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Modulation transformer for UM-1




 
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Author Topic: Modulation transformer for UM-1  (Read 416 times)
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ns7h
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« on: October 12, 2022, 12:53:26 PM »

I have a WRL Globe Chief I want to add AM via the UM-1 modulator.  I picked up a "UM-1" in chassis only condition at a hamfest.  The unit had been modified to a design from the 1955 Handbook using a 6SJ7, 6SN7 audio into a pair of 6L6s instead of a 6U8.  The power transformer, choke, and modulation transformer have been also changed and downrated to a 25 watt modulator since the mod transformer (Thordarson T-19M14) is rated at 25 watts.

I would like to restore this "chassis" to an original UM-1 since I have a full documentation package and kit instructions.  I can rebuild from scratch, but I would like to find the modulation transformer that was part of the original design or functional physical equivalent (45 watts, 500 to 20000) ohms impedance with variable taps.)  The documentation did not give the manufacturer or model number for the transformer.


I have been looking at Thordarson mod transformers and a few others on ebay, but I also want to keep within the original foot print for the chassis.  The mounting holes for the chassis (original ) are about 3 3/8 inches on a side.

Anyone have an original UM-1 with original mod transformer that can share make, model, year?  that I can use to focus a search for a replacement at the right power level 45-50 watts?

I appreciate any of you collectors/users than can provide this information.

73, Bob, NS7H
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K0VGD
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« Reply #1 on: October 14, 2022, 11:48:00 AM »

Bob,

The only markings I see on the mod transformer of my UM-1 is the WRL part number (1203-008) and 839738. Both are stamped into the end bell on one side. I can send pics of everything if you'd like.

73, Bob/K0VGD
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w9jsw
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« Reply #2 on: October 15, 2022, 07:21:39 AM »

There is a guy on ebay selling globe champion parts. Maybe contact him to see if he has that transformer? He is currently selling the 1203-006 driver transformer and a plate transformer.

https://www.ebay.com/itm/313932779384
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ns7h
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« Reply #3 on: October 16, 2022, 11:50:17 AM »

Thanks for the replies.  The part number is useful to see if any mod transformer is from a globe.  The champion mod transformer I will have to look up.  The Thordarsen transformer catalogs have what I believe could be a direct replacement for the UM-1 unit at the same footprint and 45-50 watt level.  Some on ebay have been rode hard and put away wet for a premium price.   But now I think I can start roaming hamfests and other AMers for a replacement. 

Thanks again

Bob. NS7H
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KA2DZT
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« Reply #4 on: October 16, 2022, 01:31:06 PM »

Bob,

The only markings I see on the mod transformer of my UM-1 is the WRL part number (1203-008) and 839738. Both are stamped into the end bell on one side. I can send pics of everything if you'd like.

73, Bob/K0VGD

The six digit number is a date code and maker number.  839 should be the maker of the xfmr.  These date codes were use mostly in the 50s and 60s.  the 738 should indicate the xfmr was made in the 38th week of 1957 could be 1967,  you have to figure that out based on the unit that the xfmr came from.

you can google date codes and find out more  look up which maker was 839

Fred
KA2DZT
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