Tony's latest traffo DIY build

[Tony]

good job rolandong......congratulations....

[wakwakni]

hi tony, i have a toroid transformer taken from an old AVR rated at 1kw and I will use for transformer amp. the primary was broken so i need to wind a new one. i just want to know the number of turns on the primary at 220v and and 45v for secondary (or turns per volt). transformer sizes are 5 inch outer diameter and 3 inch inner diameter 2 inch wide.

thanks

[AndrewT]

A core size of 1" by 2" cannot be a 1kVA transformer.
Assuming a flux of 1T you get ~120VA, at 1.5T ~180VA.
Maybe you could run it @ 1.8T and get at the most 225VA.

Tony,
could you check my numbers?

[wakwakni]

hi this is the AVR,

[donnyab]

Tony,

A couple of queries.

I am trying to write a small program [command line type in C] to set out windings for output transformers based largely on Pat Turner's site.

I am a bit confused about the difference between quiescent voltage and the maximum anode voltage on the tube [and quiescent/maximum current].

Pat Turner on his Push-Pull output transformer calculations Page 1 - Class AB1 loadlines -Figure 2 shows a *Q* current at the 500 volt mark. So his quiescent voltage and anode voltage are pretty much the same.
[Also Merlin Blencowe on his website under SE Output Stage also states and highlights the fact that quiescent and anode voltage are the same based on the fact that reactive as opposed to resistive loads are being used ...].

On the other hand Steve Bench on his website under *Loadlines, Power Output and Distortion - Part 5 - Establishing a loadline* is not taking quiescent as maximum anode voltage at all and has a much more sensible way it seems of establishing loadlines .. although he is actually trying to generate composite loadlines which would be next to impossible to program [for me anyway] or at the least very time consuming.

Any thoughts ? My program need to ask this stuff at the beginning for it to work ie calculate the initial Class A, AB, B loadline values.

Next query relates to transformers and Formulas!
Ok Pat Turner works in mms and many text books are US and still use inches and furlongs.

Pat Turner uses a formula as the basis for calculating the area of the transformer centre leg as A = 300*square root(P), which would be in square mms. [Pat Turner OPT calcs Page 2 - Item 14]

RHD4 page 235 gives a formula as A = (square root(P)) / 5.58
A is square inches.

I have another book from 79 called *Practical Transformer Design Handbook* by Lowden which uses the formula as A = 0.16 * square root(P) again in square inches which sort of tallies with the one above, maybe slightly different B values were used.

As I am using Pat Turner's stuff generally I can't see where his formula comes from as there are 645 square mms in a square inch. Do you use pat Turner's site to make your trannies ?

I would prefer to use the original formulas rather than rough formulas for calculating areas etc. such as :

P = 0.707 * J * f * W * A * B

-> but again there is more confusion here as some formulas lump in a figure of 10^-8 such as the Lowden book on Page 58:

P = 0.707 * J * f * W * A * B * 10^-8 !!!!!! [this time in square cms]

What is that ten to the power of minus eight figure as it does not account for different dimensions between mms, cms, inches, it is way too large.
I cannot find an explanation for it ANYWHERE.

Any ideas, I would like to try to reconcile a proper formula to a rough one and go from there ? Thanks

[donnyab]

The figure for Power on Wiki does not include that 10^-8 figure which is weird but it does include it in other calculations ... Wiki/Transformer Design/Equations page

[donnyab]

* WikiBooks/Electronics/Transformer Design/Equations

[Tony]

donnyab,

RDH4 uses imperial units, Patrick uses cgs....

RHD4 page 235 gives a formula as A = (square root(P)) / 5.58
A is square inches.

this is for a power traffo running 50/60 hz, for audio opt i simply scale to 20hz....but i think Patrick's computation is better...one thing i noticed is that if you follow his computations to the letter, you will end up with bigger traffos than commercial offerings....

Pat Turner on his Push-Pull output transformer calculations Page 1 - Class AB1 loadlines -Figure 2 shows a *Q* current at the 500 volt mark. So his quiescent voltage and anode voltage are pretty much the same.
[Also Merlin Blencowe on his website under SE Output Stage also states and highlights the fact that quiescent and anode voltage are the same based on the fact that reactive as opposed to resistive loads are being used ...].

this is because dc resistance was assumed to be zero and it can be done...computations for tubes need not be too accurate...."in the ballpark" is acceptable....

have you seen the book by Wolpert? it is available for download at YvesM's website...

you will soon find out that formulas are fine, but actually building one and testing is even more rewarding...

i just use a wire table, a pencil and paper and then i'm go......

[Tony]

Originally Posted by wakwakni

hi tony, i have a toroid transformer taken from an old AVR rated at 1kw and I will use for transformer amp. the primary was broken so i need to wind a new one. i just want to know the number of turns on the primary at 220v and and 45v for secondary (or turns per volt). transformer sizes are 5 inch outer diameter and 3 inch inner diameter 2 inch wide.

thanks

as you have the traffo with you, why not unwind the wires and count them as you go....

you are asking too much from that torroid....you need to give me the size of the core without the wires, once you have taken out the wires, measure it again and we'll see...

[donnyab]

building one and testing one ... if I ever get that far ha ha

still trying to get my head around all the formulas .. Pat Turner I think uses a very low B figure and that would mean his transformers are much bigger, almost like he is designing them for mild steel ?
so the 300 figure in his formula is probably too big by a factor of up to three

thanks