Refurbishment of an old Field Phone

 I have two old First World War field phones which are basically identical and came from a farmer who discovered them in a barn. From the extremely poor condition I suspect they may have been intended for use perhaps between farm buildings nearly a century ago, being the sort of things sold as government surplus in the early 1920s, needing only a couple of bell batteries and a length of cable to make them usable. For some reason the things had been ditched and left to deteriorate. Woodworm had eaten them and they'd ended up in a very sorry state. Because of this I paid very little for them. After many years I decided to rebuild the phones in new boxes, but after some consideration, in order to keep their originality, I decided to restore at least one by treating the worm-eaten wood by stabilising and filling it. The first steps were to photograph the thing in its original condition and then to remove all the parts so I could restore the woodwork. In case the original label became damaged during repair of the lid I produced a new one but adding a section to the top right that was missing on the original and of course disguising woodworm holes in the paper of which there were plenty....



 Above is probably one of the worst affected areas and will need a new piece of pine grafting in. There are traces of filler dating back decades. Below, the exterior of this section isn't too bad although the wood itself is almost entirely eaten away. The woodworm clearly didn't like the taste of the brown paint especially under the metal plate.


 Below you can see a brass terminal. These are 2BA and fitted into the woodwork using a slotted circular nut embedded in the wood. The outer hole was then filled with pitch. There are three such terminals and one had completely seized. This would have been one of the battery terminals and became badly corroded due to a flat battery. See later. Connections from the phone circuitry to the terminal posts were made by thin wires sealed into the wood. The slot on the left is where the telephone handset socket was mounted. The large hole is for the magneto. The interior finish looks OK but is just a thin layer of varnish over a virtually hollow interior.





 That centre panel looks OK but is almost hollow and very fragile and as you can see dust falls out of the holes whenever it's moved. The worms didn't fancy eating the varnish and remained inside the wood until emerging from their holes in search of another meal.

Below the model number of the phone punched into the wood.



 Below, there's evidence of a filler when the woodworm damage was probably minimal. I needed to cut through the filler to access the hard resin used to fill holes where screws fitted to secure the parts.




Above you can see where wood has been eaten away leaving only a thin layer of varnish.

The next three pictures show the sliding lid with its thick layer of paint. In order to harden the wood the paint needed to be removed and underneath you can see the honeycombed remains looking more like a Ryvita biscuit than a piece of pine.



 To repair the wood needs a hardener followed by a wood filler. As the box has grooves into which the edges of the lid fit I made a frame to hold the rotten section in place when the filler is applied. This fits over the tongues at the edges of the lid.


 This section is hinged to the top of the box and because one hinge had seized the corner of the wood had broken off. The best way of tackling this repair is to cut away the corner to straighten the edges so a new piece of pine can be fitted into place. This is a technique known as "scarfing" and is frequently used when repairing rotten window frames.


The texture of the wood can be seen here. Most of the box is like this making it very fragile. Again, I made a frame so that the repair could be made without further damage.



 In order to tackle the repairs to the woodwork I needed to remove all the internal parts. Many of the interconnections are made using small metal strips having tapped 6BA screws. These strips are fixed to the case with tiny countersunk wood screws.

Below is the largest of the parts, the magneto.



 Now the buzzer which carries the clapper for the bell.


   This is a metal plate that fits in a slot at the side of the magneto. It looks like mu-metal.


 The part is a transformer termed "COIL INDn. No.1" and carried a small metal plate at its end, again looking like a pece of mu-metal. The coil was very difficult to remove because the securing screws had rusted and jammed in the holes.



Below, a couple of views of the bell. In this model phone only a single bell is fitted.






 Another view of the handset jack plug. The lower pin is corroded because it connects to the battery and once a battery degrades sufficiently there's a transfer of metal between ends of a connecting wire of metal-metal junction. You see this effect if you leave flat batteries in a flashlight.






Below the phonetic alphabet plate. This is slightly unusual as it has "AC" rather than "ACK".



 Here are some of the parts from above derusted and painted.


 Now some pictures of the wooden parts being restored. The first is the worst side of the box where the top left section was missing, being attached to a seized hinge and the bottom section which had been mostly eaten away. Someone has previously applied a grey filler and I'd guess this area was the first to get infested. I squared up the two missing areas to make it easier to patch them. The lower area is made of two new pieces of wood of which the larger makes up the basic size and the second jammed in place to fill the gap once surrounding material had been hardened. A third piece of wood will be fitted later to accommodate the hinges. The picture below this one shows further work including filling worm holes. The white glue will harden and dry to a transparent finish



 A rear view of the wood insert shown above-right. This insert is placed and glued to the inside of the remaining varnish mainly left in place. I cut the groove for the sliding lid once the insert was solidly in place. The wood inserts need to be clamped in place until the glue hardens, and to minimise leakage of the glue I applied paper between the clamp and the box. Many of the surfaces which look to be in good order in fact are merely just a layer of varnish with no wood underneath. In several of these instances I made a slit in the surface of the varnish with a knife and fed glue into the cavity to stabilise the wood.


 The plan is to use a final coat of wood filler to make good the various holes, then to sand this flat. I'll finish the outside of the box with a grey flattening primer which should result in a smooth matt finish, preparatory to painting. The inside surfaces are varnished. Below is the outer surface of the lid which was extremely fragile and now hardened ready for wood filler.



 A third patched area, this being on the lower lid. The damage was to the wood carrying the seized hinge which had torn away. The repair was done using two wood inserts to preserve the shape of the corner without cutting away too much original material.

Below, an outer surface in reasonable condition except for scores of woodworm holes. The white glue will change to a transparent finish once hardened and can then be sanded before painting. The right hand edge fits against the hinged lower lid. The left edge carries grooves on the inner surface for the upper sliding lid. Impressed at the centre is the phone's model number and there are further identifying numbers at the bottom left, which should all be present after refurbishment has been completed..


 Below, a third piece of wood was needed to set the hinges in place. These are fitted flat against the lid and countersunk into the end section with a slight taper to the wood below the edges.


 Having got this far I tackled the job of filling the damaged areas too small to replace with wood. I used a wood filler that came in two parts and found that you had to apply the filler fairly quickly and to not try to be too careful to get a first-time perfect finish otherwise the filler had started to set and dragged off making matters worse. The job was carried out in three stages. The main filling task, smoothing with a coarse sandpaper, then a final application of filler to re-instate edges of the wood and fill remaining woodworm holes.








 It became apparent as work proceeded that the final aim should be to let the phone show its age.

The final finish will be in a brown paint fairly close to the original which had plenty of brush marks so a spray paint is not ideal. The pictures above show various views of the box with the hinged top painted in a grey spray-on primer which later I swapped to a white brushed primer to match the wood filler colour.


 I chose Dulux Dorian in dead flat matt for the new paint. The stuff came in a small plastic pot with a screw-on lid. The colour rendering in the photos was tricky to reproduce so won't be exactly true-to-life but the end result does look like a WW1 shade of khaki.


 The internal finish is a varnish with a lot more colour than the original as I needed to mask the fillers. Ideally I should have colourised the filler but as it set very rapidly that option would have been tricky.


 During the restoration process spilling of wood dust was a problem. Most of the wood content of the box was converted to dust which was lodged in a honeycomb of harder grain and outer paint and varnish. The weight of the case is probably about half that of the original.


  I believe these phones were protected by a canvas cover such as the one shown in the high voltage unit I have elsewhere in the museum.

For reference I've added a photo of a spark transmitter HT unit of the same vintage below.


 The lid below slides into place in grooves and allows access to the handset, whilst the other lid is hinged to the rear of the case. A brass screw is used to hold it closed. Earlier versions use a brass catch which must have been relatively expensive to produce so was later eliminated. This later example is missing the catch so the outer case and the lid each have a wooden patch in its place with the lid relying on friction and the canvas cover to keep it closed.



 The old labels are in a bit of a mess. I initially planned to leave the better example but replace the other with a facsimile, but eventually replaced both.




 Before refitting the old block condenser I decided to check it with my ESR meter. As you can see from the markings it's rated at 2uF and the test revealed it was still very close to the original value and at 5.1 ohms is remarkable for its age which is over 100 years. The other markings are "W.D", "No.3" and "4015".


Below are pictures of the phone after most of the reassembly. I need to add a few termination strips and finish the wiring. I had a little difficulty getting the colour balance of the photographs right (possibly because of the filter I used), but the final result looks really authentic for a First World War equipment. I used a small 236cc pot of Valspar "Dorian" dead flat matt paint.


 The original box had a pitch used to fill the various holes (above are holes locating the securing screws for the magneto.

To avoid over-cleaning the metal fittings and removing their patina, I used a fibre pen sold for cleaning circuit boards. This removed verdigris but left most of the patina.

 Below, most of the parts are refitted but wiring is unfinished and there's a large terminal to be screwed into the wall of the battery compartment together with battery leads etc.


 In most of the interior the finish was just a thin film of varnish with no wood left beneath it.








 The worst section of the box, the rear panel, showing the stages in its repair. Rather than scrap the entire side I kept as much as possible of the original wood even though it was in pretty poor condition and very fragile until treated with a wood hardener. By doing this I was able to keep most of the jointing between the pieces which gives much WW1 equipment its unique character.

The screws are used to mount the magneto in the box and the holes were originally filled with pitch.






I didn't want to use a wood filler to make the outer surfaces completely smooth and which would change the character of the interior so it took lots of coats of varnish to seal woodworm holes. There's still a lot of dust falling from the surfaces because of this.






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