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Old 9th April 2013, 08:45 AM   #451
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... so say you want to wind an audio transformer and work out your number of turns initially and then decide afterwards you also want to provide some negative feedback say 10%.. so you would add in an extra 10% winding in the middle which will not affect the prim and sec voltages as originally calculated .. and will reduce the frequency response per the equations etc ?
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Old 9th April 2013, 08:47 AM   #452
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... or will it affect the secondary impedances and voltages ?
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Old 9th April 2013, 11:02 PM   #453
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Quote:
Originally Posted by donnyab View Post
... so say you want to wind an audio transformer and work out your number of turns initially and then decide afterwards you also want to provide some negative feedback say 10%.. so you would add in an extra 10% winding in the middle which will not affect the prim and sec voltages as originally calculated .. and will reduce the frequency response per the equations etc ?
the 10% extra winding is added to the total primary winding, assuming cathode feedback, frequency response is hardly affected if at all.....
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Old 10th April 2013, 12:50 AM   #454
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Quote:
Originally Posted by donnyab View Post
... or will it affect the secondary impedances and voltages ?
The secondary impedance is given by the load, not the transformer.
The transformer only reflects this load into the primary. For example a ideal stepdown transformer with a winding ratio of 10:1 and terminated into a 8 ohm secundary load would transform this into 800ohm on the primary.
Adding 10% cathode fb-winding would change the winding ratio into 11:1.
With the same 8 ohm load the reflected primary impedanc would now become 11x11x8=968 ohm. The secondary voltage will drop. By how much depends not only on the winding ratio but also on the source impedance. Triodes will work happily into a 21% higher load. Pentodes can be a bit more grumpy. Make sure the additional winding is spread out over the full windingwidth.

Last edited by gorgon53; 10th April 2013 at 12:58 AM.
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Old 10th April 2013, 04:33 AM   #455
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yes, impedance ratios are in fact just turns ratio, it is what load you connect to the secondary that determines what impedance is reflected to the primary windings.....

Wolpert gives a very good tip, make the winding widths the same for all primary and secondary windings....
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Old 28th April 2013, 10:17 AM   #456
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tony,

I know you are not a world renowned expert on this stuff but you are one of the few [only ?] individuals here that actually winds things and provides photos so any suggestions are helpful .. so another few quick queries on our favourite subject.

I have most of the parts now to get a winder built hopefully next week but I am still trying to finish my first complete draft of this program and I remain confused about cathode feedback.

Say I was not using CF I would design as normal .. each trafo end terminal to plate and centre tap to B+.
So I have arrived at a design with 20 primary layers, a transformer designed for particular valves with a particular primary plate to plate impedance and therefore specific secondary impedances. Pat Turner shows this info using small tables on his site....which someday I hope to replicate!.

OK I change my mind and I decide to use CF instead, say 10% CF.

Now the big question is should I ADD two more windings to the design - and that would then affect my secondary impedances .. so they would need recalculation ?

OR would it be better to designate two of the existing windings to CF ?
If I designated two of these my secondary impedance table would then not need to be recalculated, is that right ?

I am also wondering if it matters where I would place the extra winding in the transformer OR if I used two of the existing layers, which two of the 20 I should use.
The reason I ask this is because I want the program to spit out the winding diagrams and I need to resolve these things in my own head before I program it, the visual bits of this [such as they are] will be time consuming for me to do as a non-programmer!!

Pat Turner on his output-trans-PP-calc-3 pages - Fig 23 - shows a plan with four secondaries and a CF winding, but if I had a trafo with an ODD number of secondaries would it matter exactly where I place the CF winding .

In other words should I use the two windings on either side of the central secondary or even a bit further out or does it even really matter that much exactly where I place the feedback windings ?
Again I know you are not a professional builder but if you have used CF in your designs you may be able to shed some light. I will probably only find this out properly when I wind one - and attempt to measure values.

I have a shed load more queries on practical things but this post would be way too long, I will leave them until I actually build the winder.
I will send you a copy of the program when I finish it if you want to give it a spin.
It is probably about twenty pages long so far and counting ...about 60% done.
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Old 28th April 2013, 10:36 AM   #457
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way i understood it, any winding that does not connect to the speakers are primary windings it does not matter if it is connected to plate or to cathode.....

therefore, the turns ratio is for total primary windings to all secondary windings....

i think Pat Turner gave out all the information in his website, just use them....

i use the traditional pencil and paper technic in making my traffos....

there is a book by Wolpert available for download at YvesM's website...that book will give you an easier to follow design examples...how to make audio output transformer
post#6 even gives you a software to calculate/design an output transformer...
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Old 28th April 2013, 11:05 AM   #458
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I have installed Yves and it is good but what I am aiming for is something that will do everything - apart from actually wind it.

I want to show the winding arrangements on screen including insulation, primaries and secondaries, also how the secondaries are divided up and organised...in series or parallel.

Type in valve parameters, voltages, number of pairs of valves and RUN, then wind the transformer basically by looking at the screen .. if you will.
Basically you could leave your pencil and paper in the drawer and never have to use them again.
Partly this is also a programming exercise for me - I am also intent on doing a program for the McLyman book *Transformer and Inductor Design* for switchmode stuff as well if I can get around to it.
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Old 29th April 2013, 09:31 PM   #459
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tony, out of interest as someone who has been winding transformers for a while how long does it take you to do full calcs by hand from start to finish ?
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Old 29th April 2013, 10:02 PM   #460
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Quote:
Originally Posted by donnyab View Post
tony, out of interest as someone who has been winding transformers for a while how long does it take you to do full calcs by hand from start to finish ?
no more than a few minutes, the actual hard work is in the actual building, planning, gathering the parts, etc......i am a practical guy, i know what i should be concerned with and what matters the most, if you think of everything you may never get started at all....

oh. another thing going for me, i know at least three old-timers in the business of rewinding tube OPT's, they give me lot's of tips, plus i get to see how they actually do their thing.... and then i get to dismantle opts from discarded tv sets, amps etc....
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