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Old 25-11-19, 04:41
David Dunlop David Dunlop is offline
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Join Date: Feb 2006
Location: Winnipeg, MB
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Default 52-Set Supply Unit Modification Instructions

I thought I might take some time at this point to document the relevant Modification Instructions for the main set Supply Unit. Over the years, I have found many wireless sets with holders for the modification cards mounted to the inner chassis, but the card is no longer contained within. If you want to know what was done to the set in terms of upgrades, this can be frustrating. The only thing you know for certain with an empty card holder is that at least one modification was performed to that particular piece of equipment, the addition of the Modification Card Holder. If no card holder is present (assuming one was not removed), then no modifications were ever done to your equipment.

Modification Instruction No. 1: This simply adds the metal card holder to the large central plate on the top of the Supply Unit Chassis. Nice and simple. See Photo 2 in Post 198 above.

Modification Instruction No. 2: Another simple one. There is a large resister (R38A) at the back of the supply that needs attention. It is located in the lower left corner, viewed from the back of the supply, mounted horizontally, directly above the 3-pin contacts for the Receiver Supply Module. The red lead on the right hand side of the resistor was prone to getting snagged between the supply chassis and the Carrier No. 4, getting the insulation rubbed through and shorting to the chassis. The fix was to take a small piece of electrical tape and secure this lead, either to the adjacent lead, or back on itself to keep it out of harms way. See Photo 3 in Post 198 above.

Modification Instruction No. 4: This is the most complicated of the three modifications that were issued for the 52-Set Supply Unit. It is a two-part modification to prepare the set for operation in Arctic conditions (read ‘Very Cold!’). At this point in time, the first part of the modification would be very hard to verify. It involved removing the grease and oil from the bearings on the two dynamotors and replacing it with lubricants suitable for cold weather operations. The second part of this modification involves the OZ4A valve located in the receiver vibrator supply module. This is a gas filled valve and for the sake of this discussion, its working conditions are very similar to those of a florescent light tube. If it gets too cold, an OZ4A will not fire properly so the receiver supply will shut down. To solve this problem, a large resister was installed in the receiver vibrator supply. It was mounted underneath the receiver supply chassis, one end soldered to the Pin-2 terminal of the OZ4A socket and the other end to a grounding ring lug, mounted underneath one of the mounting screws of an adjacent transformer located on the nearby side of the chassis. See the attached photo. The resistor in question is the large, black one; oriented diagonally, roughly dead centre in the photo. Once this resister was installed, a 6X5GT could be installed to replace the OZ4A in cold conditions and the vibrator supply would be quite happy regardless of how cold it got. I believe an OZ4A could still be used with this modification in place. Just don’t take the 52-Set camping in Alert in January.

So, hopefully, if you own a 52-Set Supply Unit with an empty Modification Card Holder inside it and you can find these changes to your Supply Unit, you now know these mods were done.

David
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