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Old 4th July 2010, 09:55 AM   #21
rjb is offline rjb  New Zealand
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I suggest you accept any help from BudP that you can get.
In a Philips Tech Library book by E.Rodenhuis "HiFi Amplifier Circuits", a detailed instruction for winding a PP UL transformer for a 20w EL84 amp is given To get very good performance it has 10 primary and 8 secondary coils to provide matching to 8 and 16 ohms. Central core is 50mm x 25mm.
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Old 4th July 2010, 10:37 AM   #22
M Gregg is offline M Gregg  United Kingdom
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Hi rjb,

I hope that "those that know" are watching and will point us in the correct direction should we stray! I know this is a big learning curve and is not meant to be a closed discussion. Hopefully we will get to a point where we have a small pp trasformer as a first attempt with good performance. If this works then we can try and get more advanced.
Just a thought "an engineer can build an engine with a drawing not having to do the design if the parts are available". For valve lovers this would also be true with a drawing an some engineering knowledge.
I was hoping BudP would comment!

Regards
M. Gregg
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Old 4th July 2010, 11:05 AM   #23
Yvesm is offline Yvesm  France
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Quote:
Originally Posted by M Gregg View Post
. . .
Also I assume 20% UL taps would be 218T from the start of the HT winding on each side.
No, this design can't be converted in an UL one simply by adding taps.
You must use completley different winding organisation to maintain symmetric coupling between anodes, screens and LSP windings.

Core size and type is indicated at the bottom : 22mm by 34mm thongue, M6X laminations.

Yves.
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Old 4th July 2010, 01:37 PM   #24
M Gregg is offline M Gregg  United Kingdom
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Yvesm,

Do you still use this transformer now?
Have you tried triode connected as well as pentode?

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M. Gregg
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Old 4th July 2010, 02:51 PM   #25
Yvesm is offline Yvesm  France
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Yes, it's still my dayly amp !
See the original schemo here:
Push Pull ECL86/6GW8
Local feed back around the output stage was used to reach the lo Rp of triodes while keeping the efficiency of pentodes.

You will see that the OPT design was slightly modified (use of Mylar Celite instead of Teflon that not proved to be superior but more difficult to get)

A friend of mine also draw a PCB for "lazy" builders . . .
Audiyofan.org • Afficher le sujet - Commande groupée PCB pour Push-Pull ECL86 Dissident Audio

Sorry, loooong french speaking thread but pictures say almost all

As far as I know, about a dozen was built successfully.

Yves.

Last edited by Yvesm; 4th July 2010 at 02:54 PM.
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Old 4th July 2010, 09:16 PM   #26
M Gregg is offline M Gregg  United Kingdom
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Hi,

Yvesm has given us a pentode transformer thank you so much!

Does anyone know how to wind Transformers for EL84 20% UL taps?

Regards
M. Gregg
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Old 4th July 2010, 11:06 PM   #27
rjb is offline rjb  New Zealand
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Hi Gregg
The transformer I mentioned has 40% taps. Apparently 20% gives best distortion figures, very similar to triode operation, , but 40% is better if higher power outputs are required. If you send me an email I can scan the whole article for you.
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Old 5th July 2010, 04:36 PM   #28
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Lightbulb BA-TrafoWiz

I can calc windings for push-pull (not SE, sorry), EI & Double C Core, M3/M4/M6 CRGO silicon steel (I may add Hi-B and permalloy later, but right now I have no enough data to do so).

Software is based on methodology known as "method of equivalent generators" which I took from the number of academic-level Russian books published in 50th and 60th. I verified data generated by software from book's samples, and it was correct.

Apart from number of turns, my software BA-TrafoWiz provides approximate values for leakage inductance, low-frequency roll-off (at max/low power) caused by idle current imbalance, parameters of final coil/windings dimensions (incl. R(dc) of both), and simulation of winding process which allow to check how windings fit coil/bobbin much more precisely then generic formulas. So far I programmed 4x4 layout only.

Also, it estimates worst-case scenario analysis of THD/IM, but it seems to be based on very old data and low-quality iron, so results are overestimated at 10x degree I believe.

I ordered 2 sample transformers which I designed with this software, they stand on my table, but I had no time to finish tests amp unit yet (as the Russian joke goes "shoemaker left without boots ").

There is a plenty of controversy in various areas of audio transformer design (e.g. A/AB class primary# of turns, including or excluding approx efficiency in secondary winding calculation, etc.). Each author/engineer insists on its own version of truth, so its up to you to accept or decline all that stuff.

I can start new thread for core submission, and upon having free time will post calculations.

Offer is free as freedom of speech
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Old 5th July 2010, 06:07 PM   #29
M Gregg is offline M Gregg  United Kingdom
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Linuksguru,

Thank you for your kind offer. Please place a link to your thread here!

Regards
M. Gregg
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Old 5th July 2010, 07:00 PM   #30
Sheldon is offline Sheldon  United States
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I've got some EI 112, 0.014"(or .356mm) from here:

PRODUCTS

I also have some bobbins for a square stack (which you can split if you need a bigger stack).

You can have for shipping (and maybe a small contribution to DIY, if you are feeling generous).

Enough for a few parties to make a pair of small PP transformers (SE too, if you only need a couple of watts).

Sheldon
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