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Mains transformer orientation
Mains transformer orientation
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Old 22nd November 2005, 11:31 AM   #11
Bryan is offline Bryan  United States
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Rocky,

What software package did you use to model the chassis layouts? It seems like a great way to pre-plan the specifics of layout in th final form (though some real world tweaking is always necessary).

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Bryan
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Old 22nd November 2005, 01:36 PM   #12
Sherman is offline Sherman  United States
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Rocky,

One other thing if it isn't too late. I would also mount the OPTs at 180 degrees from each other. If for instance the tab for the B+ on the OPT closest to the PTX is on the same side as the PTX then turn the other OPT so that its B+ tab is closest to the edge of the board.
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Old 22nd November 2005, 05:30 PM   #13
Rocky is offline Rocky  Norway
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Quote:
Originally posted by dhaen
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.

See the attached picture.. looks good? Thanks!

Quote:
Originally posted by Bryan
Rocky,

What software package did you use to model the chassis layouts? It seems like a great way to pre-plan the specifics of layout in th final form (though some real world tweaking is always necessary).

Thanks,

Bryan
I am using SolidWorks 2005. We actually have lessons in it on school. Very nice to visualize many things before building.. After christmas, we're even supposed to get a part printer capable of printing out actual parts made from some powder stuff... Very cool.

Quote:
Originally posted by Sherman
Rocky,

One other thing if it isn't too late. I would also mount the OPTs at 180 degrees from each other. If for instance the tab for the B+ on the OPT closest to the PTX is on the same side as the PTX then turn the other OPT so that its B+ tab is closest to the edge of the board.
I will try with uniform orientation at first. For asthetic reasons. The tangos looks much better that way me thinks.
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Old 22nd November 2005, 08:18 PM   #14
Johan Potgieter is offline Johan Potgieter  South Africa
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Somewhat more.

I presume you are using a CLC type PS filter; chokes look a little small for L-input. In such a case I never really had any effect ever from choke field interference, however mounted.

Power transformer-wise I would go with dhaen's suggestion, if at all practical; only hope you do not get stuck with a funny orientation. Much will depend on the construction of the transformer. Also perhaps note if you do not know, that stray field induction in an unloaded output transformer is far worse than in a loaded (i.e. with circuit powered up) one, because of the damping effect of the loudpseaker and valves. This is especially true if you use UL or triodes. But you should be OK with a copper chassis. (Not to be alarming, but I recently had a whopper of a problem trying to "cure" power transformer induction on a steel chassis. Best position was at a 50 degree angle - I had to abandon in the end and go to alu.)

Keep us posted of your findings.
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Old 22nd November 2005, 08:29 PM   #15
dhaen is offline dhaen  Europe
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Quote:
I presume you are using a CLC type PS filter; chokes look a little small for L-input. In such a case I never really had any effect ever from choke field interference, however mounted.
That's not the main problem IMO. It's the pickup of mains transformer field in the chokes, causing more ripple than expected; and of a strange shape.
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Old 22nd November 2005, 08:54 PM   #16
Johan Potgieter is offline Johan Potgieter  South Africa
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dhaen,

No, OK, point taken, although there are often questions regarding the orientation of the choke simply because it is seen as a possible source of magnetic field.

But interesting point: At first consideration I would imagine that especially in a CLC filter, the choke would be so "shunted" by the capacity across it as to be rather insensitive to external fields. Something to investigate next time I hook up such a circuit. Have you experienced something in the line of what you mentioned?
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Old 22nd November 2005, 09:27 PM   #17
Rocky is offline Rocky  Norway
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The filter is indeed CLC. 22uF BG VK to split channels - 30H - 150uF BG VK. To simplify initial construction, I'll probably install the chokes without the brackets at first. When I do make the brackets, I'll compare the measurements.

I had not thought of the chokes picking up the field from the mains tranny. But in this sense, as I get it, the 90deg angle between the chokes is of (much) less importance than the 90deg angle vs the mains tranny, given a CLC filter topology, as the magnetic interference between the chokes would be minimal?
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Old 22nd November 2005, 09:28 PM   #18
dhaen is offline dhaen  Europe
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Default Hum induced into choke

Johan,

Quote:
Have you experienced something in the line of what you mentioned?
I'm sure I have, but I am having trouble sifting through the "rubble" of my memory to remember the details. I can't even remember the configuration (LC, CLC) for sure..

I'll keep thinking.
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Old 23rd November 2005, 02:13 AM   #19
Sherman is offline Sherman  United States
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Quote:
Originally posted by Rocky



...I will try with uniform orientation at first. For asthetic reasons. The tangos looks much better that way me thinks.

Actually I agree! I wish the logo tags could be easily turned around! If it sounds good with them both oriented the same way use them that way.
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Old 23rd November 2005, 02:50 AM   #20
Tubelab_com is offline Tubelab_com  United States
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"Also perhaps note if you do not know, that stray field induction in an unloaded output transformer is far worse than in a loaded (i.e. with circuit powered up) one, because of the damping effect of the loudpseaker and valves. "

I found this out the hard way. The amplifier shown on my home page had this funny hum that appeared on power up, and disappeared as the rectifier tube warmed up, and plate current began to flow. The hum was even present with the output tubes removed, and did not go away (no plate current).

When I brought the amp over to a friends house who has speakers that are 10 db more efficient, it became obvious that the hum didn't go away, it just got a lot quieter. Rotating the power transformer 90 degrees solved the problem.

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