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Old 3rd July 2010, 11:35 AM   #11
Pano is offline Pano  United States
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I second the EL84 P-P transformer idea! It would be a great help and a great place to start.
Maybe even a group buy for materials.

Then on to a good SET transformer for the really brave. =)
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Old 3rd July 2010, 11:39 AM   #12
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Did I leave out UL taps
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Old 3rd July 2010, 02:16 PM   #13
M Gregg is offline M Gregg  United Kingdom
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Hello all,

I am surprised at the response from the forum!

I thought a single ended would be an easier transformer to build than PP. I seem to be wrong!

The main point of the post was to try to get arround the Op transformer being such a sticking point.

My thoughts are to build the transformer and then build the amplifier to match. Taking the easy road so to speak!

So for a starting point which is the best option for a first optx SE or PP?
Would it be better to do KT66 PP? Giving more output?
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In the past I have built 8 EL34's running in PP 4 per channel and wanted to build a small good sounding amp!

Any thoughts?

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M.Gregg
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Old 3rd July 2010, 03:32 PM   #14
M Gregg is offline M Gregg  United Kingdom
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Hi,

From a design point of view I would think 10-20 watts would be needed!
So its either Parrallel SET or PP. I still like the KT66 idea though.


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M. Gregg
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Old 3rd July 2010, 05:01 PM   #15
Yvesm is offline Yvesm  France
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Well well ... search this forum for "Baby Huey"

And if you want to wind, here is how I did the OPT for the original 6GW8 version.

http://www.dissident-audio.com/AutoI...le=DA17-2a.pdf

Have fun winding and be patient and carefull.

Yves.
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Old 3rd July 2010, 07:21 PM   #16
M Gregg is offline M Gregg  United Kingdom
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Yvesm,
Regards your transformer diagram. I assume A/B are the speaker terminals. What are X and Y? I assume that the bottom of the winding diagram is the core and you do each layer 5*109T followed by a mylar insulator then 1*32T then the next one on top of the other?
7K anode load output 6Ohms?
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M. Gregg
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Old 4th July 2010, 06:22 AM   #17
Yvesm is offline Yvesm  France
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Hi M. Gregg
You're right !
Apologize for using French and millimeters rather than imperial units: my brain was trained to do so

First and last primary sections have a total of 545 turns, 109 turns per layer (this just fits in the coil former -or bobin) with the specified wire gauge.
Middle one has 1090 turns in 10 layers.
There are no additional insulation between layers.

X and Y terminals have no other use that to allow connecting wires together, nothing else must be connected to.
Note that the thickness of the insulation is different: 0.4mm around the first half secondary and 0.2 mm around the second one
The insulation material is not a mylar foil, but a thing brand named "MylarCelite" wich is a kind of sandwich constitued by a cardboard layer and a Mylar one. It's total thickness is 0.2mm, so you must use 2 turns of it to obtain 0.4mm as noted.
If not available, better use cardboard than plastic which usually have higher dielectric constant.

Be prepared for some deception, irritation and copper vasting before you succeed to neatly roll your first bobin

Yves.

Last edited by Yvesm; 4th July 2010 at 06:25 AM.
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Old 4th July 2010, 08:29 AM   #18
M Gregg is offline M Gregg  United Kingdom
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Yvesm,

However the insulation is critical to prevent HT getting onto the speaker connections under fault conditions! How do you bring out the start and ends of the windings? Could you just sleeve with PTFE and bring them down he edges of the former?
Also I assume 20% UL taps would be 218T from the start of the HT winding on each side.

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M. Gregg
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Old 4th July 2010, 08:40 AM   #19
M Gregg is offline M Gregg  United Kingdom
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Yvesm,

Just another thought! do you varnish each layer as you wind it or just test the finished unit and then dip the winding to seal it?

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M. Gregg
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Old 4th July 2010, 09:14 AM   #20
M Gregg is offline M Gregg  United Kingdom
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Yvesm,

Thank you so much for your help and all members so far!

I suppose the next question is core size and type?

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M. Gregg
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