Wireless Set No. 52 Canadian - Project

[David Dunlop]

Step 3 in the removal of the Coil chassis assembly from its case is to remove from the bottom, the three screws that have washers, pictured at the end of the last post.

It was a little disconcerting to see that whoever last fitted this hardware to the case had run these three screws down so hard, the flat washers had cut into the pine board so hard the outer faces of the washers were actually flush with the surface of the board and the wood was coned inward noticably around each of the three screws. Note the first two photos. the concern here was that the base of the coil assembly these three screws are securing to the bottom of the case, is not metal. Rather, it is a mere 1/4-inch plate of brown phenolic resin. There was a very real possibility the overtightened screws could have torqued the threads they cut in the resin so much that the threads would simply strip out of the holes when these screws were removed. Fortunately, all three screws came out smoothly and there was no sign of resin dust or particles stuck to the screws. These cones in the wood will have to be filled in and levelled, and the flat washers carefully re-flattened when reassembly takes place.

The three chassis mounting screws are 3/4-inch, RH, slotted self-tapping machine screws with a 1/8-inch diameter shank and a 20 thread pitch. I have run across 1/4-inch long versions of these screws in wireless equipment over the years which have a small V-shaped notch at the tip. These longer screws do not have that notch for some reason. The threads just run out about 1/16-inch from the tip.

The flat washers are 3/8-inch OD with a 1/8-inch diameter centred hole.

At this point, the coil chassis assembly is only secured by six screws around the perimeter of the front panel. These six screws thread into six small steel brackets fitted around the inner edge of the case, each bracket held in place by a pair of small machine screws and hex nuts. See the last photo of my Parts Coil to get an idea where the last removal step is headed.


David

[David Dunlop]

As noted, with the removal of the required six screws from the front panel of the Coil chassis assembly, it is now ready to be removed from its case. The first photo here shows these six screws removed. These screws are a zinc, or cadmium, plated 8-32 x 3/8-inch RH slotted machine screws.

The designers at Canadian Marconi Company seem to have thought of everything with the 52-Set. The coil chassis is quite heavy and rests on a large plate of 1/4-inch brown phenolic resin. This is an important insulator for the coil assembly and can be damaged, so the designers added a sheet of green felt to the bottom to the Coil Case for the chassis to rest on and this also makes it quite easy to slide the chassis in and out of the case.

To extract the chassis from the case, it must be slid forward to release the front panel from its recess. this requires a forward movement of 1/4-inch. The safest place to push the chassis forward is to place a finger on each bottom corner of the phenolic resin chassis plates where the side and bottom plates meet at the rear of the assembly. See the second photograph. Apply equal pressure to both sides and push slowly.

Remember that bottom central bracket I pointed out earlier that the front panel is secured to, in Post #1093? The one with the gap cut out in the resin plate around it? The gap behind the bracket and the bottom resin chassis plate happens to be 1/4-inch. When the resin bottom plate hits this bracket, the lower edge of the front panel will have just cleared the lower lip of the wooden case and will drop down just enough to allow the top edge of the front panel to tip away from the upper lip of the case. You can then put your fingers under the lower edge of the front panel and lift it all up enough for the bottom phenolic plate of the coil chassis to pass over the bracket and you can carefully slide the entire chassis assembly out of the case.

The third photograph shows the green, felt pad clearly in the now empty case and the last photograph shows the Coil chassis assembly now sitting on its own.

Time for a glass of wine.


David

[David Dunlop]

Well the first discovery about this Coil assembly with it finally out on the bench for a closer look, was a very positive one.

What looked like a very odd oxidation on the brass gear set for the coil tuning turned out to be a very nice distribution of a medium weight grease which was in excellent condition. Probably applied back in the 1966 Workshop overhaul for the set. The grease shall stay. It has earned its place.


David

[David Dunlop]

The design of the Coil, Aerial Tuning No. 2 A is slowly revealing itself, in spite of not much being said about it in the documentation for the 52-Set. The only technical references it gets are that it is not to be used at all above 10 Mcs and the Sender is to be connected directly to the aerial in use, and, that it is fully interchangeable with the Coil, Aerial Tuning No. 2, issued with the Wireless Set No. 9 Mk I Cdn.

One thing that has now surprised me, because I have missed it for several years now, is that the front panel for the Coil is cut from 1/8-inch Aluminum plate whereas all the other components in the 52-Set have front panels cut from 1/16-inch sheet steel. I am glad I now found this out as I have no primer for working with aluminum when it comes time to repaint the Coil front panel. That product is now on my ‘To Be Purchased’ list.


David

[David Dunlop]

While inspecting the Coil I am using for the 52-Set, I found ‘3978’ stamped in blue ink on the bottom side of the phenolic resin base of the coil chassis itself. I then found the same number stamped on the outer surfaces of the resin left and right side panels. See the first three photos. I am thinking this might be a Production Control Number used by Canadian Marconi Company during the manufacture of these coils, in a similar manner to the hand written four digit numbers found on the inside chassis surfaces of the other set components. The only other stamped marking I have found so far is the part number for the coil itself, CMC 119-521, which was stamped along the left side edge of the coil drum as shown in the last photo.

Now I have to see what I can find on the parts coil assembly.


David

[David Dunlop]

My parts coil revealed the number ‘8798’ stamped on the same parts as the four digit number that was found on the Coil assembly for the 52-Set, as per the first three photos.

The main difference was the Part Number for the Coil itself was not along the left edge of the drum, but now located on the left side plate of the drum. See last photo.

So if these numbers are indeed Production Control Numbers, then this Coil assembly came down the line a lot later than the first one. Is the new location for the coil Part Number as production change for some reason, or just a fluke?



David

[David Dunlop]

For such a small, and electronically simple component of the 52-Set, this coil assembly holds an amazing number of mysteries for me and they just keep popping up!

In fairness to the Engineers and Designers at Canadian Marconi Company 80 years ago, a fair bit of these mysteries are probably directly related to my limited practical and theoretical electronic knowledge related to this calibre of wartime wireless equipment.

The first, and still current mystery, revolves around the existence of the small cylinders found mounted just below the tuning gear drive assemblies on the right side plate of the coil chassis as per the first photo. They are not physically connected to any circuit in the entire coil case, just the 1/4-inch resin side plate. My first thought was they contained a coil intended to balance out the presence of the large mass of metal present with the tuning gear drive next to it.

Last night, however, I discovered these cylinders are not hollow. The ends of the two I have available to study finally revealed they are a tight roll of resin impregnated fabric. It is still possible that a very fine weave of non-ferrous mesh, or foil, is wrapped up within the coils of fabric, and these cylinders are serving some form of electronic purpose.

A new ‘longshot’ idea is these cylinders are nothing more than a spacer, or guard, to protect the tuning gear drive from getting knocked out of alignment when the coil assembly is removed from its wooden case. I say ‘longshot’ because a 2-inch piece of 3/4-inch wooden dowel would have been a far cheaper and simpler solution for this type of problem.

Adding to this mystery is the complete lack of reference anywhere in the 52-Set documentation to these resin cylinders.



David