Wireless Set No. 52 Canadian - Project

[David Dunlop]

A small bit of work done on the Sender this passed weekend, but highly productive.

I was able to successfully remove the two tubular rivets securing what was left of the TERMINALS, Aerial, No. C1 mounting plate to the Sender front panel. If you refer back to Post # 302, you will see the three mount fragments and the back end of the two rivets. The second photo in Post # 308 shows the two truss heads of the rivets from the front of the panel.

I lined the table of the drill press with an old face cloth to protect the front panel paint and went with a 3/16-inch drill bit to cut back the cinch ring on the back of the rivet, being sure to stop the cutting before the centre of the bit got too close the brown phenolic mounting plate.

It was important to be able to identify these rivets to source proper replacements, so once the ends were cut back sufficiently, I switched to a 7/64-inch drill bit to use on the drill press as a punch pin to try and press the rivets out of the front panel. I was a bit wary of this, as generally speaking, drill press spindles are not built to handle that kind of excessive load, unlike a milling machine spindle. But with some gentle increase in pressure, out they both popped.

Before I had started this work, I had assumed these two rivets were plated brass. As the drilling phase progressed, however, the shavings kept coming up bright, shiny, silver. Once the rivets were free, a quick check with a magnet showed they were actually steel. That was a bit of a surprise as I was expecting aluminum.

In any event, they spec’d out to be truss head tubular rivets, with a 7/32 –inch diameter head. Shank diameter is 1/8-inch. Original length was no less than 3/16 –inch and no longer than 7/32-inch. From what I have read on this style of rivets, length is critical to get the job done without damaging parts being held together.

I am going to go with aluminum replacements, as they are the easiest to work with. Particularly when holding thin brown, phenolic board without crushing it to pieces and I only have one replacement available to work with. As it turns out, I can source sizes at both ends of the possible range I came up with exactly, as well as a 7/32-inch length in the middle of the range. I will order in a selection of each.

Now I just have to find an inexpensive hand tool for setting these rivets. The most promising I have seen so far is a C-Clamp style to tool with several interchangeable heads. I will likely only ever use it a half dozen times or so, so don’t need to break the bank There are some countersunk head tubular rivets I need to replace in this 52-Set Project as well, so I need to look into those next.

David

[David Dunlop]

I found one of these a little while back and it arrived in this afternoon's Mail. a lot more compact in real life than I had imagined for some reason. Would have been nice if the Aerial itself had survived, but I think it might be a relatively easy item to replicate down the road.

Now I just need to find the matching Reels, Cable No. 2 Mk II to go with it.

David

[David Dunlop]

I have been side tracked for the last couple of weeks with the discovery and purchase of a minty Tektronix Type 500A Oscilloscope Cart for the Type 545A Oscilloscope I restored earlier this year. Quite nice to be able to glide the 65 pound scope about the shop now and not have to carry it anymore.

With that out of the way, I was able to return to sorting out the shattered AE Terminal Board on the Sender front panel. Once I had drilled out the two rivets holding the remains of the original board to the front panel, I was able to measure the PCB board bits and found them to be 1/16 inch thick and was able to get an old terminal strip of this thickness from a friend in town.

With the terminals all drilled out of the donor board, I was able to scribe out the dimensions of a replacement for the Sender AE Terminal: ¾ “ x 1-1/4 inch. A 5/32-inch hole was then marked out at the centre of that board, and on either side of that hole, a 1/8-inch diameter hole, balanced on 7/8 inch centre to centre.

I drilled the holes out first while the larger sheet of PCB was easier to work with, and then used a 40 tooth per inch X-Acto back saw I bought years ago for a 1/6 Scale Tiger Tank RC Model project, to trim out the required board. Smoothed up the edges and holes with a set of X-Acto Needle Files purchased for the same RC project and another restoration task ticked off the list.

David

[David Dunlop]

Thought I had better document this little bit of information before moving on, as it relates to the countersunk rivets used in the 52-Set, which are not catalogued in the Parts Listings.

I had initially hoped to be able to salvage the AE Terminal Board from the front of the parts receiver I have available and cut it down to make the replacement for the broken board on the Sender front panel. I knew the AE Terminal Board on the receiver was fastened with countersunk rivets, which I was going to need specs for in any event, as the same rivets were used to mount the Airloc Cowl Fastener Receptacles on the receiver, and the right side one on my Main Set Receiver was broken.

Removing the panel holding the Receiver AE Terminal Board was easy enough, as was drilling out the four rivets holding the board to the panel. It was at this point, however, I confirmed the board would not work at all on the Sender front panel, even if a correctly sized piece could be cut from it. The rivet spacing on the receiver board was on 1-inch centres. The Sender board needed only 7/8-inch centres. Also, the board on the receiver is subject to a lot more stress and strain than the Sender board. The receiver board holds a Gas Discharge Tube clip on the upper terminal and the large conventional aerial socket on the lower terminal that requires a lot of direct in and out push/pull force. Hence, a 3/16 inch thick board was used here, rather than the 1/16 inch thick board on the Sender.

The good news out of all this, however, was that the four countersunk rivets were retrieved and spec’d out.

These turned out to also be mild steel with a 1/8-inch diameter shank. The countersink is 90 degrees, and the head diameter of the rivet at the flat is 0.220 inches. The length for these would have been ¼-inch, but other lengths were used due to differing thicknesses of material things were fastened to on the set.

David

[David Dunlop]

A bit of a milestone has now been reached with the work on the 52-Set Sender. I have done all the cleaning I can now with the chassis resting on its back. One small section of the lowermost chassis stills needs to be cleaned – the area surrounding the socket for the 813 valve – but I cannot easily access it until the chassis is returned to its upright position. This, however, cannot be done with all the components normally secured to the front panel, flopping around loose.

Fortunately, I still have the three Flick Drive assemblies to continue dismantling for cleaning and repainting of the Indicator Flags on each. Then it is a case of cleaning and polishing the front of the panel to get it to a point it can be reassembled to the Sender chassis.

An interesting observation at this point should be made though, regarding the Flick Drives used on the Wireless Set No. 52.

I do not think calling these Flick Drives a ‘Standard Feature’ on wartime British wireless equipment is entirely warranted, but they were certainly common to many wireless sets, and they appear to have worked reasonably well up to the time the Wireless Set No. 19 came into service, and the shear numbers of 19-Sets in use, quickly revealed the limitations of these drives. The design was sound, but the products chosen for assembly, quickly proved wanting.

The main problem that came to light by 1943 was that with high usage of pre-set Flick Frequencies, the drives eventually began to fail to return to the chosen frequency reliably. In fact, they would start to drift off the pre-set frequencies so badly, renetting to the required frequency became the only way to get the set back where it was supposed to be. The answer for that with the 19-Sets was the introduction of the Crystal Calibrator unit developed by Canadian Marconi.

In developing what became the Wireless Set No. 52, Canadian Marconi built the Crystal Calibrator designed initially for the 19-Set into the Receiver of the 52-Set. And they went further. In reviewing the concerns raised by the Flick Drives loosing the ability to return to their pre-set frequencies with the 19-Set, two problems were identified.

The BUSHES, Dial, Mounting, No. 2 (ZA 14552) were made of machined, cast zinc. This was found to be too soft and wore out easily with prolonged, repeated use. Canadian Marconi switched to a bronze alloy for these BUSHES on the 52-Set.

The second problem was found to be with the two small BRACKETS, Supporting, No. 1 (ZA 14553) located at the outer, upper corners of the Flick Drives. These had typically been made of small folded steel pieces, screwed to the back plate of the drive. In turn, the front panel of the wireless set was then screwed to these small brackets. It was too easy to strip any of the screws in these assemblies, and the sheet steel flexed too much. This combination would eventually allow the Flick Drive to move as a unit behind the panel when flicking between the two pre-set frequencies. Canadian Marconi solved this by switching to solid bronze alloy BRACKETS, welded in place on the Flick Drives intended for the 52-Set.

A third problem was found to be the steel used in assembling the Flick Drives was too soft. CMC upgraded the specs for the steel they used in their Flick Drive Production.

One extra step CMC undertook was to include the FREQUENCY ADJUSTMENT Control directly above the Tuning Dial on the 52-Set Receiver, just in case a pre-set flick frequency was not spot on when returned to, adjusting that Control would find the correct frequency quickly for the Operator.

The attached photo shows the Bronze alloy BUSHES readily on the three Flick Drives and the triangular plated bronze alloy blocks mounted in the upper corners of the drive assemblies.

This is why the manuals for the 52-Set point out that although the drives and parts thereof are common to both the 52-Set and the 19-Set, 19-Set parts should not be used because they are of inferior quality.

David

[David Dunlop]

I spent the morning today disassembling the rightmost Flick Drive assembly…to a point. A pause was then required for some serious reflection.

The two Flick Indicator Flags at the top of each Flick Drive Assembly need to be repainted. The easiest way to do that would be in removing them from the Drives. The problem, when I got to that point, is the two screws securing the Indicator Flags and their host of assorted springs are impossible to get at with even the smallest screwdriver, without removing the components immediately above them. Something I am just not prepared to do.

The leftmost Flick Drive has little directly above it, but what is there cannot be removed. Mainly the lower Cowl Fastener Receptacle assembly that is welded to the chassis.

After studying the problem for a while, I decided it would be possible to carefully cover over the entire front chassis of the Sender, leaving just the six Flick Indicator Flags exposed. In that condition, they can all be stripped of the existing damaged paint and completely repainted. So a huge amount of additional physical disassembly work can be avoided at the expense of slightly more prep work for the actual painting. I got away lucky with that one.

The other noticeable thing coming out of the Flick Drive pieces today was how different the metal pieces look when clean, compared to the corresponding parts in a 19-Set. They are not the usual dull grey Cadmium Plating one is accustomed to, but a rather shiny finish. Clearly different plating has been used (if one was used) and this may be a reflection of CMC’s decision to use a higher grade of steel in these Flick Drive parts compared to what had been used in the 19-Set items.

David

[David Dunlop]

This 52-Set is never short of surprises, large and small.

I have now finished cleaning all three Flick Drive Assemblies on the Sender today. The surprise this time around was fortunately a small one, but interesting none the less.

When I got to the Frequency Dial Drive on the far left side of the Sender and was removing the Lower Flick Arm, I noticed for the first time that it was different from the other two Lower Flick Arms. And from all other five Flick Arms for that matter. They are all the same, just mounted differently if being used as an Upper or Lower.

A closer look at the odd one confirmed it was actually a Flick Arm from a 19-Set. In the first photo attached, you can see the subtle difference. The 19-Set arm is on the left and the 52-Set arm on the right. The difference is in the extreme left tip of the arm.

As you can see, the tip of the 19-Set arm is stepped down from the last mounting hole to the end. On the 52-Set arm, the lower edge of the arm runs full length to the end curve and is cut back at an angle at the top end.

With the 19-Set arm installed, the end of the arm stuck out slightly beyond the edge of the Upper Drive Disc. I do not think this would create any problems in doing so. It might be a different matter, however, if a 19-Set arm was installed as an Upper Flick Arm in a 52-Set. That end-mounting hole near the tip is actually fitted over the central Flick Indicator Flag Spring Hub and the tip plays a role in activating the Flags by means of applying tension to the Indicator Leaf Springs. Different tips would end up applying pressure on these springs at different points and times. I was not interested in exploring that any further, so removed the Lower Flick Arm and Spring assembly from my spare receiver and installed it onto the Flick Drive in the Sender.

Now I have to decide if the Sender Blower Door is the next restoration step, polishing it back to an acceptable paint patina, or switching over to finish fine tuning my recently assembled, new band saw so I can cut the pine boards needed to restore the missing partition in the 52-Set Tool Box.

David