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Author Topic: Unknown Thordarson transformer  (Read 4413 times)
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n4joy
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« on: March 29, 2020, 12:35:46 PM »

Hi!  I spent the better part of my day yesterday attempting to identify a Thordarson transformer marked T53475.  I looked through numerous catalogs online but no luck.  The rubber insulation of the wiring is rotted.  Before I do anything with it, it would be nice to identify it.  My bet is 1800 to 2000vct and 200-300ma.

Perhaps someone has access to a catalog that is not online?

Thank you!!!


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W4AMV
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« Reply #1 on: March 29, 2020, 12:51:35 PM »

Hi Chris,

Identify what you believe is the secondary wire(s). Usually, red and red/yellow stripe if CT. Get a DC measure of the R value of the secondary and the CT would be half that value. That will provide a clue of the current handle capability.

Then if you have an audio oscillator or simply a 120 variac, apply a LOW primary V, say 5 V and take a measure of the secondary V. That will give you the turns ratio and help verify if it is 1800 V or whatever... without causing arc over to the frame or the iron if there is an issue.
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WZ1M
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« Reply #2 on: March 30, 2020, 02:34:12 AM »

Resistance each side of the center tap will NOT be the same. Turns will be the same, not resistance.
Regards,
Gary
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W4AMV
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« Reply #3 on: March 30, 2020, 05:40:30 AM »

Correct. I should say as a check the sum of the resistance values each side of C.T. should be the same as the reading across the whole HV winding.

Example, I looked at a Stancor PC8414 rated at 600-0-600 V at 200 mA.
The C.T. to end winding for each is 66.6 and 73.4 ohm.
Reading the whole H.V. winding is 140.3 ohm.

The intent here was a sanity check to be sure the  winding under test is a HV winding with CT as compared to filament with C.T. or some other odd arrangement.
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KA2DZT
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« Reply #4 on: March 30, 2020, 09:53:53 PM »

Five digit part numbers were specials, not regular catalog xfmrs.

Thordarson made thousands of different xfmrs.  Ones with five digit numbers were made special for some maker of some piece of equipment, only Thordarson and the equipment maker had the info on the xfmr.

Looking at the pics,  unlikely it is 2kv at 200-300ma.  Depends on how many wires are coming out of it.

Fred
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WZ1M
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« Reply #5 on: March 31, 2020, 02:37:04 AM »

Apply 10vac to the primary with a variac and monitor the current draw. With this voltage on the primary, you should get some idea of what the secondary voltage would be. After being in the transformer business for 25 plus years, I would say what you got there is more in the line of 400 to 500 volts, CT @ 200 mils. I bet the primary is only 115vac.
Regards,
Gary
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n4joy
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« Reply #6 on: March 31, 2020, 06:39:31 AM »

I appreciate all the replies.  The information is most helpful.  Here is another picture of the transformer from the side. 


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WZ1M
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« Reply #7 on: April 01, 2020, 03:56:00 AM »

How many leads coming out of it?
Regards,
Gary
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n4joy
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« Reply #8 on: April 01, 2020, 12:57:37 PM »

Hi, Gary.  Two black wires on the primary side and three for secondary (red, red, and red/yellow for CT).  I haven't applied power via a variac yet. 

How many leads coming out of it?
Regards,
Gary
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WZ1M
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« Reply #9 on: April 01, 2020, 02:23:19 PM »

Yep, just a plate or bias transformer. My guess is plate but not that high of voltage.
Have you tried putting 10 or 20 volts on the primary?
Regards,
Gary
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n4joy
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« Reply #10 on: April 01, 2020, 09:00:12 PM »

Gary,

I am seeing approxomately 300V across the secondary at 20V on the primary.

Chris
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KA2DZT
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« Reply #11 on: April 02, 2020, 01:47:06 AM »

A plate xfmr, about 1800vct with 120v in.  I have all the Thordarson catalogs here, don't remember ever seeing a plate xfmr with this voltage and case style.

Thordarson made thousands of xfmrs.  They would make a new line of xfmrs almost every year with new part numbers.   OTOH Stancor made the same xfmrs year after year with the same part numbers.

Fred
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W4AMV
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« Reply #12 on: April 02, 2020, 08:44:36 AM »

Gary,

I am seeing approxomately 300V across the secondary at 20V on the primary.

Chris

Chris,

Take a measure of the total R of the secondary to get an idea of the current capability. How much does the former weigh?

73' Alan
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AG5UM
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« Reply #13 on: April 02, 2020, 08:53:01 AM »

Once you know the Voltage ratio, then you know the Turns ratio, then you know the Impedance ratio.
(those little formulas, Vs/Vp=Ns/Np, Zp/Zs=Np2/Ns2)
Which I'm sure you already know,
...just thinking outloud...
Then you can look up the plate resistance,etc. for the tube you are using, etc. ,etc.
Of course, current ratings, internal shielding-transformer design considerations all add to the picture, as you already know.
I'm glad people have saved the old catalogs, it really helps,
Good luck,
AG5UM
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