Wireless Set No. 52 Canadian - Project

[David Dunlop]

Well it took a while, but my spare parts receiver has now finally been carefully reduced to its basic chassis assembly. It has been an interesting and informative bit of work. I now have a far greater appreciation of the incredible amount of design and planning work that goes into producing a piece of equipment like this in the pre-computer era. I started out just thinking of the line workers actually assembling it, but it is so much more than that, involving a lot more people with a huge variety of other skills.

The process also gave me a much better understanding of the layout of all the components and their interactions with one another in the various circuits in the receiver. Useful things to learn in this project!

The basic foundation of this receiver chassis turns out to be just four pieces of 13-guage, steel, sheet metal.

The main piece of sheet steel runs from the ½-inch lip at the upper rear, across the top, down the back and forward across the bottom, where it then drops to form the lower front section of the chassis and ends with another ½-inch lip folded under the front lower edge. Half-inch tabs are also present on this piece, folded back along the sides where they meet up with the two side panels. These side tabs provide a means for the spot welding to take place joining the three main chassis pieces together. The overall size of this piece would be on the order of 25-1/8 inches long and 15-7/8 inches wide. Where any tabs are located at folds, they were designed that outside corners would be full open at 90 degrees and any inside folds were set up for a 45-degree mitre.

The two side panels are basic dimensional mirror images of each other, 11-1/4 inches wide and 14-7/16 inches long, with ½-inch tabs, front back and bottom only. They really differ only in the hole patterns punched in each.

When the cutting, punching and brake work was completed on these three pieces, they were inspected and a small circular CMC Inspection Stamp was punched into them, ready to move down the line. The first two photos attached highlight these features.

The fourth piece of sheet metal making up the receiver chassis is a strip approximately 1-1/8 inches wide, folded in half lengthwise down the middle forming two ½-inch tabs at 90 degrees. This piece is 13-3/4 inches long with straight cut ends, and forms the lower rear edge of the chassis. It is butt welded in place with all external seams filled and ground smooth.

The spot-welds on the tabs connecting the main and side chassis panels are approximately 1 inch apart wherever possible and ¼-inch in diameter. The second photo also shows how the lower chassis strip and the upper rear edge both have all their external seams filled and ground smooth.

Photo 3 shows the inside of the lower chassis strip with the unfinished butt welds. Note that the zinc plating covers these welds. By ensuring all these external seams are smooth, it makes sliding the receiver in and out of its relevant Carrier that much easier for the Operator.

A number of smaller sheet metal pieces are spot welded to the chassis prior to it being zinc plated, but I am not sure if these small pieces would have been added to the individual chassis panels before they were assembled into one unit, or after.

The first two are the Upper Mounting Brackets passing through slots on either upper front side. These are made of heavier, 11-guage sheet metal. They have an offset stamped into them such that when the rear portions of them are spot welded to the chassis sides, the outside faces of the front sections projecting through the slots, line up perfectly with the outside face of the chassis side panels. This ensures a good fit when the receiver chassis goes in and out of its Carrier. The last photo in this Post shows this offset on the Upper Left Side Mounting Bracket.

The fourth Photo here gives a rear view of what is going on around the Right Side Mounting Bracket. Two other 13-guage metal strips are also fitted here.

The long vertical strip is a stiffener to support the Upper Front Right Subpanel Assembly. This is the small panel that sits directly behind the removable Upper Front Panel of the receiver, which supports the BAND Switch, FREQ ADJ Switch and AERIAL Terminals visible outside the receiver, as well as the Gas Discharge Tube Clips mounted inside, behind the two Aerial Terminals.

The larger, horizontal strip of 13-guage steel mounts the AirLoc Fastener Receptacle. A blue, spring steel spring assembly is held inside this receptacle. Note that the entire thing is covered in zinc plating.

The rest of the chassis information will follow shortly.



David

[David Dunlop]

Continuing on with what I have found when disassembling my spare parts receiver, the 1st Photo in this Post shows a front view of the three machine screws used for mounting the right rear side of the Coil Assembly RF to the back of the Receiver Chassis. They are slotted, pan head machine screws, 7/16-inch long by 6-32 NC in design.

A rear view of these three screws is in the 2nd Photo. Once they were screwed in place, the heads were welded to the chassis and then ground down to avoid any contact with the leads from components mounted on the PANELS, Phenolic, 22-Tag ZA/CAN 4690 (Discussed in Post #616.) that gets installed directly behind these screws later in the assembly process. Note the welded heads have been zinc plated.

The three small Grid Cap Clip lead holes with the metal sleeves pressed in place, and the larger sleeve for the AGF, NOISE LIMIT and HET TONE Switches sub harness are also all zinc plated, so must have been fitted before the plating process as well, along with the 15 small hollow threaded spacers riveted on the chassis for mounting the Tag Panels. The crimps on all these rivets show no plain steel at all, just zinc plating.

The one remaining item that was riveted to the chassis is the 2-3/4 inch solid steel support for the lower inside corner of the 8-Pin Connector Mounting Plate. The third photo in this post shows this support in place, and the fourth photo shows the back end of this support rivet head. All of it again, zinc plated. The open end of this support is tapped 7/16 inch deep for one of the 8-Pin Mounting Plate Countersunk screws.

The last Photo here today shows the 13-Guage reinforcing strip spot-welded under the upper right rear lip of the main chassis plate for the upper two mounting screws of the 8-Pin Connector Plate. If you look closely in the 4th Photo, you can see that the metal from the main chassis panel has been cut back with a countersink just to the point of the reinforcing plate beneath it. I believe this was done to avoid the two mounting screws from grabbing both pieces of metal when threaded home and spreading the two pieces apart in the process. The kind of thing that can happen, when you try and screw two pieces of metal, or wood together sometimes.

Once all these pieces were assembled. The chassis would have been zinc plated and inspected. All three main chassis parts show circular, blue, C.M.C. Inspection stamps on them. The chassis then probably received its Production/Control Number, and then had the blue Component Location ID marked applied and spot varnished. The next logical step would be installing all the Valve Holder Assemblies, and then, perhaps the Main Wiring Harness.

As I noted in the previous Post, this disassembly has been very interesting, though time consuming to do. And I needed the diversion to clear my head a little. I now plan to get back to getting the Main Set Receiver back up and running properly.


David

[David Dunlop]

True to form in a project of this size, I was cleaning up the shop a bit this evening and ran across a ziplock bag containing a single Capacitor and Cleat Assembly I had not yet catalogued.

While looking the capacitor up in the Master Parts List, I ended up flipping past the page with the CAPS, Holders, Watch, No. C1 on it. Something I have done countless times before. This time, however, something in the shading of the illustration of this part, along the front face, caught my eye. It appeared to be a rendering of the ZA/CAN Number cast in raised letter in the Bakelite. That jogged my memory.

About two years ago, I ran across an ad on-line from a chap in England who was selling NOS Bakelite Pocket Watch Holders. If I recall correctly, they were originally packed 10 to a box and he had several boxes of them available for sale. Since both my 52-Set Receivers were missing their Pocket Watch Holders, I ordered a pair.

When they arrived, I had noticed they had the ZA/CAN Number cast into the front face of the Caps. Checking the two Pocket Watch Holders on my Mk II and Mk III 19-Sets, I found both Caps were smooth, No sign of a number of any kind on them at all. At the time I just assumed the ones I had just ordered were probably British made NOS and thought nothing more of it.

Now I find the cast ZA/CAN Number on those two Pocket Watch Holders is what shows up in the 52-Set Master Parts List. Late discovery, but nice none the less.


David

[David Dunlop]

Well it was an interesting weekend, lots of pluses for the most part, and fortunately, only one rather spectacular negative.

I was able to narrow down the possibilities for the poor performance of my Main Set Receiver to the 1st and 2nd IF Amp sections and Valve V1D in particular. The valve itself was in good working order, but one of the other components that should have been working well with it, was not.

So I took the receiver, along with my Remote Supply bits over to a friends on Sunday morning to take advantage of his far greater electronic expertise, and shop full of test equipment.

As I had suspected, the receiver was working very well both ahead of and behind the two IF Amp stages and we eventually worked our way towards the eight small trimmer capacitors set up in two banks of four in the pair of IF Coil Assemblies. This receiver, as in my Remote Receiver, has the upgraded Trimmer Capacitors that were issued 24 April 1959 for replacement of the originals.

These new capacitors were identified as:

CAPACITORS, Variable, air dielectric 7.5 to 99.0 uuf CT1B100 and came with a NATO Stock Number 5910-00-126-1583

I suspect they are a Hammarlund product and the ‘CT1B100’ might be their part number reference.

The original capacitors issued with the 52-Set were also very likely made by Hammarlund. They are described as:

CAPACITORS, Semi Fixed, 5 – 100 uuf, 10% ZA/CAN 4478

The first we attempted aligning, C7D, would not budge at all and we could see it had a coat of varnish on it, none of the other seven had showing. That should have been our first clue. Five of the remaining seven were almost spot on and needed little or no adjustment. The two others were off by quite a bit and things were sounding very promising as they were brought into alignment. That just left C7D, so we headed back to it.

With the second careful attempt at turning the inner adjusting shaft, it suddenly unfroze and started turning and things were sounding REALLY good! It was just coming up to its optimum alignment point when we heard a loud metallic ‘ping’ from inside the capacitor, the adjusting shaft parted company with the adjustment tool and bottomed out deep inside the outer support tube, and the small hex head collar that locks the shaft in position bounced onto the bench. Not good!

An inspection of the hex collar showed it was cracked right through one face and the crack had a lot of dirt in it, all the way through. Taking into consideration the air gaps between the fixed stator and adjustable rotator plates inside this capacitor are on the order of 1/64-inch wide, and the adjustable rotator shaft suddenly moved inward under its tension spring load a good 5/16-inch. I am pretty much assured this capacitor is now toast.

The two photos show the shaft settled deep inside the capacitor now and the crack through the hex collar.

I do have 8 of the original capacitors available from the Spare Parts Receiver and a quick look indicates they are probably all in good working order, but it would be nice to find an original upgrade version for the replacement project.

OF course Hammarlund went out of business in the late 1970’s, so another challenge ahead with the Main Set Receiver. Sigh!


David

[David Dunlop]

A little bit of an update on the C7D Trimmer Capacitor Saga.

I have been able to successfully retrieve the C7D Trimmer Cap from the spare IF Coil Assembly salvaged from my Spare Parts Receiver. Only two soldered connections to deal with, both involving a very tight wrap of 20 gauge solid copper lead, and I have never seen so much solder on connections like these two had accumulated. I used up nearly 3 inches of de-soldering wick on them before deciding there was no way I was going to be able to clean the terminals enough to unwrap the leads. So I had to finally resort to my least used and least favourite tool in the shop: cutters.

But the replacement C7D Trimmer Cap is now ready to install in the Main Set Receiver, along with its insulating shield for the long Rotator Plate Connector.


David

[David Dunlop]

The Project is in a temporary holding pattern for a while.

I realized once I had the spare C7D Trimmer Capacitor ready for installation, I did not have any 20 gauge tinned, solid copper hook-up wire available in black insulation to make up the two connections between the C7D and its related coil. I have now ordered a 25-foot spool from the local Electronics Shop and have to wait for it to come in for pickup.

In the meantime, I have continued to review the steps needed to do the swap of the Trimmer Capacitor in the Main Set Receiver. It has been an interesting process with several modifications taking place in my head over the last few weeks.

Step 1 is I have to unsolder the Grid Cap Clip for Valve V1D inside the front section of the receiver and solder on a temporary extension of about 6 inches. This lead only has 2-3/4 inches of free place with the Grid Cap Clip removed before the lead will disappear inside the coil shield. The shield cannot be removed because there is not enough clearance to do so with the front panel attached to the receiver. The extension will allow me to retrieve the Grid Cap lead and re-solder the clip to it when the swap of C7D is completed.

Step 2: On the back side of the receiver, as shown in the attached photo, The C7D Trimmer Cap is the top most component on the left hand diagonal IF Coil Assembly. From approximately the mid-point of the assembly to the top, there are three individual wires that will have to be unsoldered: a long one going up above the coil assembly and a medium and short length set at roughly the mid-point. With them free, the large wiring loom coming off the bottom of the coil assembly, leading to the SHARP/FLAT Switch is the only thing holding the coil assembly in place once its mounting screws are removed.

The two IF Coils are 3-3/4 inches long wrapped on brown phenolic tubes. Strips of cotton cloth tape hold them in place on the tubes and then the entire coils are dipped in bees wax to protect the very fine wiring of the coils.

The punched holes in the rear chassis panel have some pretty keen edges. It would not take much contact with them for the wax and wire coils to be trashed, so the entire assembly has to come straight back out of the holes roughly 4 inches to be safe.

The loom feeding to the SHARP/FLAT Switch has been sitting in that position for nearly 70 years and I have no way of telling for certain if it is natural or synthetic rubber. The wires have also been treated with fungicide varnish so overall are pretty stiff. There is only about 2-1/2 inches of play in that loom before it reaches its limit and the coil assembly will start to get pulled to that side. Not good.

My first thought was I would have to unsolder all the connections at the SHARP/FLAT Switch, which was not a popular thought in my head. I then remembered the disassembly process for the Spare Parts Receiver.

The only electrical connections at the back of this switch are to the two IF Coil Assemblies. The switch has a big long shaft that runs to the lower front of the receiver and the hole in the front of the chassis simply supports the shaft. The switch is actually held in place on the chassis by a mounting plate at the back end with two screws securing it. For reference, there is a photo of this switch in Post #633.

Step 3, therefore, will be to remove the knob from the front of the SHARP/FLAT Switch shaft and then remove its two mounting screws. The entire switch can then be moved back to clear the front panel of the receiver and then swung down and to the right in the attached photo to rest directly under the two IF Coil assemblies. It can then be careful moved straight back with the IF Coil assembly containing the C7D Trimmer Cap until the two coils clear the rear chassis panel. With lots of TLC…it should work…I hope.


David

[Bruce Parker (RIP)]

Originally Posted by David Dunlop

I have now ordered a 25-foot spool from the local Electronics Shop and have to wait for it to come in for pickup.

25 feet should cover this and many subsequent 52 set rebuilds. Are you not telling us something?????

Anyway great restoration and it's always a pleasure to see how you come up with modern solutions to 75 year old problems. I bet you are the only one of 7.9 billion people doing what you're doing.

And besides all of that, 52 sets are some perdy.....