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Old 7th July 2003, 05:05 PM   #1
Guiness is offline Guiness  United States
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Default transformer mounting...

I was wondering if you could mount a Hammond enclosed filament transformer next to a hammond enclosed power transformer without the introduction of noise (hum). I know a choke next to a power transformer is a no no, just wondering if the same applied with a 14V 4A filament transformer.
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Old 7th July 2003, 05:13 PM   #2
Joel is offline Joel  United States
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Default Re: transformer mounting...

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Originally posted by Guiness
...I know a choke next to a power transformer is a no no...
What do you mean? I've done that many times. Really close too, like 10mm away.
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Old 7th July 2003, 05:32 PM   #3
Guiness is offline Guiness  United States
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So have I... I am basically going by what people say. Just trying to figure out what some poeple have experienced.
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Old 7th July 2003, 05:45 PM   #4
EC8010 is offline EC8010  United Kingdom
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Default Bucking hum

Putting a choke next to a power transformer would only be a problem if the two coils were aligned and the choke was part of a CLC filter where the filtering was so good that the output ripple was expected to be very small. Even then, I doubt if there would be a signficant problem, and if it was, reversing the choke connections would actually improve matters by bucking the remaining hum.

As for problems with putting two power transformers close together, they're both producing AC anyway, so exactly how can one cause hum in the other?

It's the positioning of output transformers relative to power ironmongery that you have to watch out for.
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Old 7th July 2003, 05:50 PM   #5
Oscar is offline Oscar  Sweden
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Default Re: Bucking hum

Quote:
Originally posted by EC8010
It's the positioning of output transformers relative to power ironmongery that you have to watch out for.
Sorry, do you feel like elaborating a bit more on this? I don't understand at all what you're saying, but I believe it might be possible with a different wording...
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Old 7th July 2003, 06:51 PM   #6
Joel is offline Joel  United States
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He means that you don't want to place a power transformer right next to an output transformer.
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Old 7th July 2003, 07:50 PM   #7
EC8010 is offline EC8010  United Kingdom
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Hello Oscar, my apologies, I shouldn't be colloquial on an international forum.

Transformers couple to each other. Rotating them so that the coil of one transformer is at 90 degrees to the coil of the other greatly reduces coupling. Coupling is also inversely proportional to the distance squared (between transformer centres).

It doesn't matter if a power transformer couples to another power transformer because both transformers carry the same signal. It does matter if a power transformer couples mains hum to an output transformer when that output transformer is supposed to be delivering silence to the loudspeaker. Thus, we should distance output transformers from mains transformers (and to a lesser extent, chokes), and we should ensure that their coils are not aligned.
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Old 7th July 2003, 11:45 PM   #8
EC8010 is offline EC8010  United Kingdom
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Joel, that's short, and to the point (better than my last post).

Surprisingly, you can get away with putting an output transformer next to a power transformer, provided that the coils are at right angles. The Leak Stereo 20 (PP EL84) had < 1/4" gap between mains and output transformers...
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Old 8th July 2003, 02:22 AM   #9
Joel is offline Joel  United States
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Yeah, I'm always AMAZED at the layouts in vintage amps - and they all worked! I mean transformers on top of other transformers, PSU chokes next to inputs, preamp tubes up against output tubes, electrolytic capacitors a half inch from a 5U4 rectifier... funny.

That's why I get a kick out of the beginner questions - "...should I place each piece of iron on a different chassis?"
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Old 8th July 2003, 04:18 AM   #10
EC8010 is offline EC8010  United Kingdom
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Agreed, an innocent's question makes you THINK!
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