There are significant dangers in this field so.... please read this warning and play safe!

No Apologies!

You may be a professional, experienced engineer or simply seeking to gain satisfaction from a creative and enjoyable hobby.  We stress the dangers not to insult anyone’s intelligence but to ensure that you continue to enjoy your pastime  – in safety! [Special thanks to Malcolm Burrell for his help with this section.]

Mending old radios and TVs should be a pleasant pastime and relaxation, but don't relax too much. There is grief lurking inside every old set and whilst Gerry Wells at the Vintage Wireless Museum in London will cheerfully tell you of the first man to be electrocuted by a TV set, death is no laughing matter. So this section is intentionally laden with doom.

Many people who mistakenly feel that ‘old technology’ is somehow more user-friendly, in some strange way automatically good - merely because it is old.  Don’t be fooled! Approach old equipment with an open and alert mind and realise that a hot chassis, or a resistor line cord, or asbestos insulation, or selenium rectifiers require much more thought and consideration for safety. Remember, too, that the old-timers who talk so glibly about safety received an on-the-job training, having worked man and boy in the business. We enthusiasts are mainly part-timers or newcomers to the hobby and haven’t had the benefit of that training. And just because it’s a hobby, that doesn’t exempt us from safety drill. Live chassis are indiscriminate in whom they kill and even if you are a thoughtful, careful kind of person, that doesn’t mean the last person who handled the set was. Never drop your guard – you may know why wax was melted over grub-screws but another clown may not have done. He lost the proper grub-screws and used normal bolts… and the next person who grasped the on-off/volume knob of the radio wondered why it always gave a tingle! Does this sound tedious? It shouldn’t so, because safety is never boring.

SAFETY

Vintage radio and television receivers use 'live chassis' techniques, in which the chassis is connected directly to one side of the incoming mains supply. This means they can be lethal to carry out repair or servicing work on, unless the appropriate safety measures are in place.

These include feeding the supply to the set through a proper double-wound mains isolating transformer having an adequate insulationrating, thereby reducing the possibility of severe electric shock or death. A residual current device protector, on sale at all do-it-yourself shops, is a further precaution.

If you are not satisfied that you fully understand the risks involved in this sort of work, do not proceed any further. Instead seek advice and assistance from a competent technician or engineer.

Kitchen Chemistry

Hank Van Cleef has some strong words to say on what he calls "kitchen chemistry" and they deserve a wider audience. The kitchen makes a wonderful workshop for many of us. A kitchen is a place for food preparation, not chemistry experiments or industrial processes. Be very careful to keep solvents where they cannot contaminate foods or anything used for food preparation. Store chemicals separate from food items, and away from the inquiring hands of small children. Also keep in mind that many of the preparations sold in grocery stores for kitchen cleaning purposes are, in reality, very strong chemicals, and may have very little information on the chemical content or processes.

He continues that almost any solvent or process has safety considerations to consider... and almost any solvent or process will damage something in a device. You may want to use it over here on this metal part, but if you get it on that plastic part or electronic component, in may destroy it. Additionally, there are issues of fire hazards, fumes, violent reactions with other chemicals, and safe storage to consider. Some domestic oven cleaners are more violent than many an industrial cleaning processes, with labels giving a litany of safety precautions for their use.          

Hank concludes you should know your products and know your processes. Test powerful cleaning products first; many of the spray can cleansers that are so easy to use take off markings and finishes  along with the dirt. You have been warned!

Don't plug it in!

Whenever you acquire a new treasure there's always a terrific temptation to try it out. With mains-driven equipment that means plugging it in and seeing if it works. Well don't, not until you have made some quick checks. Is the mains cable (line cord) complete? It may have frayed or brittle insulation, allowing two wires to touch (or giving you a shock). An input filter capacitor (if fitted) may have broken down and could give a dead short. Electrolytic capacitors in the power supply may not be able to stand the surge of full voltage after many years of lying dormant. Plugging in elderly appliances without making first-line checks is asking for trouble!

Electricity Doesn't Warn You First

One side of the mains supply is 'live' with respect to earth whilst the 'neutral' side approximates to earth potential. A large number of radio and TV receivers were produced using the 'universal' or 'AC/DC' technique which permitted the omission of large, expensive mains transformers. When switched on these sets employed a chassis common to one side of the mains supply. Incorrect polarity of the mains input connection usually had little effect with AC mains operation but could result in the chassis being LIVE! Some more recent receivers have used a technique where the chassis is always at half the mains potential regardless of the polarity of the mains plug connection!

Another thing about live-chassis sets - live spindles. We’ve touched on this already but it’s worth making the point once more. The shafts of switches and potentiometers fixed to the chassis may well be at chassis potential and thus live. The bakelite or wood cabinet is insulated but these shafts are not, and if someone lost the proper grub screw and replaced a knob using a cheesehead screw, the next person to grip that knob may get a dose of 250 volts. Originally these grub screws were sealed and embedded in wax but you cannot rely on subsequent tinkerers having the same high standards.

Even in more orthodox apparatus standards of insulation were not always as high as they are now. Soldered connections to HT and mains wiring should always have rubber or plastic sleeving but in times gone by this was often omitted (or it may since have perished).  Beware too of kinked and frayed braiding on cloth-covered mains cords, particularly when the cord has a dropper conductor.

Isolate for safety

Anybody who employs staff to repair domestic electrical goods is obliged to provide isolating transformers for their use. They are not expensive, especially if you buy overstocks at swapmeets, and if they are good enough for employees, they must be equally good for equipping the home enthusiast's test bench. Only a fool would set a lower price upon life. 

Think: how often do you work on your own? If you had an accident and had to shout for help, would anyone hear you? If not, your personal safety must be worth the price of an isolating transformer. This is particularly vital with the adjustment and repair of TV receivers; these must be connected to the mains supply via an isolation transformer.  Note that a double-wound isolation transformer offers protection only when no more than one device is connected. If you connect two live-chassis items to an isolated supply and fail to observe 'polarity', you can end up with a false sense of security and 240V potential difference between the two items. In fact the wattage of isolating transformers is frequently restricted to minimise the risk of having two loads connected.

In field servicing this item is frequently considered inconvenient and engineers frequently service live equipment which is not isolated from the supply. The best advice is to keep one hand behind your back at all times you are working on powered equipment. If you need two hands, they say, you should find another way. It may be hard to comply but you should try. Also learn where the anode and screen pins are on the more common valve types (e.g.  pins 3 and 4 on many octals) and be careful around them. Keep your fingers off any terminal inside the equipment. Use good test leads and you won't ever need to touch anything inside (except possibly a control grid connection to see if it causes a hum – not the best technique but frequently used.)

Never assume anything!

So you've correctly connected the brown or red wire to the right-hand pin of your plug and the blue or black wire to the left-hand pin. So what? Did a D-I-Y enthusiast fit your mains supply socket correctly? Or has the connection of the mains cable to the TV been incorrectly wired at some distant point in time? Or perhaps the receiver mains switch is faulty or has had one pole bridged? Any of these items could result in a LIVE chassis!

Don't even rely on the judgement of others. I remember I was once preparing some flex using nature's own wire strippers (i.e. my teeth, not a clever thing to do) and asked my helper, "Is the mains off?"

"Yes, of course it is," came the reply but needless to say, it wasn't, as I rapidly found out. The taste of mains and saliva mixed is distinctly unpleasant, I can tell you.

Fuses can fool you

A 13-amp fuse in a 13-amp plug offers very little protection, whatever you may think. As Bill Launer, WB0CLD says, one of the most difficult concepts to grasp is that the basic purpose of a fuse (or circuit breaker) is to protect the wire or mains cable, not the equipment. In other words, fuses do not provide total equipment protection, only short circuit protection; if some degree of equipment protection is desired they will be selected to over-protect the electric wire.

A typical ‘fast-blow’ fuse will carry 135 per cent of rated current for up to 3,600 seconds before opening. It takes 300 per cent of rated current to cause instantaneous opening. A ‘slow-blow’ fuse will carry 135 per cent of rated current for up to 3,600 seconds before opening, and takes 300 per cent of rated current for 6 seconds (minimum) to cause instantaneous opening.

Since we normally put the fuses on the primary side of a power transformer (especially in HV supplies), and the output filters have large capacitors, which can act as nearly infinite current sources, you should never expect a fuse to protect you from shock (or worse!). Whilst the dangers of high voltage are well known, low voltage-high current power supplies can also be hazardous. You won't be shocked by 12 or 28 volts DC but you still need to be cautious and not wear rings or watches when you might get in contact with them – the resulting burns can be extremely nasty, as any telephone technician who has brushed his watch against the 50-volt busbar will tell you!

It hardly needs saying that people who replace fuses with higher values or with nails (they laughingly call these ‘supply stiffeners’) – or even bypass fuseholders and wire around them are not clever, just plain stupid.

Neon Screwdriver

The neon screwdriver is a cheap, simple and invaluable tool. Keeping one hand in your pocket, hold the screwdriver in the other and lightly touching the cap with one finger, bring the blade into contact with the chassis.  If the neon glows, the chassis is LIVE. You can check the neon by similarly touching the blade to a portion of the set which should be live, e.g. a tag on the mains dropper resistor (but it will not usually become lit if the chassis is LIVE instead).

Do remember that various receiver faults can render the chassis LIVE even if correct polarity is observed in the mains connection. Three common occurrences could be a bridged live pole on the mains switch, an open circuit neutral pole on the mains switch or even an open circuit neutral connection in the mains cable.  On sets fitted with fuses in each pole of the mains input, failure of one could render the chassis LIVE.

Work Area

If you are working with electricity and your work area has a concrete floor, a rubber mat is essential, particularly during damp weather! Where possible try to arrange a neat working area away from water or central heating pipes.  For safety try to arrange that this area is separate from the area occupied by your family. This is emphasised because inadvertently rushing to answer a telephone you might just leave a TV chassis connected to a supply and curious little fingers know nothing of the dangers of electricity - or, for that matter - the lethal vacuum encased within every picture tube!

Visual Inspection!

Before contemplating connecting any unknown receiver to the mains supply, spend a little time inspecting it for signs of missing or loose parts, blown fuses, overheating or even fire damage.  Use a meter to check obvious points to ensure no short circuit exists (e.g. across the mains input). If you then decide to apply power keep clear but be observant since an elderly electrolytic might explode!  This can be avoided if you can apply power gradually through a variac.  Auto-transformers are handy for supplying reduced power to sets being repaired but they are not a substitute for a proper isolation transformer!

Cathode Ray Tubes – storage and handling

Many younger enthusiasts may not be aware of the dangers of mishandling tubes, in particular the old round types found in early TVs. When handling these tubes eye protection should be worn and tubes must not be left lying around, they must be stored in boxes. The glass is surprising fragile and can implode without any provocation or warning. Bits of glass flying around at high speed can be deadly. The notes following are inspired by Malcolm Burrell again.

Picture tubes are perhaps one of the most hazardous items in any TV receiver.  This is because most are of glass construction and contain a very high vacuum.  If you measured the total area of glass in any picture tube then estimated the pressure of air upon it at 14.7lb. per square inch, you would discover that the total pressure upon the device could amount to several tons!  Fracturing the glass suddenly would result in an extremely rapid implosion such that fragments of glass, metal and toxic chemicals would be scattered over a wide area, probably causing injury to anyone in close proximity.  In modern workshops it is now a rule that protective goggles are worn when handling picture tubes.

The weakest point in most picture tubes is where the thin glass neck containing the electron gun is joined to the bowl.  It is therefore essential that you refrain from handling the tube by its neck alone. Once a tube is removed from the receiver hold it vertically with the neck uppermost and one hand beneath the screen with the other steadying the device by the neck.With larger devices it is sometimes easier to grip the peripheral of the screen with both hands.

Until the advent of reinforced picture tubes, most were mounted in the cabinet or on the TV chassis by some form of metal band clamped around the face.Never support the weight of the tube by this band since it has been known for the tube to slide out!  Some of the larger tubes are extremely heavy. It may, therefore, be easier to enlist assistance.

Before starting to remove a tube, first discharge the final anode connection to the chassis metalwork and preferably connect a shorting lead to this connection whilst you are working. It might be convenient to keep a spare piece of EHT cable with a crocodile clip at one end and a final anode connector at the other.

Exercise care when removing picture tubes from elderly equipment. You may find that the deflection coils have become stuck to the neck. It is extremely dangerous to use a screwdriver prise them away.  Gently heating with a hairdryer or soaking in methylated spirit is safer.

Disposal of picture tubes also requires care. Unless rendered safe they should never be placed in dustbins or skips. Many engineers swipe the necks off tubes in cavalier fashion using a broom handle but this is not recommended. A safer method is to make a hole in the side of a stout carton, preferably one designed to hold a picture tube. The tube is placed in the carton and the neck broken using a broom handle. The carton should then be clearly labelled that it contains chemicals and broken glass!

Mercury arc rectifiers

Most collectors are unlikely to handle these but they hold dangers. Handle them with extreme care;  they are often stored upside down and need to be turned over for installation. Upside down the mercury is in a narrow anode tube and doesn't slop around so much during transport (which should be in a sprung cradle inside a frame). Turn the tube very slowly so that the mercury moves slowly. The weight of the mercury is enough to crash through the glass if it moves with any speed. Not all tubes were made of UV-proof glass, so the light can contain large amounts of harmful ultra-violet rays.

Mains-Derived EHT

It is impossible to over-stress the dangers of mains-derived EHT systems found in pre-war and some early post-war sets. These systems are lethal, so treat them with respect. Unlike modern EHT systems, which are limited in the amount of current they can supply, these older systems using transformers straight off the mains can deliver enough current to kill an army. If you are not sure what you are doing, please ask a friendly colleague. For testing, use an EHT meter; they are still used by the TV servicing trade.

A few simple points will prolong your well-being. Keep one hand behind your back. This will prevent a shock across your body when testing. Don't laugh – a number of early TV engineers were electrocuted servicing these units. Note that the chain of 4.7megohms bleed resistors can go open circuit, leaving the capacitors fully charged after switch-off.

When starting work, switch off set. Remove mains plug. Discharge all EHT smoothing and, if fitted, reservoir capacitors by shorting them out with a 1k ohms resistor for 30 seconds and then by permanent links whilst working on the unit. Make up the links using plastic insulated rods, crocodile clips and probes. Do not come into contact with any part of the EHT circuit until you have carried out the above. Do not forget to remove all shorting links before applying power again. HVR2 and V16 valves are difficult to obtain!

Charged capacitors

Leaving charged-up electrolytics may be a legitimate prank in a shared workshop but it’s a recipe for disaster for forgetful ‘lone wolf’ repairers. You can discharge capacitors to earth with a screwdriver or a wire but the preferred method is to use a resistor built into a grounding lead with a test lead end on it. A 10K resistor works fine to reduce or eliminate the spark. Just be sure to hold it on for a second or three.

And yes, it was a favourite trick in old-time television workshops to toss a charged electrolytic to a colleague with the word “Catch!”. It’s a nasty trick because one’s natural reaction is to obey.

Noxious chemicals, fumes and common sense

Electricity is not the only hazard that lurks in the workshop. It’s funny (but only in an ironic kind of way) how many of the things we used to do are now considered highly dangerous. Remember the tin of paraffin or petrol in every workshop for cleaning grease and dirt off metal components... and good old ‘Carbon Tet’ (carbon tetrachloride) or ‘Trike’, the solvents that would get the muck out of everything. Naughty, naughty. We have to use safer methods these days.

But some of the chemicals that are still on the market are potentially lethal. The consumer magazine Which? has highlighted that paint and varnish removers such as Strypit (made by Rustins Ltd)  contain methylene dichloride (alias dichloromethane or DCM). This chemical is now listed as a Class Three carcinogen “with the possible risk of irreversible side effects”. As well as leading to nausea and drowsiness, it is a powerful skin irritant, meaning that you should wear rubber gloves and ensure good air ventilation when using these products. Better still, choose a non-toxic paint stripper.

If you must use  a chemical paint stripper or any other volatile chemical always use it out of doors to avoid breathing the harmful vapours. You don't notice it at the time but these fumes can make you feel really bad for three days afterwards if you're not careful. Current industrial safety regulations even limit the amount of soldering you can do in an unventilated room, so play safe. If you're handling acid, solvents or other noxious liquids, wear rubber gloves. They are not expensive and save a lot of pain, eczema, sores, and so on.

As Martin Ackroyd has said, the choice of paint stripper is easy: Sodium hydroxide (lye) merely causes burns that a good skin graft will soon put right. Methylene chloride destroys internal organs that are less easily replaced.

Oh yes... it’s awfully easy to ignore warnings about inhaling solder flux fumes or using powerful solvents such as xylene without wearing rubber gloves. Usually there are no immediate ill-effects and yet long-term exposure to low amounts is more of a problem than short term exposure to somewhat larger concentrations. The thing is to use common sense. Work outdoors, wash your hands well afterwards, use a simple dust mask if necessary, avoid certain materials completely, etc. You need have no worry about working with many toxic substances if you know what to expect before hand, and can plan your actions and safety measures accordingly.  Ignorance is what is really dangerous.

More traps for the unwary

Arden Allen points out that most, if not all, of the combined clean and lubricate preparations sold in aerosol cans have become more dangerous lately. That’s because the manufacturers are replacing the conveniently non-flammable chlorinated hydrocarbon solvents (that help destroy the ozone layer) with more environmentally-friendly flammable solvents. Read the label and look for the word Flammable.  Flammable liquids burn when they are heated to the point where they evaporate fast enough to produce a combustible mixture of gaseous fuel and oxygen (the flash point). When you add the third ingredient of the fire formula, namely heat, you’ve got problems, so don’t add the heat.

WD-40 is a typical example of these products and being a petroleum derivative, it is flammable (although its flash point is reasonably high and you need a pretty hot spark to ignite it). All the same, if you are using WD-40 to lubricate power switches, switch off the device first. Real fires have been started in this way. You can also start fires when certain switch cleaners (used for cleaning valve pins) soak into fibre or phenolic valve sockets if the cleaner has not had time to dry (being wet, it is conductive). Arden Allen advises that you cannot remove the ionic contamination out of the insulation once it is in. Even after you dry things out the insulation, being porous, it will absorb moisture from the atmosphere and eventually it will fail due to tracking and then arcing. You should clean sockets, etc., only with cleaners designed for cleaning electrical equipment. If you are in doubt about the condition of the insulation, saturate it with a moisture displacant, such as WD-40, then to avoid any risk of fire, allow WD-40 (which contains flammable solvent) to soak in and then dry for several hours before doing anything like throwing a high voltage switch or unplugging tubes while the set is powered up.

Some more nasties lurking in the workshop...

Mercury, which is poisonous, is used as a getter to absorb any remaining oxygen molecules in valves; this is what causes the internal silvering on some valves. There are also some old rectifiers that used mercury in them; when the tube is cold, you can see little drops of mercury adhering to the inside of the glass. In any case, be careful not to break any tubes that have little blobs of silver liquid clinging to the glass.

The risk of radioactivity is sometimes brought up and it should certainly not be ignored. Some USA-made common voltage regulator tubes had radioactive isotopes added, apparently to achieve more stable operation, whilst a number of WWII-vintage tubes (voltage regulators and radar T/R switches)  contain radium 226 in quite large amounts. Another source of radioactivity is the luminous paint containing radium used for dial markings on second world war radios, such as the British Army’s 19 Set. American military sets considered radioactive include:  ATD, BC-620, BC-654, BC-659, BC-1335, R-392, T-195, TBX and TBY.

Although post-war productions used a different, non-harmful luminous material, the original zinc sulphide and radium paint is now considered hazardous to health and according to one report, one type of ex-Royal Navy ship’s compass had to be recalled from the surplus market for this reason. Other equipment said likely to harbour radium paint includes the 18 Set, some domestic radios from the early 1950s with built-in clock/timers and American Jeep speedometers, also virtually all aircraft instruments through to the 1960s.

Radioactivity can even lurk in old hi-fi components. Sold at one time for turntable use was the Mercury Disc-Charger, a red plastic cylinder with a clip on its side, weighing half a gram, and a small metal  square plated with about 1 microcurie of radium-226 mounted in a shallow recess on the end.  It was very effective for neutralising static on records, and was used by simply clipping it onto the front of the  headshell. There was also a blue plastic teardrop-shaped version sold by a different company, but it contained a little less radium. 

A considered assessment of the risks arising from radioactive equipment is fairly reassuring, thankfully. The first issue is potential exposure to radioactive materials when using our radios; this can be termed the irradiation hazard. The second issue is the risk of accidental ingestion of radioactive materials; we can call this the contamination hazard.

In practice, the irradiation hazard from most radios is minimal; the radiation dose rate at normal operating distances will likely be barely discernible above background levels.  Good ventilation will minimise the hazard of inhaling radon gas given off by decaying radium.  The contamination issue is very different though.  There’s no cause for concern if the radium paint is inside a meter where you can't touch it, but if it is on  a front panel control, then a real possibility exists that you could wipe small amounts of radium off on your fingers, then eat or smoke, ingesting the radium. The same could happen if a tube containing radioactive material is broken. The small amount of material pose may not represent a significant health risk but it’s a risk that’s well worth avoiding.

With radioactive markings the best advice is to seal them with a coat or two of clear lacquer, to prevent picking up dust accidentally. They are easy to spot once you know what to look for, according to Lenox Carruth. Originally (and often on more recent equipment) the radium paint was light yellow in colour and appears thicker than the typical silk screened markings. Old stuff now looks brownish and no longer glows. If you clean equipment with radioactive markings, you should wear rubber gloves and dispose of all rags, paper towels and gloves afterwards, sealing them in a Ziploc polythene bag. Do not store radioactive equipment where it will be in close proximity to people for long periods.

Beryllium oxide (BeO) or beryllia, found in some power transistors, transistor and valve bases, VHF ‘ceramic’ transmitting triodes and klystrons, is very nasty stuff (if you inhale just a few micrograms, you could be dead in a week or two).  Luckily, if you avoid filing, sanding, or smashing the stuff, you are quite safe in handling it – large chunks are safe, micro-sized particles are dangerous.

Probably the best (and most obvious) advice is: don't put anything in your mouth; avoid handling broken glass, chemicals, or powders, using gloves when necessary; and work in a clean area with adequate light and ventilation.

Most of the 'ceramic' tubes and sockets encountered on amateur and commercial equipment do not contain BeO but the following Eimac/CPI tubes or sockets do contain it:

CV-8051, SK-3010, SK-3012, SK-3020, SK3040, SK-3060, SK3064, SK-3080, 4CS250R, Y621B and some Klystrodes, also certain power transistors.

BeO can also be found in the Signal One CX7 receiver and in some commercial amplifiers. But why all the fuss? Easy - the dust is extremely toxic when inhaled. It sets up an inflammatory reaction in the lungs. This leads to progressive pulmonary fibrosis where the lungs scar up and lose the sponginess essential to their function, and then you die of slow suffocation.  A minute amount is enough to trigger the process and there is precious little treatment short of lung transplantation.

Although there is no easy way to determine for certain if something is made of beryllia, it is not toxic just sitting there doing its job. You can't tell whether the hard, white material is alumina (aluminum oxide, unglazed ceramic, steatite, etc.) or beryllia just by looking at it. But you can be aware of where you might encounter it and take precautions with all the hard white materials that you may encounter. As Arden Allen points out, it is only toxic if you ingest it or breathe dust after grinding it.

Lithium is found, not surprisingly, in the Lithium batteries in some more recent equipment and after a number of years these cells are frequently found leaking. Lithium is pretty nasty stuff and these batteries should be removed and disposed of thoughtfully. Cadmium, from plating, should also be treated carefully, especially when wire-brushing corroded parts. The dust is far too easily inhaled - or ingested with food if you forget to wash your hands.

Oil-Filled Transformers and Capacitors

Many oil products are considered harmful if misused; some engine oils are carcinogenic and should not be allowed into contact with your skin. Other types, containing PCBs or Poly Chlorinated Biphenols, are deadly if allowed to overheat and vaporise. Older television sets contained many oil-filled products –  high-voltage capacitors,  transformers found in  and EHT triplers in projection sets – and these may contain PCBs. If these do not leak or overheat you have nothing to worry about but you should be aware that environmentalists are extremely concerned about PCBs. Their use is banned in most situations nowadays and there are strict rules governing the disposal of products containing PCBs. To avoid the risk of skin cancer and other things too horrible to mention, wear rubber gloves when handling oil-filled devices and  read these handling instructions. You have been warned.

Selenium rectifiers

Selenium dioxide is the major compound produced when a selenium rectifier is overheated.  It can cause severe burns to the mucous membranes and severe respiratory tract, skin, and eye irritation.  It can also promote allergic reactions with the skin.  Fortunately it is not considered a carcinogen. 

Another fortunate thing is the awful smell which gives it away.  If you smell something really rotten, like decaying onions and garlic, coming from your equipment, it is best to leave the area immediately, opening some windows on the way out.  Allow the selenium dioxide vapours to dissipate for several days before you go back - you will not want to go back very soon anyway! 

Explosive charges

This, fortunately, is a low risk but still a real one. Military radio and radar equipment made during World War II, in particular by the Americans and Germans, was sometimes fitted with explosive charges. These were intended to destroy the equipment in the case of accident (impact) or capture by the enemy (tampering). In recent years at least one collector has seen his garden shed go up with a bang (spontaneous detonation) and another, to his horror, had an innocent-looking ‘component’ identified as a charge. Frequently these detonators look extremely similar in shape and size to electrolytic capacitors and issue 117 (1998) of Funkgeschichte, the German historical wireless society’s magazine, has photographs which illustrate this similarity well. It also quotes a newspaper report of 1949 in which a domestic radio technician testing war-surplus radio components for re-use lost his sight when one of these ‘capacitors’ blew up in his face. In the Australian electronics magazine Radio, Television & Hobbies (later renamed Electronic Australia was a similar warning about the dangers of old demolition charges in wartime eqpt. An Australian radio ham was injured in Melbourne when modifying an old aircraft radar unit that he had picked up in a surplus shop. He attempted to bench test a 'capacitor' and got badly cut and burnt hands plus metal fragments in his face.  He was lucky not to lose his sight.

Times change

Old technology, as we said at the outset, is not intrinsically safer than today's equipment, neither can we take satisfaction in old-fashioned attitudes to safety. If you peruse F.J. Camm's Hobbies New Annual for 1937 you'll find tantalising projects such as  'Fun with Photo-cells' and 'The Genet Midget Three Valve Wireless Receiver'. But just take a look at his experimental descriptions, for instance:

'Just cover the quicksilver with some dilute sulphuric acid (accumulator acid will do) in which a few crystals of permanganate of potash have been dissolved.'

This  makes our safety-conscious age seem rather tame, doesn't it!

Another header reads:

IGNITING, PETROL, GUNPOWDER, ETC.

and warns:

'sometimes the experiment is rather violent, the substance blowing up rather than burning'.

This sort of thing is priceless and may amuse us today. Life was obviously cheaper then.

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