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21st December 2010, 04:58 PM  #11 
diyAudio Member
Join Date: Dec 2009
Location: Orange County, California.

Thank you for the in depth info on OPT permeability. I do know it is the nature of the beast and adversely effects performance. It will take me a while to understand the exact effect it has on power output and performance.
When dealing with typical off the shelf DIY opt's we tend to rely on reviews of others and what ever testing we are capable of. It would be useful for comparison if the common (Hammond, Edcor, James, Etc) OPT manufactures would provide this info. However your info may help clear up one confusing issue I have when studding the designs of others. Is the permeability effects why some designs use 15 Watt OPTs when their power tube is only capable of about 5 watts? I do understand that bigger is better, to a point. Thanks Again for all your great input. T 
21st December 2010, 05:35 PM  #12  
Account disabled at member's request
Join Date: Apr 2009

Quote:
About every OPT will show core saturation at some low frequency, important is where that point is. So 10W at 20Hz says a lot more. 

21st December 2010, 06:52 PM  #13 
diyAudio Member
Join Date: Jul 2004
Location: Ardeche

Roughly, 8 watts @ 25 Hz produces the same induction that 32 watts @ 50 Hz.(Note the "squared" ratio)
Two different specifications for the same OPT ! 
21st December 2010, 11:06 PM  #14 
diyAudio Member

Here are the basic formulas for manipulating and analyzing transformer core performance characteristics. Use the data from the perm chart where applicable.
1.) input voltage X 10 to the fifth /4.44 X core area of flux tube X frequency X primary turns X stacking factor (usually 92% for E/I core) will provide you with the flux density in kilolines per square inch for an AC rms input. 2.) 3.49 X input voltage X 10 to the sixth/ frequency X core area of flux tube X stacking factor (usually 92% for E/I core) X primary turns will provide you with the flux density in kilogauss per square centimeter for an AC rms input. Multiply 1.) by 0.155 to obtain flux in kilogauss. 1.) and 2.) will provide slightly different values, ignore this. 3.) 0.6 X total primary turns X DC current flowing in the primary / total gap thickness (all of the gaps added together for one magnetic path) will provide you with the flux density for a DC current flowing in the primary of a gaped SE OPT. 4.) 3.2 X primary turns squared (full primary) X core area of flux tube X permeability / core magnetic path length X 10 to the 8th will provide the ac rms permeability of the transformer in question. For gaped core you replace the permeability with the following complex addition. 1/permeability + total gap thickness (all of the gaps added together for one magnetic path) / magnetic path length. You can obtain the magnetic path length from the Thomas and Skinner lamination catalog found here Thomas and Skinner  Transformer Laminations Obviously there are other derivations for the above formulas. If you use the inductance found at minimum excitation and manipulate the third formula, you can arrive at a pretty close approximation of the primary turns used in the coil. This will allow you to take a look at the flux density for SE OPT's and PP OPT's or power transformers. The reason people use larger transformers than what is specified is that they do not have access to the above formulas and perm charts. They got badly burned once or like belts and suspenders and in either case the information needed was just not available, so they figured X three ought to just about do it. Size does matter and to a point bigger is actually better, for some designers work. Not so for others. Bud
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"You and I and every other thing are a dependent arising, empty of any inherent reality" Tsong Ko Pa Last edited by BudP; 21st December 2010 at 11:09 PM. 
22nd December 2010, 04:43 AM  #15 
diyAudio Member
Join Date: Dec 2009
Location: Orange County, California.

Thanks Bud,
I'll need to study this for a while. Tom 
22nd December 2010, 04:52 AM  #16  
diyAudio Member

Quote:
4.) 3.2 X primary turns squared (full primary) X core area of flux tube X 92% stacking factor X permeability / core magnetic path length X 10 to the 8th will provide the ac rms inductance of the transformer in question. Bud
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"You and I and every other thing are a dependent arising, empty of any inherent reality" Tsong Ko Pa 

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