Wireless Set No. 52 Canadian - Project

[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

[Mike K]

Originally Posted by David Dunlop

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.


David

Yes I believe they are just spacers that provide some mechanical stability to the rotary inductor frame and also prevent damage to the inductor unit mount which looks like a phenolic sheet material.

[David Dunlop]

Hello Mike.

The frame work is actually 1/4-inch phenolic plates, assembled at the factory with zinc, or cadmium plated, brass brackets and hardware, another part of the design showing CMCs desire to avoid the presence of ferrous metal in the construction of these Coils, Aerial Tuning No. 2 A, at great length.

They seem to have not wanted any latent magnetism developing within these units at all costs, and I fear I am not yet wise enough to understand why. Insert “Sigh” here.


David

[David Dunlop]

I have pulled this photo up again because it shows really well the four sets of components that are fitted to the wooden case for the coil, once the coil assembly itself has been removed. In order to refinish the wooden case, all four of these sets need to be removed. These components are as follows:

1) Aerial Output Terminal - located on the upper left rear side panel. The tip of the socket assembly for it is just visible in the upper left corner of the photo.

2) Input Terminals - there are two of these fitted with wing nuts located one on each lower rear side panel. The inner brown phenolic mounting strips are clearly visible inside the back of the case.

3) Panel Mounting Brackets - three each across the upper and lower front of the case.

4) Case Mounting Plates - mounted to the bottom of the case, one each side.

It should be noted, that with the exception of the casual mention of the two above terminals in the Operators Manual, none of these IDs are official and none of these parts can be found in either Issue 1 or Issue 2 of the Parts Lists for the 52-Set. Some of the individual parts making up these items are listed, however, but not all. I guess I should also point out here that I recently ran across a few pages from an Issue 3 of the Parts lists, dated 2 January 1953. I have no idea at this point if this was a few random page updates, or another full revision.

I shall cover the removal and descriptions of these four components in the next four posts.



David

[David Dunlop]

The first component I decided to remove from the coil case once the coil assembly had been removed was the Aerial Terminal. Not because it is in the way of anything else to be removed, but for the simple reason it is the most fragile component, which sticks out too much. The two main pieces of it are also in the realm of Unobtanium should they be broken.

This item is not referenced at all in the Parts lists as a complete assembly at all, but three components of it are, as follows:

1) INSULATORS, Ceramic, Bushing, Female ZA/CAN 4596

2) INSULATORS, Ceramic, Bushing, Male ZA/CAN 4661

3) SOCKETS, Antenna, w/sleeve, No. C1 ZA/CAN 4593

The last component is cadmium plated, 1/2-inch brass hex rod, fitted on its outer end with the cadmium plated brass socket with sleeve. The inner facing end is fitted with a 10-32 x 2.75-inch cadmium plated brass rod.

A pair of .020 inch thick brown phenolic gaskets fit between the insulators and the wooden case, one each side. These were custom made for the application. I found both of these gaskets had become glued to the NATO Green paint since 1966 which was a little concerning. I found bt using a 4-inch steel putty knife at very shallow angle, the paint was thick enough I could slowly press into it to get the blade below the gasket and slowly lift it. As the gasket slowly came up, I gradually advanced the blade until the entire gasket popped free. This worked for both the inside and outside gaskets.

These three pieces are clamped to the left side of the wooden coil case with a 1/2-inch OD 10-32 plated brass flat washer, plated brass 10-32 Shakeproof washer (internal tooth lock washer) and a plated brass 10-32 hex nut. When the connection is made to the internal feed from the tuning coil assembly, a 7/16-inch OD 10-32 plated brass flat washer is slide down against the hex nut already in place, the feeder cable fitted and then a second 10-32 Shakeproof washer and hex nut added to secure the connection. I am missing the second Shakeproof washer but have a few extras in my parts supply for when reassembly takes place.


David