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Old 27th August 2012, 04:55 PM   #1
pilovis is offline pilovis  Italy
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Default Lowering cost of SE audio output transformer

Given that the cost of S.E. audio transformers has become prohibitive, I'm trying to use modified line transformers at place of class A audio transformer.

Laminated core as shown below with insulating paper between the two groups of laminations:

Click the image to open in full size.

Primary winding divided into two only sections, the same for the secondary, wound according to the following scheme:

"First section primary, secondary first section, second section primary, secondary second section."

Examples:

5K/8ohm transformer (6V6, EL34, ECL86, EL84, KT88 - S.E.) = 110+110 Vac primary - 4.5+4.5 Vac secondary
3K/8ohm transformer (6L6, 807 - S.E.) = 110+110 Vac primary - 6+6 Vac secondary
800/8ohm transformer (EL/PL504 - S.E.) = 110+110 Vac primary - 12+12 Vac secondary

This construction and winding scheme (standard voltages) greatly reduces the cost of the transformer (I pay for it only 15 Euro for a 40 VA custom transformer).

The first two prototypes will be available in two days so I will test them to see if they work (hope so...)

Last edited by pilovis; 27th August 2012 at 06:12 PM.
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Old 27th August 2012, 04:58 PM   #2
GCA is offline GCA  United States
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That could be interesting.
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Old 27th August 2012, 05:05 PM   #3
kevinkr is offline kevinkr  United States
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I'm quite sure it will be very interesting.

Toroidal power transformers have a good track record in PP and parafeed applications with tubes having extremely low rp like the 6AS7/6080..
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Old 27th August 2012, 05:16 PM   #4
TheGimp is offline TheGimp  United States
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PP or SE transformers?
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Old 27th August 2012, 05:22 PM   #5
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by TheGimp View Post
PP or SE transformers?
SE transformers, PPs do not have direct current saturation so do not need special insulated core as shown above.
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Old 27th August 2012, 05:54 PM   #6
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Quote:
Originally Posted by pilovis View Post
SE transformers, PPs do not have direct current saturation so do not need special insulated core as shown above.
I thought mains transformers had no gap. Are these being built with or without a gap??

Cheers

Ian
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Old 27th August 2012, 05:59 PM   #7
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Of course they will be built with a gap....The fun experiment will be setting the gap...I always thought one could use a roll of Teflon tape to experiment with gapping..

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Old 27th August 2012, 06:02 PM   #8
pilovis is offline pilovis  Italy
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Quote:
Originally Posted by ruffrecords View Post
I thought mains transformers had no gap. Are these being built with or without a gap??

Cheers

Ian
As you can see on the above picture there is a gap between "E" laminations and "I" laminations, insulated with paper.

Last edited by pilovis; 27th August 2012 at 06:10 PM.
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Old 27th August 2012, 06:03 PM   #9
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Thread title:

Lowering cost of SE audio output transformer

Suggested thread title:

Making good SE output transformers at lower cost

Reason: price should not be the only driving factor. Quality is prevalent in audio DIYing since the device will be more expensive than ready built devices anyway.
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Old 27th August 2012, 06:10 PM   #10
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I actually still don't understand what you are you doing. Are you just ordering a special version of a standard model transformer from a manufacturer, i.e. you instructed them to build you one of their standard power transformer models except to create a gap using paper? Or do you have a transformer in hand that you took down to the laminations without destroying the bobbins and are reassembling it with a gap?
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