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Old 16th February 2006, 11:48 PM   #1
Trout is offline Trout  United States
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Question PT/OPT Orientation questions

Hi Guys,

I have a question about power transformers, To be specific, Orientation of the PT in relationship to the Output Trans & The Copper band that surrounds the PT plates.
#1, Is the copper band a directional isolation thing? This particular PT is a thru chassis mount. I am mounting it to a 17X10X3 Steel Hammond chassis. 360V CT 200ma, w/50V bias tap, 5.0V-3A and 6.3-4A.
Its going into a guitar amp which of course is notorious for high gain related issues.
#2, Are steel chassis a bad idea in this type of environment? I noticed a lot of amps use aluminum, Is this to avoid magnetic issues? I have had my fair share of home brew oscillators (guitar amps) and hope to avoid this in the future and wonder if this is a contributing factor.
#3, Seeing as this is a thru-chassis mount type PT, What is the rule of thumb in determining OPT orientation ? The opt is a normal upright type with mounting tabs on each end similar in shape to a Hammond 125E just a bit larger and rated for 35-40W.
Trout
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Old 17th February 2006, 01:08 AM   #2
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My knowledge of magnetics is limited, but maybe I can help a little...

1. The copper band is essentially a shorted single turn around the transformer windings. Its intent is to limit the strength of the magnetic field outside of the transformer's core, and for your application, this is a good thing!javascript:smilie('')
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2. I don't know about steel chassis, good or bad, I've seen both steel and aluminum used successfully in tube electronics. javascript:smilie('')
headscratch

3. If I were you, I'd try a little experiment. Mount your PT as you describe it, insulate the secondary leads, and apply power across the primary. Connect a winding of your OPT to the input of one of your other amplifiers, and move the OPT around on the chassis to see where the hotspots and quiet spots are.

Just some thoughts. I hope this helps!

Fuzzbrain
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Old 17th February 2006, 04:12 AM   #3
Trout is offline Trout  United States
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Hey Fuzzbrain

Sounds like a good plan, I have heard, that its possible to attach headphones to the OPT and move it around in a similar fashion, Invisible noises always bite me lol

My last couple amps have been just on the edge and I really want to clean up this issue, So I am trying to cover all the possibilities
Trout
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Old 17th February 2006, 04:52 AM   #4
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Just make sure that the PT laminations are perpendicular to the OT laminations. In general a thru chassis mounting PT will mean that its laminations are parallel tot he chassis top so the OT laminations will be automatically perpendicular to them and its orientation (front to back or left to right) won't matter a rodents hind quarters.

Cheers,
Ian
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Old 17th February 2006, 01:50 PM   #5
Trout is offline Trout  United States
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Quote:
Originally posted by gingertube
Just make sure that the PT laminations are perpendicular to the OT laminations. In general a thru chassis mounting PT will mean that its laminations are parallel tot he chassis top so the OT laminations will be automatically perpendicular to them and its orientation (front to back or left to right) won't matter a rodents hind quarters.

Cheers,
Ian
Thanks! That was what I was Hoping
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Old 17th February 2006, 11:34 PM   #6
BARR is offline BARR  Europe
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transformer placement
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