Using UL taps instead of the anode taps to alter inpedence - diyAudio
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Old 8th July 2014, 03:34 PM   #1
kanks is offline kanks  United Kingdom
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Default Using UL taps instead of the anode taps to alter inpedence

Ive got a quick question. If i have a Ultra linear transformer with say a 12k primary and 50% UL taps could the UL taps be used to half the primary independence.
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Old 8th July 2014, 03:42 PM   #2
disco is offline disco  Netherlands
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No doubt. If you want to check measure the turns ratio (from primary UL tap to secundary).
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Old 8th July 2014, 03:47 PM   #3
kanks is offline kanks  United Kingdom
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Its more theoretical at the moment as Ive got some transformers here that I would like to use with EL34 tubes but the primary impedance is a little on the high side going by the RCA manual.
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Old 8th July 2014, 03:47 PM   #4
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The 50% for the UL taps refers to the turns ratio, but the impedance is proportional to turns ratio squared, so 12k x 0.5 x 0.5 gives 3k.
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Old 8th July 2014, 03:51 PM   #5
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You forgot the square term, half the primary turns results in a quarter of the primary impedance, also by not using the full winding of the OPT, the frequency response is likely impacted as well.
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Old 8th July 2014, 03:51 PM   #6
kanks is offline kanks  United Kingdom
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Quote:
Originally Posted by Malcolm Irving View Post
The 50% for the UL taps refers to the turns ratio, but the impedance is proportional to turns ratio squared, so 12k x 0.5 x 0.5 gives 3k.
Excellent point. I'm looking at doing a push-pull el34 and thinking a of using the UL taps on a transformer to get into the ball park for 4 el34 tubes. I'm just confusing myself I think by thinking like this.
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Old 8th July 2014, 04:06 PM   #7
disco is offline disco  Netherlands
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Giving it more thought will there be enough self inductance left, using only part of the winding?
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Old 8th July 2014, 04:31 PM   #8
DF96 is offline DF96  England
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At half the winding you will get a quarter the impedance match and a quarter the inductance, so the frequency balance will be the same. You will get half the winding resistance, so a small loss of efficiency.

An extra issue is heating. You might want to run with twice the DC or signal current, but this will give you twice the heating so you may need to derate the transformer.

Last edited by DF96; 8th July 2014 at 04:32 PM. Reason: mention heating
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Old 8th July 2014, 04:45 PM   #9
kanks is offline kanks  United Kingdom
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Well im gonna give it a go and ill let you know how I get on.
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