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Old 21st November 2005, 11:49 PM   #1
Rocky is offline Rocky  Norway
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Default Mains transformer orientation

Hoi. Sorry for boggeling you guys with such a basic question but I am building a very small spud amplifier, and the layout is so compact I worry it might hum easily.

I have attached a model of the amp with the main's trafo bells pointing towards a shielded OPT, it is then pointing sideways to the rectifier tube. Should I leave it like this, or should I turn it around with the bells facing the rectifier (perhaps a better idea since the OPT is shielded?)?

Thought I'd better ask advice before drilling instead of drilling twice.
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Old 22nd November 2005, 12:24 AM   #2
Enzo is offline Enzo  United States
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You want to know what the lamination orientation is in the potted trannies. Mount the power tranny so the laminations are at right angles to the output tranny.
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Old 22nd November 2005, 12:36 AM   #3
Rocky is offline Rocky  Norway
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OK, Gotcha. Should I perhaps put the power tranny in the middle too then, so all xformers will have opposite orientation to the next? Like this..
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Old 22nd November 2005, 12:49 AM   #4
Sheldon is offline Sheldon  United States
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I did a little pp amp with just that orientation. Less than 1mv hum, even with all AC filaments. Actually, mine were all rotated 90 degrees from what you show, but if I understand Morgen Jones's diagrams, what you show might be a little better.

Sheldon
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Old 22nd November 2005, 02:50 AM   #5
Rocky is offline Rocky  Norway
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How 'bout the chokes.. I have two unpotted PSU chokes that goes under the chassi, see attached picture. Any advice for these?

Thanks for all the help
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Old 22nd November 2005, 03:05 AM   #6
Rocky is offline Rocky  Norway
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This way they will have 90deg angle but they get scary close to the signal tubes... I will also have to fit two more irons but they are small mumetal-potted lundahl inputs so I think this is the last orientation concern... thoughts?
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Old 22nd November 2005, 04:25 AM   #7
Rocky is offline Rocky  Norway
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I think this will be it. I pulled the rectifier a little back, the signal tubes a little forward. I'll check the orientation on the Tangos first so I can decide orientation of mains tranny, and then I'm off drilling chassi. Chassi will be 1mm copper - nickel plated at the school lab, so if nickel plating is to happen before christmas, I will have to make the chassi within a week or so. Iron is on it's way from all over the world, so it looks like christmas holydays will be rewarding this year. I plan to go for european rectifier (some majestic looking Telefunken mesh) and the active device will be 6S45P-e delivering just below a watt. Lundahl input iron, and battery bias.

My next weeks is booked with exams so not much building progress is going to happen before holydays starts in mid december, but I'll post some pictures later on as the project evolves. If any wizeguys has something clever to say about the layout, please speak now

This is the CAD-drawing of how the semi-final result looks:
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Old 22nd November 2005, 06:12 AM   #8
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In your previous illustration of the top view, you had the mains tranny laminations pointed at 90 degrees to the OPTs. In the seconnd illustration, it seems to be pointed directly toward them. I think the first one would be better.
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Old 22nd November 2005, 07:22 AM   #9
Rocky is offline Rocky  Norway
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Ray,

I am unsure about the orientation of the Tango trannies. For some reason I assumed they are oriented sideways, can't really say why. Anywayz, I came up with a solution; I slightly adjusted the hole spacing so that the Hammonds can be mounted either way. This way I can just scope the hum and choose the favorable orientation. I will take notice of your advice though, I'll try it sideways first (I will be building during christmas, and I only have access to scopes and signal generators on the electrolab at school, so I will not be able to measure until January)
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Old 22nd November 2005, 09:39 AM   #10
dhaen is offline dhaen  Europe
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Default A suggestion....

Apply mains to the mains trans primary (carefully insulating secondary leads).
'Scope an OPT primary: tweak orientation for minimum signal.

The chokes should be mounted in a 3rd plane. If they don't have suitable mountings for this, make a couple of 90 deg brackets.
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