin cables often have markings on one of the pair, such as a white or coloured stripe - and this usually indicates the positive cable. For shielded cables it's nearly always the central core that's positive. There's no need to worry too much about this for the following projects.

Failing all that you can opt for a 12 volt battery as your power source. I wouldn't recommend using a car battery due to the sheer weight of the things and the risk from acid spills and explosive gases - and would instead suggest a Sealed Lead Acid (SLA) battery. These things are used in burglar alarms, model cars etc. and are readily available and reasonably cheap (just Google '12V 1.2AH SLA battery')...though you'd need to invest in a suitable charger...and if you buy a charger you might as well use it to power your leaklight. On a note of safety, you can't use a car battery charger on an SLA battery...though you can use it to power the leaklight...

You can also use a 9 volt battery. The light will be rather dimmer, but it will still be bright enough to be usable. The obvious choice is the standard PP3 9v battery - which is typically used to power all sorts of small gadgets such as clocks and radios etc. - but there's also the rather less common PP9, which is rather larger. In both cases you'll need to buy a 'battery snap' connector to enable you to connect the leaklight up to the battery. It might be worth checking out the battery compartment on any old toys and gadgets for salvageable connectors - otherwise they're cheap enough to buy on ebay.

You're also going to need a few tools and supplies. The absolute minimum is some insulating tape (sellotape will just about do) and something that will cut small wires. Thereafter some heatshrink tubing would be handy - and for a really reliable job, a soldering iron and some solder. Some epoxy glue will be handy, but for an easier job you might want to look out for some epoxy putty. Don't get any of the metallic types though as these may be electrically conductive, which may lead to short circuits...which may lead to a small domestic fire, some frosty looks from your parents/partner, a lot of swearing and shouting and an unusual insurance claim. You might also need some wire, the choice of which will become clear as we go along.

Let's start with the single bulb build, as it's the simplest.
G4 LED bulbsIt uses this wee beastie...a G4 LED bulb.
These little gadgets are a boon. They're dead cheap, reasonably tough, come in a variety of sizes and put out an enormous amount of light for their size. Better still, making a leaklight with a G4 bulb is a cinch - and it can be as easy or as complicated as you like, depending on how handy you are with a soldering iron and a tube of epoxy resin glue.
First up, though, you need to get the right bulb.

The G4 series of bulbs is, essentially, a couple of circuit boards with varying numbers of LEDs fitted to them (known as SMD construction)...the whole of which is encased in a clear silicon gel 'capsule'.
Some are designed to be powered by mains voltage, others will handle either AC or DC volts - but the ones we want should be listed as requiring 12 volt DC.
Various sizes are available, but I doubt you'll ever need anything much brighter than a 24 LED bulb (on the left of the pair of bulbs), which is generally rated at around one and a half to two watts output and has a diameter of just under 10mm. This is small enough to fit down most instruments, and will even go all the way up to the upper octave pip on a sopranino sax. You can get bulbs with more LEDs, and these will be brighter (typically 2-3 watts with 48 LEDs, shown on the right of the pair of bulbs, and 3-4 watts with 64 LEDs) but will also be larger. These larger bulbs are seriously bright, to the point where looking at them will hurt your eyes - and you simply don't need that much light for the job.
LED lights often have a 'polarity', which is to say that the positive from your power source must go to the correct connector on the light and the negative likewise, otherwise the light won't work...or you might even ruin it. Fortunately this fussy business is all handled by the circuitry inside the G4 bulb, so you can connect it any way you like with no problems at all.

You have a number of options when it comes to connecting the bulb up to a power supply, and at the very simplest you could just attach the supply wires to the prongs on the bulb, connect up or switch on the power supply and Bob's your uncle...let there be light. It works, but it's not very practical - though that's easily remedied by simply taping a stick to the PSU leads, so that you end up with something that looks a bit like a novelty magic wand. If you leave the last couple of inches of cable free it'll even go around a corner...though I dare say the wires will break sooner or later.
However, if you want to improve the functionality of your leaklight with hardly any extra effort (and expense) you're going to love this next little handy hint.

Cutting the cableGet yourself a length of 2.5mm flat twin and earth cable. This is the stuff that's used for wiring up house sockets and the like, and there's a good chance you've got some knocking around in your shed. If not you can buy short lengths of it very cheaply - just type "2.5 twin and earth cable" into an ebay search and check the listings until you find someone who sells short lengths. I found someone selling a metre of it for a couple of quid.
Having got your cable you need to strip the outer insulation back on one end by about an inch or so, revealing the three cores (red, black and the uninsulated earth wire). Cut the earth wire off - you won't need this.
Now strip away a section of insulation on the red and black wires - you'll connect your power supply to these. You can either solder the wires on or wrap them around each other and secure them with tape - or use a cable connector block.
Using a cable connector blockNow you need to cut the cable to length. What length is best depends on what horn you have; ideally you'll want the cable to run the length of the body...from the top of the crook socket to the centre of the low Eb pad. You might also need to take into account the size of any connectors, which might not fit through the crook receiver socket.
If you've opted for soldering or wrapping the wires, or are using some form of plug and socket that will fit through the crook receiver, you can cut the cable shorter. I'd say a foot is about the shortest length that's useful.

This is the really cool bit. If you look at the end of the cable you'll see that you've got the red wire, the central earth wire and the black wire...and if you place the prongs of the G4 bulb up against the cable you'll see that they match the centres of the red and black wires perfectly. If they don't you've either got the wrong bulb or the wrong cable.
Starting with the red cable, carefully ease one of the G4's pins between the core of the wire and its insulation at either the top or the bottom of the wire. Go gently, you don't want to bend the pin - all you're trying to do is just make a neat entry hole. You might find it helps to use a needle to make an initial entry point between the insulation and the wire - and if you find that the way the wire has been cut makes it difficult, cut a little off the end of the cable and have another go.
Fitting the bulbNow do the same with the black wire, in the same position you poked the hole on the red wire. Now poke both prongs of the bulb into the holes at the same time...and carefully push and wiggle the bulb all the way in. The bulb is semi-soft, so it won't shatter and cut your fingers.
It might help to connect the power up while you do this, just so you can check the prongs are making good contact with the wires.
And that's essentially it! The prongs on the bulb are long enough to hold it secure, the insulation on the wires is tough enough to act like a sort of socket - and best of all, the cable itself is stiff enough to stay straight in use, but can also be bent when you need to get the bulb around a tight corner. If and when the bulb connection gets a bit iffy, cut a centimetre off the bottom of the cable and make a pair of new holes.
The very best part about this light is that it can be as powerful as you'll ever need depending on what bulb you use, and it's fantastically cheap. Excluding the power supply you can knock this nifty gadget up for as little as two quid. Now that's what I call a proper bargain.

PP3 powered leaklightOn the right is my PP3 leaklight. This is pretty much as basic as it gets - it's a 24 LED G4 bulb pushed into some twin and earth with a 9 volt PP3 battery powering it. I've spruced it up a bit by using some heatshrink to insulate and secure the connection between the battery snap and the twin and earth cable. Given that the cable and battery snap were salvage parts, the only expense here was the bulb, the battery and the heatshrink. It's a poundshop battery (two for a quid) - so that's 50p for the battery, 64p for the bulb and let's say 10p for the heatshrink. That comes to £1.24.
As you can see, it's pretty bright even in only a moderately dark room (daytime, with the lights out and the curtains drawn).
You might be wondering how long the battery will last. A fresh battery measured 10.2V, and after an hour and a half of continuous use it measured 8.8v - by which time the light was noticeably dimmer (though still usable). I dare say you'll get more out of decent alkaline battery rather than this poundshop cheapy, but bear in mind that you won't be using the light constantly for an hour and a half.

G4 bulb socketsThe next step up is to buy a G4 socket for the bulb. These are readily available, and dirt cheap. There appear to be two types; plastic and ceramic - and I'd probably go with the ceramic ones.
These come pre-wired - so if you don't have access to a soldering iron you can just strip away the insulation on the end of the PSU cable, wrap the wires around the 'tails' on the socket, and insulate them with a bit of sellotape (hint: make the wires uneven lengths to reduce the risk of a short circuit). In the event of the bulb failing it's just a matter of pulling the old one out of the socket and plugging a new one in. You can also upgrade to a brighter bulb should you ever feel the need to do so...or even go for one of the smaller ones.
I've attached a socket to my 'two quid leaklight' by simply exposing half an inch of wire, removing most of the insulation and poking the wires straight into the base of the socket (they're almost a perfect fit). I had hoped that they'd be the right size to squash up against the connectors inside the socket - but no, not quite, so for an effective electrical connection you'll need to attach the tails to the wire. I've done this by soldering them in place...but you could just as easily wrap the (stripped) tails around the wire and slap a load of epoxy glue on to keep them in place. If you really wanted to go the whole hog you could extract the sleeves from the socket and solder the power leads directly to them. Removal of the sleeves is done by pushing down a small locking tab (visible though the little slots just below the head of the socket) while pulling gently on the cable. When refitting the sleeves, don't forget to raise the locking tab otherwise they'll just pull straight out again.
Some heatshrink over the connection and the base of the socket would really tidy things up a treat. At the very least I'd wrap some tape around where the wires are joined, just to prevent a short if the wires get kinked. If there's a drawback it's that the socket extends the non-flexible portion of the light - though not by much.

G4 LED leaklightsAfter that you're into serious geek territory, and with a few tools and a handful of (cheap) supplies, you can make quite a respectable leaklight.
The largest of the lights shown here uses the flexible metal tube (known as a gooseneck or a Stay-Put tube) salvaged from a broken USB webcam. It's actually quite hard to buy this flexible tube on its own, so you'll have to look around for cheap gadgets that use it and break them down. Desk lamps are a good source. This tube measures 6mm diameter, and the bore is large enough to fit a pair of 24 AWG silicon wires through it. I chose this type of wire because it's very flexible and is less likely to break due to constant movement.
A couple of things are worth bearing in mind; you don't want too thick a tube (which tends to rule out microphone goosenecks, which have a diameter upwards of 10mm) and too thin a tube (5mm and smaller - as used for the light in the middle) may present some problems when it comes to finding suitable wire that will fit down the tube...though such tubing will make it easier to get the light into tight spaces, such as into the bore on a baritone sax via the low D or C tone holes. I've fitted heatshrink over the tubing to prevent it scratching lacquered finishes. It works very well, though it slightly reduces the flexibility of the gooseneck.

Threading the cable through the gooseneck is a bit of an adventure. If the cable's stiff enough you might be able to thread a pair through with no problems, or you might find a spot of lubricant helps things along. A silicone-based lube is ideal, but you could also use a little washing up liquid.
If your cable is very flexible (like the silicone wire I used), you'll probably be out of luck and will need to be a little more Threading the cablecanny. What I did was to push a single wire through the gooseneck and then superglue it to the pair of cables. You'll need to lay the pair of cables side-by-side, then lay the single cable in the 'groove' between the pair...thus making a sort of pyramid (if you lay the cables out three-abreast it's unlikely they'll go through). Pop a spot of glue on, let it set, then pull the single cable through and it'll drag the pair through with it. If this fails to work you might have to strip the insulation back at the ends of the cable and twist them around each other...or you could just solder them together.

I've also gone for a 'modular' approach to the power supply connection. By fitting a socket to the end of the leaklight (with a corresponding plug on the PSU lead) I'm able to use a number of lights with the same PSU. I've also used locking plugs. These aren't necessary - but if you're using the lights on a daily basis you don't really want to have to muck about with plugs coming adrift when you're checking for leaks. If you'd like to use these you'll find them on ebay listed as a 'screw locking DC plug' - and you'd be well advised to source the socket from the same supplier (so that they match). The dimensions are 2.5mm diameter for the central pin and 5.5mm for the plug's outer connector.
Having access to a lathe I've also knocked up some custom 'end pieces' in which the light and power sockets are glued. Again, not really necessary but a useful addition if you're using the lights regularly. No lathe? No big deal - you can glue the sockets in place with a non-metallic epoxy putty. In some cases you might even be able to use the fittings already attached to the tube if you're salvaging it from, say, a flexible desk lamp or a webcam. You can also make custom 'cones' from heatshrink tubing - all you need to do is find something suitably tapered to use as a mandrel (paint brush handles, cutlery etc. - or you could always whittle a stick down). Pop the heatshrink over it, give a bit of heat (just-boiled water works) and the tube will shrink down onto the mandrel. This will leave you with a cone, which can be fitted over the cable and act as a housing for a socket. Once you've wired it up, simply fill the cone with epoxy adhesive and allow it to set. 10mm heatshrink should be fine for this purpose.

For the twin and earth '£2 leaklight' I've kept the build quite simple. I've soldered the lamp socket in place and on the other end I've soldered a 2.5mm headphone jack socket. I've wrapped tape around any exposed wires and then popped a length of 10mm heatshrink over the connections and shrunk it down with a lighter. Technically speaking, the two sockets and the heatshrink have blown the budget, so I suppose I'll have to call this the £3 leaklight. But you can see that you can make a very decent leaklight for just a couple of quid - and with a little extra effort (and a handy box of assorted bits and bobs) it's pretty easy to customise the light according to your DIY skills and your budget.
And how long will the light last? The gooseneck solutions should stand a great deal of use, though much depends on the quality of the gooseneck and the type of cable inside it. As for the twin and earth light - well, in the interests of science (but mainly to put the mockers on whingers claiming the cable will break after a week) I connected a 2 foot cable up to a power supply, fitted a 2 watt bulb and sat here bending the cable (from a horizontal position) straight up to the ceiling and then straight down to the floor. That's 180 degrees, in the same place every time. I got up to 500 bends before I gave up out of sheer boredom - and the light was still shining. You're not likely to ever need to bend the cable 180 degrees - but assuming you did, and assuming you checked your horn for leaks every week, you'd get at least ten years out of the light before the cable broke.

Biard LED lightThe next build project is potentially rather more complicated, and a little more expensive. It's a multi-point light source based around - believe it or not - a caravan light.

It's just an aluminium tube with 20 LEDs fitted to a strip in a cutaway, and it's powered by a 12 volt power source. They're widely available from places like ebay from around £10. There are a few variants of the same light - some are longer, and some come with a switch attached to the bottom. I doubt you'll need a light that's much longer than this one (35cm), but if you feel you do it's worth bearing in mind that the unswitched ones are modular - which means you can connect two lights together. I would say that the switch isn't necessary if you're only going to be using the light occasionally. LEDs have a very long service life, typically tens of thousand of hours, so leaving the light on isn't going to damage it...and I've found that the switch, which is fitted to the bottom of the light, sometimes catches on obstructions in the bore and switches the light off. No big deal, but it gets annoying quite quickly. The end where the leads are fitted is a removable plug and on the other there's a removable endcap.
If you want to search for one of these lights, it's made by Biard and the model number is LEDTSMD20DC - or you can just do a search for a 12V LED caravan light.
This light has a number of things going for it; the casing is tough...so it'll stand a drop, or even being trod on; it's stiff...so there's no risk of it bending and breaking the internal conductors; it's bright and because it can be powered by either a 12 volt battery or a 'wall wart' power supply, it's safe.
It has some drawbacks though - the lack of flexibility means it won't go around corners and it doesn't come 'ready to go' out of the box...which means you're going to have to do a spot of (simple) wiring. And, as before, you're also going to need to source a power supply.
Like the G4 bulbs it'll work with a 9 volt battery, though it won't be as bright as it would be with a 12 volt supply - and because the LEDs are more spaced out, the light is less concentrated. It's still usable though, and the runtime should be much the same.

Unlike the G4 LED bulbs, you're going to have to take the polarity into account when wiring up this light. This means that the positive lead or terminal on your power supply/battery must connect to the positive lead on the light - and the negative to (you guessed it) the negative. If you're lucky you'll see a couple of symbols denoting which lead/terminal is which - a '+' for the positive and a '-' for the negative.
This is because LEDs typically have a 'driver' circuit, and like most circuits it won't work if you mix up your positive and negative. There's also a chance that you might damage the circuitry if you 'reverse the polarity' (something that often works in Sci-fi, but seldom in real life). But how to tell which wire goes where?
Fortunately the Biard LED light has a little sticker attached to one of the leads with the + symbol on it. To make it even easier, the lead has a red stripe along it - so that's one uncertainty taken care of.
If you're going to use a battery you'll find that the terminals should be marked in a similar fashion - just connect the + lead to the + terminal and the other lead the negative and all will be well.

If you're still uncertain there's one sure-fire way of determining which wire is which (assuming you haven't got a multimeter handy) and that's to connect the light up and see what happens.
Now I know this sounds bad, but I've tried it and it's fine. Nothing goes bang or catches alight. However, there's still a risk that you might damage the circuitry, so it will pay to be quick when it comes to carrying the test out.
If you have a power supply with a hollow, round output plug on it, push one of the wires down the central tube (try the positive first) and then briefly touch the other on the outer tube. If the light comes on you've got the wires the right way round...if nothing happens, swap them about and test again - and make sure the wire inside the central tube is making good contact.

If your power supply doesn't have a plug (or has a different kind of plug), the same rules apply...hold one of the light's wires against one of the plug's terminals or the bare wire, and briefly touch the other light wire against the other terminal/wire.

Bare leadsHaving decided on a power supply and sorted out which wires go where, it's time to wire things up.
How permanently you do this depends on whether you want to use the power supply for anything else - in which case it'll boil down to wrapping bits of wire together and holding them in place with sticky tape. A better bet would be to source a power supply socket and wire that to the light, though I'd recommend extending the lead out of the light first so as to avoid the power supply socket going down the bore of your instrument.
Socket to screw terminal blockOne very useful gadget - pointed out to me by Steve Marshall, a fellow woodwind repairer - is a Socket to Screw Terminal Block. This allows you to plug a power supply directly into the block, and then connect the leads of the light to it...so there's no need to cut any wires from the power supply. You could simply connect the light to the block (maybe wrap a bit of tape around it, to stop the PSU plug being pulled out) and away you go.
Bear in mind, though, that the connector block might not go down the bore of some instruments (you should be OK with saxes). The connector blocks are widely available online for just a few quid - but you will need to match it to the size of the PSU plug.
Because I sometimes work away from the workshop I need a portable setup, and this is based around a small 12 volt lead acid battery which is housed in a case with a 1/4" jack socket output...so I'm using an old guitar lead*. The principle is the same though, there are two wires - one positive and one negative - that have to be connected to the light's lead. This would be much the same as you'd see if you cut the output plug off the power supply lead and stripped the insulation back to expose the wires.

* I found the guitar lead wasn't so great in practice because the inner wire tended to break. I replaced it with 1.5mm transparent speaker wire (total cable width approx 6mm). This cable is more flexible than standard twin core, and a couple of metres is only about a fiver.

HeatshrinkI want to make a neat job of it, so I'm going to solder the wires together and insulate the joints with heatshrink.
I've shortened the light's lead so that the cable joint is nearer to the end of the light - and I'll incorporate the joint in the strain relief. If you're only going to be using the light occasionally you probably won't need to do this...but it makes for a nice, long-lasting job.
I've got some heatshrink on the leads coming out of the light, and I've made a 'cone' out of heatshrink to cover the connection which I'm going to fill with Sugru later. Note the additional piece of black heatshrink on the end...this is because the red heatshrink doesn't go down small enough to grip the cable.
If using heatshrink, remember to put it over the cable before you connect the wires up...or you'll have to undo them to get the stuff on. Yep, I did that.

Filling the cone with SugruI've soldered the leads together (and tested the light) and now I'm filling up the heatshrink cone with Sugru.
Once it's set it'll provide a solid but flexible support for the cable, which should help prevent the wires from breaking.
As you can see, it's nothing particularly technical - I'm just squishing the Sugru in with a stick.
Pack it in firmly so that when you squeeze the cone gently you can't feel any obvious air pockets.

If you didn't much fancy faffing around with the heatshrink you could simply mould the Sugru around the cable. This would be just as effective, though it would take some time to cure...and you'd need to wrap some tape around the joint between the Sugru and the top of the light.
As for how much Sugru you'll need - I stuffed a whole sachet into my cone.

Strain reliefOnce filled, I've pushed the cone over the end of the light - it should go on about a centimetre or so.
There's a good chance that it will now slowly slide back off...in which case you'll have to dig out some of the Sugru and try again. This is a bit fiddly, but given that it takes a day or so for the Sugru to set, you've got plenty of time. I got a bit impatient and cleaned the end of the light up with cigarette lighter fluid, ran some superglue around the tip and shoved the heatshrink back on. That did the trick.

Taped strain reliefTo finish up I've wrapped a piece of insulating tape around the end of the light.
I've found this is necessary otherwise the end (which is a plug) will eventually drop off in use, which is a nuisance. You could always glue the plug in place, but taping it on will allow you to remove the plug at a later date should you ever need to change the light itself. Having spent so much time knocking up a nice lead, it seems silly to throw it away if ever you needed to replace just the light fitting itself.

Sawn off tipAnd that's about it.
One last 'mod' I did was to saw off the plug socket at the other end of the light. This is just a plastic affair with a couple of pins running through it - and using a junior hacksaw I sliced through the plug about a millimetre from the end of the light tube (the plug itself doesn't appear to be removable). The reason for doing this is to shorten the distance between the end of the tube and the LED on the very bottom, which will help when it's being used down at the bottom bow on a sax.
It's not a good idea to leave the pins exposed, so you can either stick a bit of tape over them, dot a drop of paint or nail varnish on them...or simply cover the end with any leftover Sugru.
If you're at all worried about the end of the tube scratching the bore of the instrument you could always wrap some insulating tape around it or seal it up with some heatshrink, and if you've left the original endcap on it's probably worth glueing or taping it on anyway.

Cork stopperWhat you need to do now is nip out and buy yourself a bottle of Champagne. You've earned it, after all, and better still you have a bona fide excuse to do so.
As good and as bright as this light is, it suffers from being rather directional. Obviously you're not going to get any light coming out of the back of the tube - and what light comes out of the front is shielded by the walls of the cutaway in which the LEDs sit.
This means you have to rotate the light in order to get the best angle on the pads, and rather than having to hold the light in place while you check for leaks it would be better to have some means of securing it. Hence the bottle of Champagne.
As you can see I've removed the cork from the bottle and, some time later, drilled a hole though the middle of it and then cut a slot down the length with a saw. Some trial and error is involved, depending on the thickness of the cable and how much of the Champagne you drank - so it's best to start with a small drill/slot and increase as necessary.
If you get it right the cork should be a snug fit on the cable but should still be able to slide up and down...and when placed in the crook receiver it will lock the light in place. You may need to cut and sand the diameter of the cork to fit. You might well find that the directional nature of the light can be an advantage sometimes as it allows you to regulate just how much light shines onto the pads. In some cases this can give you a better idea of how big or small a leak is.

You may need a number of such corks in various sizes for various instruments (flutes, clarinets etc.) but in practice I find that I only need the locking feature for saxes. You might also need a similar system for the G4 lights - not so much to control the direction of the light but merely to keep it aligned with a particular pad. If you're using a gooseneck or the twin and earth cable, you can just bend the shaft/cable where it exits the crook receiver.
Now I know I said Champagne, but you might have to go through a number of bottles of various 'sparkling wines' to find a cork that's large enough for the job. I know I did, which is why I can't now remember where this particular cork came from. It might have been from a bottle of Cava...or even some of that supermarket 'Bucks Fizz'. Whatever it was I probably enjoyed it...

If all this seems like a lot of hassle then it's worth considering some of the alternatives.
As I said earlier, I don't much rate those flexible lights though it's clear they'll be better than nothing - and you might be better off looking for something else, such as these items shown on the right.

Number 1 is a flexible inspection lamp (I think I got it from a diving equipment website). It takes two AA batteries and has a reasonably bright LED on the end of a flexible shaft. It's not as useful as the custom leaklights, but it really comes to the fore when you have to examine the top bow pads on a baritone. Costs about £20 though, so it's not exactly cheap.

Number 2 is a USB LED desk lamp, purchased from a Pound Store for, well, a pound. It's cheap and it's crappy - but it works, and it works quite well. In order to make it usable you'll need a USB extension cable (cheap enough), and you'll probably want to pop a spot of glue or tape where the flexible shaft connects to the light as it's a bit weak there. Like the caravan light, it's directional, so you'll need to move it around to position it under the pads - and for smaller instruments you might find the USB plug won't go up the bore. But for a pound a pop you can't complain. It'll work off a computer USB port, or a suitable USB wall wart power supply.

Number 3 is a 'zoomie' torch (or flashlight). This is the ubiquitous Sipik SK68 - at least that's what it says on the side. In fact it's probably a clone or a copy - there are lots of them (often under the Ultrafire brand). The light runs off a single AA battery and has a very bright single LED in the head. Being a zoomie it means you can focus the beam, which makes it useful for shining down a bore. You won't be able to push the torch itself down the bore of an instrument, but you can often shine the light in through an opposing tone hole...or shine it onto the exterior of the pad and see if you can spot any light leaking into the bore. They're widely available on ebay (search for 'Q5 zoom torch') for about a fiver. I've got about half a dozen - they're ideal for general household/car use.

Number 4 is small but very powerful (72 lumens) LED torch that uses a single AAA battery. It's small enough to go down a bore, and while the beam won't shine directly onto a pad it's still wide enough to make it usable. It's small enough to be able to be pushed into a length of garden hose pipe or taped to the end of a stick. A neat trick is to stick some silver foil to a small piece of card (2cm x 3cm) and then tape it on to the side of the head of the light (foil inwards) so that it acts like a mirror and reflects some of the beam at 90 degrees to the head. This particular light is a Fenix LD01, so it's bit pricey, but cheaper lights of a similar style can be found - and anything that's around the same size that puts out more than 50 lumens will do.

Otherwise, just keep your eyes open whenever you find yourself in the sort of shop that sells gadgets. For example, I was shopping for some bits and bobs in the local hardware store recently and I spotted a handy-looking LED strip light. It's the Osram LEDStixx. It's powered by 3 AAA batteries and has 4 LEDs set into a short, narrow tube that will easily fit up a the bore of a flute (and perhaps even a clarinet). It was on sale for a tenner...and with a short length of garden hose (to push the light into as a holder) you'd have a basic but usable leaklight for the price of few beers. I would have bought one to test as part of this article...but I bought a few beers instead.

There are a couple of accessories that will help to increase the effectiveness of your leaklight, the first of which is simply a shaving mirror. Positioned appropriately it'll allow you to see the front and the back of the pad you're working on without having to heft the instrument around. Another useful accessory is a foot-operated desk lamp. A leaklight works best in a darkened room, and while it throws out enough light to be able to see what's going on, it's seldom bright enough to see by if you have to make any adjustments. It's a pain to have to keep getting up to switch the room light on and off, so some sort of desk lamp is a good idea - and if you can find one with a foot switch, so much the better.

Copyright © Stephen Howard Woodwind 2015