Wireless Sets and the Vehicle Collector©


By Major (ret’d) David Lawrence, CD


Copyright © 


            Some would say that a finely restored military vehicle is nothing more than a convenient way of transporting a finely restored military radio.  I would heartily agree! 


Well, what would you expect from someone who has lots of wireless sets but can only dream about owning a Dingo?  Nonetheless, there may be something to be learned from someone who is an “outsider” to the vehicle collectors’ fraternity.  This article outlines some issues that should be considered by a vehicle collector when dealing with military wireless sets.


  There are three main areas to consider: the potential for damage to the radio, the potential for damage to the vehicle and the potential for interference with other users.  While many of the comments relate specifically to the Wireless Set No.19 or the C42 Set, the points are generally applicable to all wireless sets.  (Editor's Note: Also see "Radioactive Hazards of Vintage Radios", at bottom of this page.)


            If the goal is to restore a vehicle to running condition, it is also reasonable to try and restore the radio.  While it is certainly possible to make vintage wireless set operational, there are hazards – mainly due to fire and/or explosion.  Fire is fairly rare but usually destroys the inside of the set beyond repair.  Explosions are fairly common and generally easy to clean up. 


The components that usually fail are the capacitors – especially the big ones in the power supply.  These are made of two large sheets of tin foil separated by a thin layer of paper which is soaked in an electrolytic material.  These sheets are rolled, electrodes are attached and the entire assembly is sealed in an aluminum can.  When power is applied, a very thin layer of oxide forms on the foil plates and insulates them from each other. 


However, with age, the electrolyte can dry out, resulting in an imperfect layer of insulation.  When power is applied to such a capacitor, there is a significant current through the component which results in heat.  This creates pressure which increases inside the sealed can until it “fails”.  The failure of a power supply capacitor in a 19 Set is roughly equivalent to the discharge of a 12 gauge shotgun in a telephone booth.  For any ex-gunners who fail to hear the noise, the large cloud of white smoke will be the second clue to the failure. 


There are 118 capacitors in a 19 Set of which 46 have the potential to fail catastrophically.  However, “less than catastrophic” failures of capacitors are also of concern.  A leaky capacitor does not perform its by-pass function properly and will often cause a shift in the bias voltages of the vacuum tubes.  This causes the set to perform badly - if it works at all.  This same symptom can result from a shift, due to aging, in values of the 102 resistors in a 19 Set.


            Power can certainly be applied to an old wireless set but it needs to be done cautiously.  The power supply capacitors should be electrically isolated from the rest of the circuit and then monitored for leakage as the voltage across them is gradually increased.  By this process, it is sometimes possible to fully restore the insulating qualities of the capacitor.  Depending upon the condition of the component, this can take from one hour to several days. 


Success, however, is not guaranteed.  It is possible to get an estimation of the quality of the remaining capacitors by gradually applying B+ voltages to the set (usually 90 to 600 volts depending on the set).  As this voltage is increased, the current drawn will momentarily increase (while the capacitors charge) and then drop back to a lower value.  If the current does not drop back, or if it begins to rise without the voltage being increased, this indicates that a capacitor is about to fail catastrophically.  Power should be removed from the set immediately!  If these initial checks are successful, it is possible that the set is operable without massive restoration work.


            The best way to avoid having to replace all the resistors and capacitors in a set is to totally avoid any set that appears to have been badly stored.  Clues to this can only be found by looking inside.  For a 19 Set, this requires removal of the transmitter/receiver from its case and removal of the bottom plate.  Look for any modifications to the set (usually fairly obvious) as well as any signs of dirt, moisture and “living things”. 


One of the best indicators as to the set’s storage environment is the condition of the conformal coating on the inductors (coils of fine wire).  Poor storage conditions will cause the coating to be cracked, brittle and flaking.  Such sets may present significant restoration difficulties.  Both the top and bottom of the chassis should be clean.  If the top is dirty, it suggests that the set has been stored outside of its case which would have likely exposed the components to much more environmental stress than would be desirable.  If the set has been modified in any way, and if those modifications are not fully documented, restoration may be difficult.  Such sets may be useful for parts. 


For a C42 Set, if it has not been removed from the case, it is likely to be very clean inside.  Alternatively, water may have entered through the seals but then been unable to drain.  This is a disaster for a wireless set and the evidence of water damage will be obvious.  For such a set, with the addition of 50 feet of rope, a C42 set makes a fine anchor for a small boat.  It will be of little practical use for any other purpose.


            So, to summarize, purchase only sets in good condition, apply power carefully, wear safety glasses and don’t be startled by loud noises and smoke.


            The second area of concern is the potential for the wireless set to damage the vehicle.  Aside from the obvious hazard of the set itself catching fire, there should be a concern about batteries and about the wiring in the vehicle.


            Most large sets (e.g. 19 Set and C42 Sets) run from either vehicle power or separate lead-acid storage batteries.  The electrolyte in these batteries can ruin both the set and the vehicle in a very short time (i.e. minutes).  It is highly recommended that such batteries be removed from the vehicle unless the set is actually in use.  Since it is virtually impossible to find original batteries for these sets, some modern alternative must be used. 


For large sets, a deep-cycle battery is the only practical choice.  These batteries are designed to supply about three-quarters of their rated capacity without ill effect.  Regular car batteries will not survive such service.  Car batteries are designed to give a very large current for a very brief period of time and then be recharged immediately.  Their plate structure is simply not robust enough for use with wireless set.  It is far more economical, even in the short term, to purchase deep-cycle batteries.


            All power supplies must be properly fused to prevent damage to the supply, the set and the vehicle wiring.  For larger set, especially those operating from vehicle power, it is crucial that both the negative and positive leads be fused as near the battery as possible.  These fuses should be of the “slow-blow” variety, as the instantaneous starting current for the 12 Volt dynamotor power supply in a 19 Set is very high - often in excess of 50 Amps.  Running current is much less – usually around 12 Amps.  A “slow-blow” rating of 15 to 20 Amps is usually sufficient. 


Of course, the vehicle wiring must be capable of carrying such currents without excessive voltage loss or heating.  The reason for fusing both leads is to prevent potentially damaging ground loops.  If the negative lead were not fused, and the connection from the vehicle battery’s negative lead to the vehicle’s ground was not perfect, then any current being drawn from the battery would find its return path through the wireless set’s negative lead.  This will cause arcing where the set contacts the vehicle chassis and cause erratic operation of the vehicle’s electrical system (particularly the lights and starter motor).  If this battery connection to the vehicle is poor, it is better to have the fuse in the radio’s negative lead blow, correctly identify the problem and clean the battery connection before more serious damage is done.


            When vintage sets are being powered from the vehicles charging system, attention must be paid to the input voltage.  At normal cruising speeds, this is often in excess of 14 (or 28) volts.  With a 19 Set, such voltages will make the dynamotor run faster than normal and cause it to produce significantly higher than normal voltages.  This puts a considerable strain on the components, especially those in the power supply.  Having the filter capacitor fail while you are driving down the road is likely to be highly distracting!  With the C42 Set, there is a voltage sensor in one of the control boxes.  This adds a series resistor if the supply voltage rises beyond 25.5 Volts.  This arrangement allows a C42 set to operate properly with an input voltage range of 20.7 Volts to 29.0 Volts.  Nonetheless, it is prudent to be absolutely certain that the vehicle charging system is working properly before connecting a wireless set.


            Interference from the vehicle’s electrical system can be strong enough to completely blank out radio signals.  Poorly shielded ignition wires or bad brushes in the generator are often the culprit.  Another common cause of interference is poor electrical bonding amongst the body parts, especially the “bonnet”.  The use of shielded ignition wires was very common in vintage military vehicles, specifically to minimize interference.  This is even standard on the little Chore Horse generator used to recharge wireless set batteries.  To successfully operate a wireless set, especially on the short-wave bands, it will be necessary to minimize any electrical interference from the vehicle.


            Finally, we come to the big question, “Can I put it on the air?”  The short answer is, “no”.  The long answer is, “maybe”.  The Radiocommunications Act, Section 4 is paraphrased as follows: “No person shall, except with a radio authorization, install, operate or possess radio apparatus”. 


The term “radio authorization” means having both a certificate of proficiency for the person using the set and a station licence for the actual device.  The term “radio apparatus” means a device intended for, or capable of being used for, radio communications.  The punishment for contravention of this section is a fine of up to $5,000 and/or imprisonment for a term not exceeding one year.  To be clear, if you own a wireless set and you do not have a radio authorization, you have already committed an offence


Unless you are a commercial or military user, the only way to legally own or operate a transmitter in Canada is by being an Amateur Radio Operator.  To obtain such a qualification requires successful completion of a test covering technical matters, operating procedures and Radiocommunications Act regulations.  To operate on the short-wave bands (i.e. where most British WWII sets operate), you no longer have to demonstrate any proficiency in Morse code.  The level of knowledge required for the basic licence is easily within reach of most technically minded individuals.


            While the above restrictions might seem unnecessary when applied to a low power, vintage wireless set, practical experience suggests otherwise.  A 19 Set puts out about 15 Watts of radio frequency energy at up to 8 MHz.  Several members of the Wireless Set No. 19 Group have completed trans-Atlantic contacts with these sets.  In fact, it has even been done with a 22 Set which has only one and one-half watts output!  While these contacts are not the norm, they are entirely possible, even predictable, with the proper selection of antennae and operating times.  If a wireless set is not installed and tuned properly, it will produce spurious outputs at higher frequencies.  These higher frequencies propagate further, and with less power than the lower frequencies.  Both the intended and spurious outputs from these vintage sets can interfere with other users of the electro-magnetic spectrum.  These users include commercial operators, military forces and trans-oceanic Air Traffic Control (ATC). 


Be assured that if two 19 Sets are capable of maintaining communications between Kingston, Ontario and Oslo, Norway; they are fully capable of causing significant interference to trans-Atlantic ATC.  Likewise, the C42 set can generate spurious signals on aircraft navigation and communications frequencies.    In the post 9/11 environment, it would be unwise in the extreme to attempt to operate a wireless set without knowing exactly what you are doing.  Both Industry Canada and various military organizations have direction finding capabilities that are astonishing in their accuracy and speed.  Any interference with the use of the radio spectrum, especially to frequencies used by aircraft, is treated as extremely serious.


            As a minor point, the whip antenna used on most vehicles is the most likely type of antenna to cause long range interference.  During WWII, most British wireless sets operated via “ground wave”.  This required that the signal be transmitted at as low a radiation angle as possible (i.e. right at the horizon).  This is the primary characteristic of the vertical antenna.  With ground wave, however, the signal is attenuated as it passes over the ground until it disappears in the noise. 


With 19 Sets it has been possible to work over a distance of thirty kilometers in ground-wave using only a twelve-foot whip.  With the thirty-four-foot mast as an antenna, 19 Set signals have been copied at over 100 kilometers.  This is considered the extreme range of 19 Set when using ground-wave propagation.  If a horizontal dipole antenna is use, the signal is radiated in a more vertical direction towards the ionosphere.  This signal is refracted and comes back to earth at some distance.  Using this “sky-wave” mode of propagation, 19 Set communications at distances of 500 kilometers are the norm and distances of 1,200 kilometers are common.  For really long distance communications, the best mode of propagation is to use sky-wave but with very low angles of radiation. 


This is exactly what results when whip antennae are used.  So, depending upon terrain, local noise levels and a great many other variables, it is entirely possible to be out of contact with another 19 Set at relatively short distances, but to be in solid communications at extreme distances.  In this way, it is possible for some local experiments to be unknowingly causing significant interference at great distances.  Again, the same caution applies to the use of the C42 set.  Harmonics from this set can interfere with aircraft navigation receivers at a distance of up to 150 km (depending on the altitude of the aircraft).  It would be indeed unfortunate if what seemed to be a “harmless experiment” resulted in a commercial airliner straying outside of its ATC corridor or having its Instrument Landing System (ILS) approach compromised..  


            It may seem that the above paragraphs are intended to scare a military vehicle collector from every turning on a vintage wireless set.  This is only partly true.  With the necessary technical background, test equipment and appropriate licences; vintage wireless sets can be as much fun to operate as vintage vehicles.  Operating without that necessary background, however, would be like attempting to drive a White Half-Track across the top of Toronto during rush hour.  You would likely survive but a lot of others might not.


            So, what can a vehicle collector reasonably do with vintage wireless set?  If the set is working, it is easy to configure it in a “receive only” mode by disabling the transmitter.  This can be done by disconnecting the wire that provides power to the transmit/receive relay and/or removing the transmitting tubes.  This latter measure has the additional advantage of reducing the power consumption of the set.  With the 19 Set, pulling the brushes from the HT2 section of the dynamotor will keep the 550 volts out of the transmitter altogether and reduce the stress on the set.  With the removal of a few components (all of which could be easily reinstalled) the power consumption of a 19 Set can be reduced below three Amps.  This makes it ideal for display purposes where the receiver can be set to pick-up either the BBC World Service or the time signal.  In such a configuration, it is unlikely that a collector would draw any unwanted attention to a wireless set for which he might not have all of the appropriate authorizations. 


An added advantage to disabling the transmitter is that the danger of radio frequency (RF) burns is eliminated.  Even at relatively low power levels, the RF voltages on an antenna can be significant (200 Volts at the top of a 19 Set’s 12 foot whip).  If a member of the public were to have his hand on the antenna at the same time as someone inadvertently keyed the transmitter, a nasty shock would result.  It is better to avoid such a possibility by simply disabling the transmitter. 


            If it was necessary to have a fully operational set for re-enactment purposes, then two options exist.  The first is to become qualified as an Amateur Radio Operator.  This is the best option but maybe not the most practicable.  The second option is to get a “junker” radio, gut it and install a 27 MHz CB set inside.  This has several advantages.  First, it is legal as CB sets are now unlicenced in Canada.  Secondly, it is relatively easy for the non-specialist to interface the vehicle’s control boxes to a CB set (requires only audio out, audio in and push-to-talk connections).  Finally, the ideal whip antenna for a 27 MHz CB set is about nine feet long.  This is very close to that used on WWII wireless sets and should give a range of about eight kilometers.  Also, these frequencies (and their harmonics) are not easily refracted by the ionosphere and therefore are unlikely to cause any interference with other users.  It is not often that the cheapest solution is also the simplest and entirely legal!


            Hopefully, vehicle collectors will have found the above comments useful.  In the quest to have vehicles that are perfectly restored, a wireless set is a wonderful addition.  Having it do more than just look pretty is a bonus that is easily achievable.  All that is required is a little bit of knowledge (often a dangerous thing), some patience (sometimes in short supply) and a desire to take the necessary steps to avoid a number of potential problems.


            For any collectors in Southern Ontario, look for members of the Wireless Set No. 19 Group at the militaria shows.  For those with web access, the Group’s website contains a lot of useful information (http://www.qsl.net/ve3bdb).          




About the author:   After graduating from Ryerson Polytechnical Institute in 1971, David Lawrence worked in the electronics industry for four years.  This was followed by twenty-one years service as a Communications & Electronics Officer in the Canadian Forces.  He holds an Advanced Level Amateur Radio Licence (call sign VA3ORP) and is one of the founding members of the Wireless Set No. 19 Group.  As a volunteer, he has worked at both the Military Communications & Electronics Museum and at Fort Henry National Historic Site.  He is currently a part-time student at the Royal Military College of Canada where he is pursuing a Bachelor of Military Arts and Science degree.



This article is protected by Copyright © and must not be copied, transmitted, published or displayed elsewhere, in any manner or form whatsoever, other than brief passages for review purposes only, without written permission.  In the latter case, credit must be given to the author and to the Wireless Set No. 19 Group website.  Failure to abide by this notice may be actionable at law.  Please see Home Page for full Copyright information.



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