Wireless Set No. 52 Canadian - Project

[David Dunlop]

This pair of shields cover the upper pair of coils (from left to right L19A and L17A) in the Coil Assemblies, IF, and differ from their lower counterparts only by the presence of small, metal sleeved holes in the end of them to allow the Grid Cap Clip leads from the coils inside to pass through.

Just enough of a difference to get an ‘A’ added to the end of their ID and a new ZA/CAN Number.

With regards to removing these shields, you have no choice; the Grid Cap Clips must be unsoldered from the ends of the leads. These leads are not long enough to allow the shields to slide up far enough on them to access their solder terminals inside the Coil Assemblies.

Once the Grid Cap Clips are removed and the mounting hardware removed behind the chassis wall, the shields lift off easily.


David

[David Dunlop]

Viewed from the front of the receiver, this is the left hand vertical pair of IF Coils, under Valve V1E, the 2nd IF Amplifier. The upper coil, L19A deals with the input to the 2nd IF Amplifier Valve V1E, and is supported by a pair of Variable Capacitors, C7G and C7H, acting as Trimmers. The Grid Cap Clip lead for V1E feeds out of the shield for L19A.

The lower coil, L18A, deals with the output from the 1st IF Amplifier Valve, V1D and is supported by a pair of Variable Capacitors, C7E and C7F, acting as Trimmers.

In the early production receivers, these trimmer capacitors were quickly identified as prone to failure in humid conditions and were replaced with much better ones and instructions were issued to upgrade the earlier capacitors when found in a set.

For the Grid Cap Clip lead in this Coil Assemblies, a lead wire would have to have been fitted, of sufficient length to exceed what was needed. The lead would have been fed through the shield and soldered in place, once the coil assembly was mounted in the receiver chassis, and a sleeve fitted over the soldered terminal. With the shield then mounted over the coil, the lead could then be trimmed to the required length, a black sleeve slipped over it and the Grid Cap Clip soldered in place. The sleeve was then tied in place. The sleeve on this Clip was a black woven one.

On the back of the chassis wall, six sets of slotted, round head SEMS screws and external toothed lock washers mount the entire coil assembly to the chassis. When the screws are removed, and the two shields up front, the entire assembly can be carefully pulled out of the back of the chassis. Use caution, however, as the black sleeves on the lower soldered terminals of the assembly make the fit quite snug. It does not hurt to compress these two sleeves inward slightly with one hand while extracting the assembly with the other hand, until the sleeves are clear of the rear receiver chassis wall.


David

[David Dunlop]

Virtually all the parts of this Coil Assemblies are identical to the one just discussed in Post #642, but because the electronic parts have different circuit reference numbers for maintenance purposes, this assembly gets a different Identification Name and CMC Part Number.

This assembly is located under Valve V1D when viewed from the front of the receiver chassis.

The upper Coil L17A, with the Grid Cap lead, deals with the input to the 1st IF Amplifier Valve V1D, and the lower Coil deals with the output of the Mixer Valve V1C.

Two Variable Capacitors, C7A and C7B act as trimmers for L16A, and two other Variable Capacitors, C7C and C7D act as trimmers for L17A.


David

[David Dunlop]

This Unit sits on the left side of the rear wall of the receiver chassis, directly under Valve V2A. The Circuit Reference is L20A, in the 2nd IF Amplifier circuit for Valve V1E. It acts as the coupling from V1E to V2A.


David

[David Dunlop]

This Unit, circuit reference L21A, sits under Valve V1F on the far left side of the rear chassis wall of the receiver. It is externally identical to L20A, except the coil within it has a larger OD than the coil in L20A.

Unit L21A forms part of the Het Oscillator circuit of Valve V1F.


David

[David Dunlop]

A bit of a collective title to cover off several related receiver parts all at once.

The 52-Set Receiver uses two British Valve types (Canadian Equivalents) for the main operating chassis, factoring out the self-contained Crystal Calibrator sub-assembly. There are eight ARP-3’s and a pair of 12Y4A’s. Both of the sockets for these valves are of a brown, phenolic board design, rather than Bakelite, or ceramic.

HOLDERS, Valve, 5-Pin, on 1-27/32 inch centre mounting holes, ZA/CAN 4734, are used for the 12Y4A’s.

HOLDERS, Valve, 7-Pin, on 1-7/8 inch centre mounting holes, No. C1 ZA/CAN 4305, are used with the ARP-3’s.

Both of these Holders mount from the bottom, or back of the chassis, using a pair of truss head, 1/8-inch diameter by 5/16-inch long, soft steel, tubular rivets. Commercially today, these two valve sockets/holders are known as ‘5-Pin’ and ‘B&’ sockets respectively.

At the same time as the above two Holders get installed on the receiver chassis, a third part is also fitted to the top side, or front, of the chassis to be secured by the same two rivets coming up from behind the Holders. This part is as follows:

BASES, Metal, Shields Valve ZA/CAN 4524.

In the three photos attached, the 5-Pin Holders are on the left and the 7-Pin on the right, with the Bases below them with the rivets.

Removing these Holders and Bases was relatively straightforward. I used a large enough drill bit in my cordless drill to cover the circular crimped rim of the tubular rivet in the base mounting holes. With the crimp shaved down about half or so, I then took a 4-inch Common Nail, centred it on the hollow end of the rivet and gave it a whack with a hammer. The point on the 4-inch nail was just long enough to push the rivet out the chassis metal with no damage to the Base.

There was an interesting discovery about these two Holders as the rivets came out.

Both Holders are made up of a sandwich of two phenolic plates. The Pin Terminals are crimped onto the lower plate. The top plate is then added and riveted in place by hollow brass rivets.

On the 5-Pin Holders you can see a pair of these small rivets at the 10 and 4 o’clock positions near the rim of the Holders. The Pin Terminals on these 5-Pin Holders are thin enough metal they lay quite flat against the top face of the lower phenolic plate when fitted in place. The top phenolic plate helps hold the Pin Terminals in place and also likely stiffens the overall Holder. When you look at the edge shot of the Holders you will see very little gapping between the two phenolic plates. Not so with the 7-Pin Holders.

The Pin Terminals for the 7-Pin Holders are quite robust by comparison to the ones on the 5-Pin Holder and they do not lay flat against the top of the lower phenolic plate at all. A large tubular brass rivet is used at the centre of the 7-Pin Holders to secure the top phenolic plate in place. This leaves a noticeable gap between the two plates, which if not resolved, would likely warp the Holders when riveted to the chassis causing long term problems.

To solve this problem, small phenolic washer-like spacers were inserted between the two phenolic plates to take up the gap where the mounting rivets were placed. During the manufacture of these Holders, these spacers were very likely lacquered in place to secure them, but after 80 years, the adhesive quality of the lacquer has failed completely. As I happily popped the first set of these holders off the receiver chassis, I was surprised to find several of these spacers on the workbench, along with a lot of fine yellow dust. Fortunately, all spacers were accounted for in the end.

The assembly station on the line where these Holders were fitted is another one I would like to have seen in action.


David

[David Dunlop]

Another generalized title to cover off the following three, related components in the Wireless Set No. 52 Receiver.

BODIES, Shields Valve, 1-5/8 inch dia. x 2-7/8 inches long, No. C1 ZA/CAN 4279

This item is made of nickel-plated tin, the upper end of which has been rolled back in on itself forming an inner open ring. Inside this ring, a felt washer has been cemented in place. This washer has a ¼-inch square cross section, a 1-inch ID and a 1-3/4 inch OD. This felt ring rests on the shoulder of the valve and when the Shield Body is fully seated in its BASE, the Valve will be fully seated in its Holder.

As per the example of this Shield Body in the first photo, the nickel plating can often wear off the tin externally. Not sure why, but the insides and the upper and lower ends of the outer surfaces that are covered by the Base and Cover, stay in pretty good shape. I have considered redoing the nickel-plating on these Shield Bodies but that would mean soaking the inner felt washers in a solution loaded with nickel ions that would stay in the felt once dried out and I am not sure that would be a good thing for the proper operation of any valve in the future.

COVERS, Metal, Shields Valve, 1-11/16 inch dia. x 1-3/4 inches long ZA/CAN 4233

These are the commonest Covers found in the 52-Set Receiver, with a single side slot for accommodation of a Grid Cap Clip lead if needed. They are made of a slightly heavier gauge of zinc-plated steel, for some reason. An example is in the second photo.

BODIES, Shields Valve, 1-5/8 inch dia. x 2-5/32-inches long, No. C1 ZA/CAN 4280.

This Shield Body was designed solely for use with the 12Y4G Valve used in the V2B, Noise Limiter in the receiver. This is a horizontally mounted valve found on the lower left corner of the rear chassis panel, directly behind the vertically mounted V1G Valve. Since clearance needed to be provided for the Wireless Operator to reach in and service/replace the V1G Valve, sufficient space was needed behind the V1G Valve to do so. Consequently, the standard Shield Body was shortened in length. This meant there was no easy means for the full shielding assembly of this horizontally positioned valve to be physically locked in place and there was the risk of the Shield Body vibration loose. Consequently, the solution Canadian Marconi came up with was to solder the Shield Body into its Base. In the third photo you can see the red lacquer markings from the factory on this solder work. The V2B Valve is an annoying valve to have to work on in this receiver. Tricky to remove from the shield and even harder to line up blind with the Holder to put it back in place.


David