Wireless Set No. 52 Canadian - Project

[David Dunlop]

Continuing with the COUNTERS and their Coupling arrangements, lets take a look at how the Canadian Marconi Company dealt with this issue on the two PA TUNE Coils in the 52-Set Sender.

At the moment, the two in my Sender are still in situ and next to impossible to get at, so I will resort to using the illustrations of the relevant parts out of the Master Parts List.

The first photo is the Coupling Arm that is fitted to the COUNTERS side of the drive system. It is a tapered metal channel with a large post fitted to the wide end which serves as the mounting collar. Roughly midway down the channel an small capped pin is fitted and at the narrow end, a small slot is centered parallel to the longitudinal axis of the channel.

The second photo is of the Coupling Arms that fits on the Coil side of the PA TUNE drive assembly. This one is a rectangular, brown, phenolic plate with a small bushing post at one end and a small pin at the other. This pin has a small hole through it at the top end.

The third photo is the Coupling Spring, which when installed, provides tension to the entire Coupling Drive Assembly to remove any play in the system. In this configuration, the COUNTERS would be set to “))))” and the Tuning Wheel on the relevant coil brought all the way forward to its start point. The two Arms would be parallel and one over the other, such that the pin in the end of the Phenolic Coil Arm, passes through the slot in the steel COUNTERS Arm. When all was in place, the straight end of the Springs would be inserted in the small pin and the angle midway down the springs placed around the capped pin on the COUNTERS Arms. The curved end of the Springs is then brought across the COUNTERS Arms to wrap around the base of the large bushing. The end result is shown in the last photo.

This design also produced a drive mechanism with no slop in it at all and an instant response from the COUNTERS Dial as the PA TUNE knob is turned and the Wheel on the coil starts to move. What I don’t understand at the moment is why Marconi used two entirely different designs for basically the same purpose.


David

[David Dunlop]

The last oddity/difference in COUNTERS installation between the COIL, Aerial Tuning and the Sender has to do with the little six-sided metal plate and Locking Nut Posts fitted to each item.

The first photo shows these two items on the front panel of the Coil, Aerial Tuning. The plate measures 0.067 inches thick and the base of the Locking Nut Post 0.055 inches thick.

The second photo is of the same two items found on the front panel of the Sender. Here, the plate measures 0.125 inches thick and the base of the Locking Pin Post 0.125 as well. The second mystery. Why wouldn’t Marconi have used the same sized plates and pins for both pieces of equipment?


David

[David Dunlop]

One last little bit on these COUNTERS on my 52-Set Sender. As per the first photo attached, the PA TUNE COUNTERS on the left side had been overextended at some point and no longer reads “0000” when it should.

After a careful study of the COUNTERS on the front panel of my parted out COIL, Aerial Tuning, I was able to confirm the removal of the three large screws (one upper in the decal and the two lower ones in the tack welded plate added around the dial shaft assembly) will free the complete COUNTERS assembly from the front panel, as shown in the second photo. This will hold true with the front panel of the Sender as well.

At that point, I should be able to loosen the four small screws around the actual indicator dial just enough to allow the gears to be freed from one another. See the last photo. I should then be able to re-zero the COUNTERS and retighten the four screws carefully to bring the two gears back together and problem solved on that front.


David

[David Dunlop]

One other oddity I forgot to mention with these Counters.

If you take a close look at the two sets of photos in Posts 280 and 281, you will notice the gears and drive bushings are all fitted to their respective shafts by taper pins on the Counters used with the Coil, Aerial Tuning No. 2A

On the Counters used in the Sender, these gears and bushings are all mounted by means of Bristo Set Screws, which have been doubled up on each gear, each pair set 90 degrees apart.

David

[David Dunlop]

The next stage of the Sender front panel disassembly has been working on the removal of the Blower assembly from the access door. The first step in this is to remove the COVERS, Metal, Blowers, Electric from the front of the door. This is necessary to gain access to the three machine screw heads of the hardware holding the mount for the blower motor in place.

I found the ¼-Drive Socket Set worked best for this when a universal joint was added between the socket and handle as the upper two nuts holding the COVERS in place are quite close to two of the motor mounts on the inside of the door. Clear lacquer has been used to secure the nuts, but they break free quite easily.

Interesting to find the screen on the front of the cover had a small trim strip of metal folded over its edge. It keeps all the sharp ends of the screen wires out of the way, likely prevents the screen from unravelling and provides a good mounting surface for the 12 spot welds used to secure the screen behind the front lip of the COVERS.

The four posts used to mount the COVERS to the access door are described as:

SCREWS, Spade, 6-32 x 11/16-inch No. C1 with a 0.144-inch dia. hole in the flat end. ZA/CAN 4372

This hole takes a small rivet used to mount the screw to the inside of the rim of the COVERS. The four screws are fitted in a square pattern around the COVERS rim.

Once the COVERS has been removed, one can clearly see the three slotted, round head machine screws holding the Blower Mount in place. The crud on the fan blades is largely just dust with some zinc or cadmium oxide build-up, but it all rubs off rather easily.


David

[David Dunlop]

Removal of this assembly from the Access Door is going to be nice and simple by looks of it.

Only one wire needs to be disconnected, which is the main feed line from the 8-Pin Plug on the back of the Sender running up to feed into the RF Choke L30B (tied in place on top of the board), and the Capacitor C3AF, mounted directly underneath the choke on the bottom of the board.

The entire motor assembly at that point can simply be removed as a unit by removing the three Machine Screws.

David

[David Dunlop]

I was sitting staring at the Sender this morning with a fresh mug of tea, when I noticed a detail about these PLATES I had missed in my earlier Post #274 regarding them. Not that what I noticed provided any answers to the mystery already identified. It just adds to it.

As you will notice in the first photo attached, all five of the PLATES, Stop, No. 1 fitted to the Sender panel are dimensionally identical to each other. Some look a bit wider but that is just dirt accumulation on, and around them. What I did not notice earlier, however, was that the spacing, centre-to-centre for the rivet and set screw on the lone PLATES for the PA TUNE Dial, is a lot shorter than the other four plates to its left.

The PA TUNE PLATES has a centre-to-centre mounting space for its rivet and set screw of 9/16 inch. The other four are all 1 inch centre to centre for the same measurement.

I checked the measurement on the two PLATES on the 52-Set Receiver and, as shown in Photo 2, they are both showing the wider (1 inch) centre-to-centre distance.

Now my curiosity is really peaked! Not only do I not understand why only one PLATES was used for the PA TUNE Dial, with installation for a second PLATES partially abandoned, but now I would love to understand why a different hardware mounting pattern was used for the one lone PA TUNE PLATES.

This is probably boring as hell detail for most of you, but with so little documentation about the design and production of the 52-Set having survived from the Canadian Marconi Company, I thought noting these detail bits here at least preserves the information, and if none of us can figure it all out now, perhaps somebody down the road will.

David