View Single Post
  #152  
Old 17-04-19, 22:57
David Dunlop David Dunlop is offline
Registered User
 
Join Date: Feb 2006
Location: Winnipeg, MB
Posts: 3,384
Default Handles No. 72 and Clamping Screws Replacement

This past weekend, I was able to replace the Handles, No. 72, and its related Screws, Clamping No. C2, on the Tuning Dial of my Main Set Receiver. Their original look can be seen in the left hand photo in Post 149 of this thread.

I had mentioned in an earlier Post that the Handles unit was badly chipped and dented and the Clamping Screws were really showing their age now. So replacing them all with the ones from my spare receiver made a lot of sense. A side project spun off of this related to the Slow Motion Drive Assembly on the Main Set Receiver, but I will deal with that in a separate Post shortly.

Any work on the tuning dials of the 52-Set (or even the 19-Set and any other wartime wireless equipment using this style of tuning dial) can be a very intimidating task. The four Clamping Screws operate the Flick Mechanism that enables the Wireless Operator to preselect two different operating frequencies, that once set, can be dialled in very rapidly. These are the ‘A’ and ‘B’ (Red and Blue) frequencies highlighted on the front panel of the wireless set. Typically, one frequency would be for daytime use and the other for nighttime.

To make all of that work, there are four separate components behind the Handles, the Clamping Screws pass through or screw into. Two of these pieces are Washer, Clamping, Front and a Washer, Clamping Rear. The 19-Set Manual refers to these as ‘Plates’ for some reason. I have added a photo of the Washer, Clamping, Front.

There is a bit of free play as to how these two pieces sit in the tuning assembly. They can move around a little and it only takes a little movement for the holes to shift out of alignment once the Clamping Screws are removed. So you do not want that to happen. You want gravity to work for you, not against you when doing this work and to that end, I would strongly recommend you lay the receiver on it’s back, on a couple of supports to protect the rectangular connector on the back. Once the receiver is lying flat on its back all the fiddly bits will stay put. If you are still nervous about doing this work, another great tip I got from Jacques Fortin, is to get hold of an early version of the Clamping Screws used on the Mark II Wireless Set No. 19: The straight ones with the slot in the end. These were designed and intended to allow the Handles No. 72 to be removed and replaced without losing the hole alignments inside the Flick Mechanism. Simply installing one of these older Clamping Screws and running it home will prevent serious hole misalignment.

To remove the Handles No. 72, first unscrew the grub screw on the lower side of the handle. This will require a small jeweller’s slotted screwdriver, not a Bristo or Allan Key. Then unscrew and remove the large screw in the centre of the Handle No. 72. Then comes the tricky bit.

There is a pair of Springs, Steel, Wire No. 1 (ZA 14271) located in slots on either side of the Handles No. 72. These springs were designed to put tension on the sides of the Clamping Screw shafts to prevent them from accidentally falling out of the Handle if they were completely unscrewed. There is a very small pivot pin located centrally along each Spring. These create the tension against the Clamping Screws when they are installed in the handle. When the tension is gone (the Clamping Screws removed from the system) these small pivot pins are free to fall out of the bottom of the Handles No. 72 when you try lifting it off the tuning dial. To prevent this from happening, grab the ends of one Spring with the index finger and thumb of one hand and do the same with the other hand on the other spring. Then pull the ends of both springs outward slightly from the centre of the Handle, while maintaining enough grip on the handle to lift it clear of its mounting shaft. As it comes clear, keep the tension on the springs and turn the Handle No. 72 on its back before putting it down on your workbench. This will keep the pivot pins safely in their two holes. See the attached photo of the back of the old Handles No. 72 I replaced. The two holes are at the ‘9’ and ‘3’ positions and clearly these pins have been lost more than once over time with my spare receiver. The one at ‘3’ is too long and the end of the pin shaft has been punched to permanently retain it. The pin that came out of the ‘9’ position is not an original pin but a section of screw shaft cut down to fit. Wow! The stories parts can tell sometimes.

For reassembly, make sure the holes for the four Clamping screws all line up. A small knitting needle can be used to tweak any slightly. From it’s upside down position on your workbench, do the same finger trick with the tension on the springs to pick it up and turn it over to drop onto its shaft. Only release the tension when it is down all the way. It is a good idea at this point to replace the four Clamping Screws. There will be a slight bit of resistance when the screws first encounter the spring but they easily push past that point. When you know they are all run home, replace the large central screw. Once the Handle No. 72 is fully seated, retighten the grub screw.

Last photo is the Main Set Receiver with the nicer looking Handles No. 72 and Clamping Screws installed.

And that’s all she wrote this time,

David
Attached Thumbnails
Handles, No. 72 Assembly and Washer, Clamping, Front Assembly.JPG   WS No. 52 Main Set Receiver Refurbished Tuning Dial.JPG  
Reply With Quote