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Old 7th January 2007, 12:52 PM   #1
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Default Series connecting output Transformers.

In my pursuit of high end hi-fi on the cheap I was trying to work out if it was possible to get higher impedance matching of transformers by connecting two in series. This would be in a PP amp so the primaries would have to be cross coupled to get current balance in the two series connected transformers. All the secondaries of the two transformers would be connected in parallel.
The reason that this would become useful for me is because it would allow me to develope a 5K transformer out of two 6V mains toroidal transformers.

What do you think.

Shoog
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Old 7th January 2007, 01:01 PM   #2
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In principle it would work, but a normal mains transformer does not have an airgap. When the dc current is too high the transformer could be saturated and than there is no impedance left.
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Old 7th January 2007, 01:45 PM   #3
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I will use CCS sources on the cathodes of the output Valves in order to ensure current matching. I have used this setup in my current 6080 amp and it works very well with single toroidals.

Shoog
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Old 7th January 2007, 02:12 PM   #4
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Can you post a schematic diagram ?
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Old 7th January 2007, 06:02 PM   #5
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I did a sketch I will scan it in and post it.

Shoog
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Old 7th January 2007, 06:13 PM   #6
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Ok, I will wait and looking for it.
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Old 7th January 2007, 07:04 PM   #7
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DC flux in transformers will be a problem. It cancels if two equal opposing currents are in the SAME core.
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Old 8th January 2007, 12:10 AM   #8
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Hey Shoog, I love all of the work you're doing with 'off the shelf' toroids. Keep it up. The idea of trying to balance the PP currents in a toroid scares the hell out of me, but if you make it work then more power to you!

Anyway, series connecting (identical) transformers will double the inductance. Another way to look at it is that the AC voltage across each will be half of a single unit.

-- Dave
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Old 8th January 2007, 12:20 AM   #9
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Heres my idea.

Quote:
Hey Shoog, I love all of the work you're doing with 'off the shelf' toroids. Keep it up. The idea of trying to balance the PP currents in a toroid scares the hell out of me, but if you make it work then more power to you!
With single toroidals getting the DC standing current balanced is simply a matter of putting matched CCS's in the cathodes of the output tubes. Since this will improve the performance of standard PP transformers it seems stupid not to use it everywhere possible.

Shoog
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Old 8th January 2007, 10:01 AM   #10
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This could work, because the dc current is compensated. I only do not know how it sounds, because of it's lower selfinductance the lower tones could be missing.
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