2 Toroids = 1 Isolation Transformer? - diyAudio
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Old 30th April 2010, 08:40 PM   #1
duganj is offline duganj  United States
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Default 2 Toroids = 1 Isolation Transformer?

I have a few toroid transformers out of some SS gear, very similar specs to these:

Toroid Audio Amplifier Power Transformer, 220VA, 81v w/ Center Tap

If I hook up two of these back to back will that result in an isolation transformer?

I'm looking to safely operate a tube amp out of an old Kodak projector that has a hot chassis connection.

Thanks,

John
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Old 30th April 2010, 09:28 PM   #2
badman is offline badman  United States
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For your purpose, yes. For noise rejection, not so much- toroids have high primary/secondary capacitance.
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Old 1st May 2010, 02:13 AM   #3
jcx is offline jcx  United States
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line regulation will likely be poor also but it is a practical approach
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Old 1st May 2010, 02:53 AM   #4
rjb is offline rjb  New Zealand
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To clarify comment by jcx, there will be losses in each transformer, both fixed and varying with current drawn. So output voltage drop caused by the changing load will vary more than if a true isolation transformer were used. Check what the output voltage actually is under load. Take care not to receive a shock when doing so.
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Old 1st May 2010, 03:08 AM   #5
jfitz57 is offline jfitz57  United States
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Maybe wire the primary's in parallel and the secondary's in seriese and take the output from one whole secondary + one half secondary? 81+(81/2)=121.5?

Jim
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Old 1st May 2010, 03:28 AM   #6
jfitz57 is offline jfitz57  United States
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Oh yeah, don't forget to ground that extra wire .
Not really, just joking.

Jim
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Old 1st May 2010, 03:52 AM   #7
jfitz57 is offline jfitz57  United States
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If you have three of them wire the primary's in parallel and three half secondayy's in seriese and you have a 660VA iso-former.
Don't forget to connect all the extra wires together and ground them .

Jim
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Old 3rd May 2010, 11:26 PM   #8
duganj is offline duganj  United States
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Thanks for the input.

I wired them up back to back and got my amp up and running. Now I'm trying to overcome some of the 'safety precautions' taken by Kodak for when the amp was running with a hot chassis.

Schematic here:
Kodak Projector Amp Schematic AV-085 on Flickr - Photo Sharing!

I replaced the germanium diodes with 1N4005's that I had around, things are still functioning.

Points L and M are jumpered with 2x6.8 Ohm resistors to replace the ~3 Ohm light bulb. 120V out of the iso-transformer goes in to the other two pins on the power plug.

I grounded the speaker socket to the chassis which helped with some of the noise.

Next I was looking at shorting C-4.
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