2 Toroids = 1 Isolation Transformer?

duganj · 30th April 2010, 08:40 PM

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

badman · 30th April 2010, 09:28 PM

For your purpose, yes. For noise rejection, not so much- toroids have high primary/secondary capacitance.

jcx · 1st May 2010, 02:13 AM

line regulation will likely be poor also but it is a practical approach

rjb · 1st May 2010, 02:53 AM

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.

jfitz57 · 1st May 2010, 03:08 AM

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

jfitz57 · 1st May 2010, 03:28 AM

Oh yeah, don't forget to ground that extra wire

.
Not really, just joking.

Jim

jfitz57 · 1st May 2010, 03:52 AM

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

duganj · 3rd May 2010, 11:26 PM

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.

30th April 2010, 08:40 PM	#1
duganj diyAudio Member Join Date: Aug 2005 Location: Portland, OR	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

30th April 2010, 09:28 PM	#2
badman Custom Title diyAudio Member Join Date: Sep 2003 Location: Sunny Tustin, SoCal	For your purpose, yes. For noise rejection, not so much- toroids have high primary/secondary capacitance. __________________ I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

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1st May 2010, 02:13 AM	#3
jcx diyAudio Member Join Date: Feb 2003 Location: ..	line regulation will likely be poor also but it is a practical approach

1st May 2010, 02:53 AM	#4
rjb diyAudio Member Join Date: Jun 2004 Location: Piha	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.

1st May 2010, 03:08 AM	#5
jfitz57 diyAudio Member Join Date: Mar 2010 Location: Western Massachusetts U.S.A.	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

1st May 2010, 03:28 AM	#6
jfitz57 diyAudio Member Join Date: Mar 2010 Location: Western Massachusetts U.S.A.	Oh yeah, don't forget to ground that extra wire . Not really, just joking. Jim

1st May 2010, 03:52 AM	#7
jfitz57 diyAudio Member Join Date: Mar 2010 Location: Western Massachusetts U.S.A.	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

3rd May 2010, 11:26 PM	#8
duganj diyAudio Member Join Date: Aug 2005 Location: Portland, OR	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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