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Old 28th February 2013, 07:56 AM   #1
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Default Transformer with strange output- 240V- 5.5mA

Hi all,

I have an unmarked transformer that I got for $5 from a surplus electronics store.

It has four leads- 1 red, 1 black, and 2 white.

I wired the 2 white live and neutral using the red and black as outputs.
The GFI tripped

Red live, Black neutral -white outputs- tested white to white- 0V white to earth/ ground 240V per white lead. White to Earth/ ground 5.5 mA- 4.8mA going through a 22k resistor. A bridge brings it down to 168v - 30v depending on the bridge with 2.4mA. output.

White to live, black to neutral- red and white outputs. tested white to red- 240V white to earth- 0V Red to earth- 240V 5.5mA

I talked to an electrician that agreed that it seemed odd.
Do I have a choke instead of a transformer? Maybe an audio output transformer?

Any answers or suggestions would be appreciated.
I'm making a tube preamp, but I don't think 2.4 mA will run much.

Thanks
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Old 28th February 2013, 09:34 AM   #2
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
use a bulb tester !!!!!
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regards Andrew T.
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Old 28th February 2013, 10:46 AM   #3
Jay is offline Jay  Indonesia
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Join Date: Feb 2003
Location: Jakarta
Do a CONTINUITY TEST to find out the number of separate windings. If all cables are connected then it could be an autoformer. Most of the time it consists of 2 windings. Then one is a "primary" and the second one is "secondary" (could be stepup or step down).

By measuring the resistance (or relative resistance) and looking from the wire size you will be able to predict the physical construction. By measuring the voltage you can also know the relative direction of winding.

Just do a "proper" check and you will be able to find out what it is (I'm confused to visualize what you have done/measured).
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Old 28th February 2013, 07:02 PM   #4
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Join Date: Dec 2010
Quote:
Originally Posted by Jay View Post
Do a CONTINUITY TEST to find out the number of separate windings. If all cables are connected then it could be an autoformer. Most of the time it consists of 2 windings. Then one is a "primary" and the second one is "secondary" (could be stepup or step down).

By measuring the resistance (or relative resistance) and looking from the wire size you will be able to predict the physical construction. By measuring the voltage you can also know the relative direction of winding.

Just do a "proper" check and you will be able to find out what it is (I'm confused to visualize what you have done/measured).
All leads are the same wire size, all leads have continuity with each other.

So this could be an autoformer...but is heavy and large. The winding make up a size larger than my fist.

Can 2.5mA drive a tube preamp? My simulation on Simetrix simulates that only uA's are drawn from the power supply.

Last edited by rcollege; 28th February 2013 at 07:05 PM.
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Old 1st March 2013, 06:46 AM   #5
diyAudio Member
 
Join Date: Dec 2010
Quote:
Originally Posted by Jay View Post
Do a CONTINUITY TEST to find out the number of separate windings. If all cables are connected then it could be an autoformer. Most of the time it consists of 2 windings. Then one is a "primary" and the second one is "secondary" (could be stepup or step down).

By measuring the resistance (or relative resistance) and looking from the wire size you will be able to predict the physical construction. By measuring the voltage you can also know the relative direction of winding.

Just do a "proper" check and you will be able to find out what it is (I'm confused to visualize what you have done/measured).
Thanks Jay,

It is an autoformer
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