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Odd/Crazy output transformer design?
Odd/Crazy output transformer design?
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Old 16th July 2010, 07:17 PM   #11
Ty_Bower is offline Ty_Bower  United States
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I enjoyed reading the Lenard Audio page, but found a horrible glaring error on page 4:

Cathode bias is described as Class A. Using 2 output valves is described as push pull. Therefore 2 output valves that are Cathode biased is described as Class A push pull.
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Old 16th July 2010, 11:19 PM   #12
Sch3mat1c is offline Sch3mat1c  United States
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That's a faulty definition of class A. It is a function description of cathode biasing.

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Old 17th July 2010, 02:26 AM   #13
Richard Ellis is offline Richard Ellis  Argentina
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Default Experimental TX

I always thought EI, Toroids, Cs'...et. al. ....were oriented too much to mass production, with little thought toward optimal performance.
Taking into consideration the three dimensional shape of the magnetic fields generated, one could come up with a superior design of laminations.
Myself, I thought, a roughly apple shaped arrangement of concentric laminations would work optimally.
I do believe when someone out there stumbles upon a core shape/composition...winding of bizarre conductor/insulator materials the EI will go the way of the Horse & Buggy.

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Old 17th July 2010, 02:35 AM   #14
Richard Ellis is offline Richard Ellis  Argentina
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Like this here.

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Old 17th July 2010, 04:51 AM   #15
TheGimp is offline TheGimp  United States
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Cost vs performance.

Damn bean counters always win.

Look at E core/ I core lamination's and they are "Loss-Less". You get two Es and two I's from one rectangular section. Allign it properly and you minimize material loss and maximize profit.

So spins the world.

Last edited by TheGimp; 17th July 2010 at 04:56 AM.
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Old 17th July 2010, 02:01 PM   #16
jlsem is offline jlsem  United States
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Originally Posted by Matt.B.H. View Post
Sorry guys been working away again

This seems to be going the way of toroids which was not my intention, merely a reply to Smoking Amp.

Yes torroids work but that was not the point of my OP.

I agree that each layer would need to be stuck together to stop any audible ringing. The HV qualitys of flexible PCB are such that 1 though (your mill) will withstand 3KV.

Cheers Matt.
I'm not sure that sticking the "windings" together is that critical; any ringing or vibration in an OPT would be due to magnetostriction in the core. I'm fascinated by your idea. What kind of fill density have you been able to calculate? At first glance using a sort of "edgewound" coil appears to have some advantages in terms of coupling.

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Old 12th December 2010, 05:45 AM   #17
Matt BH is offline Matt BH  United Kingdom
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The apple shape does indeed look ideal. I have heard/read that some input trannys were made by Tellefunken this way. Any German readers to confirm?

I am under way now winding some transformers using the Pi arrangement. I have worked a way to make it fairly easy using normal methods, if extremely labour intsensive.

I did think to start that the multi-layer PCB approach would be easy. It is not. I have found a way over the inter-conection problems but it is by no means trivial.

Using normal winding methods, Crowhurst hints at some handy tricks. If the bobbin consisted of a load of sections Ie sectioned vertically a fair few times. Then each section could be wound in segments and the start of each winding reversed. Pretty hard to explain. The paper is called Output transformer Design.

I plan to make this pair of trannys and compare them to a pair using the same core cross section and of fairly standard construction. The only reasoning behind this is because I would like to see if there really is an advantage and if it is worth me persuing the PCB design as this is extremely expensive as a prototype.

Anyway, can anyone point me to a good high voltage, low output impedence amplifier design? I remember Elektor doing one a while back.

Cheers Matt.
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Old 12th December 2010, 06:31 AM   #18
Terry Demol is offline Terry Demol  Australia
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Originally Posted by Matt.B.H. View Post
I have seen these trannys wound by John Lenard Burnett:

Lenard Audio - Education - Valve Amps

Scroll down to the Pi wound ones.

I have had an idea based on the already existing planar transformers used in switch mode supplies but using pair of iron c-cores.

If I had a load of flexible PCBs made with the windings on either side connected with vias and insulated either side then stacked up P-S-P-S etc. Then connected to form the whole winding for P and S.

This should make a very high bandwidth tranny with almost ideal coupling that could be configured for all sorts eg. UL, CFB etc. The insulation of flexible pcbs is capable of 3KV continuous so no probs with insulation. interlayer capacitance could be problem though. Thicker insulation?

What do you guys think? Is it feasable? I know it would be expensive for one or two but for lots it would be minimal. The transformers could be considered identical due to the high tolerance of production and the balance for a push pull tranny would be perfect.

A bit like this:


Cheers Matt.
That's a blast from the past.

I believe the first Pi OP trannies for Lenard Audio were wound by Alkay
Transformers - I was working there when we did them.

They were pretty difficult to wind. Every one of those sections was, from
memory, done separately and then they were stacked together with nomex
insulation between them.

The whole idea of Pi winding is to reduce the layer to layer voltage gradient
and distributed capacitance. With this style of winding there is much lower
paralleled winding capacitance so end result is greater bandwidth -

The amps were, fom memory open loop KT88 push pull.


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Old 12th December 2010, 10:36 AM   #19
tinitus is offline tinitus  Europe
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Odd/Crazy output transformer design?
aha, fully balanced PP OPT, thats what it is then

the two CT goes together
either directly at OPT, or at supply
and each An to each tube anode/plate

any suggestions how I should wire the secondary
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Old 12th December 2010, 05:18 PM   #20
smoking-amp is offline smoking-amp  United States
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Looking at Richard's "apple" shaped xfmr above (a standard ferrite pot core essentially), I am reminded of a discussion on DIY recently where this setup was inverted to become an inverted toroid xfmr with wire forming the toroid "core" and lamination strip or steel wire forming the "winding" on the outside. Very easy to wind the copper at least. Would use a very large diameter bobbin of small cross section ( a small wire winding window), maybe 8 or 10 inch major diameter.

This could be modified to a stack of large diameter/ thin cross section Pi wound coils (say primary 1, sec., pri 2) Then the magnetic material gets wound over the bobbin set to maybe a 1/4 inch depth using a toroid winder. A conventional toroid winder would work for steel wire at least. These winders also have a special shuttle for winding insulating (thin mylar etc) tape on a toroid, but unfortunately they sharply bend the tape during its removal from the shuttle. This would have to be re-worked for steel tape. Magnetic tape would have the advantage of grain orientation available, never heard of grain oriented wire though. Could even use permalloy tape, readily available.

As any transformer winder knows, the balance between copper and steel can be tipped either way. With copper so expensive lately, tipping to more iron makes good economic sense, and less turns of copper means less winding resistance. Looking at the inducatance formula, the lower turns has to be offset by larger core area AND lower magnetic path length. This is exactly the forte of this method. (if you work out all the formulas, you will find that the two methods (this versus traditional) can give equivalent results for equivalent materials) Reducing the usual 2000 to 3000 turn primary wind down to 100s of turns certainly has to be attractive for DIY also. Although the toroid winder machine will still have to wind 1000s of "turns" of steel wire or tape. A bobbin with a round cross section bottom and a rounded wire pile-up on top could optimize the magnetic path length further.

Should probably check with Kenpeter to see if he has wound one of these already on a plastic bicycle rim "bobbin" (copper magnet wire in the rim) with enamel insulated steel bailing wire wound over the outside.

Last edited by smoking-amp; 12th December 2010 at 05:34 PM.
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