LL1663 -> 4,6K instead of 5K?

[stigla]

Just a little to think of....

I did some math on this tranny. having a 12+12 : 1 turns ratio gives me a (24*24)*8 = primary Z of 4608 ohms. Thats 392 ohms away from the stated 5000 ohms.

Is this difference for real or is my math way of?

Will this difference of 392 ohms be noticable for the tubes or ears or anything? Dont know if it's a large or a small difference...

in PP class A this will give a load for each tube of 4608 / 2 = 2304 ohms...

If this is not a large difference, then whats the point in having 3,2K trannys or 3,5K or 6,6K or 4,8k and so on...?

anyone?

thnx

stigla

 

[Brett]

Just a little to think of....

I did some math on this tranny. having a 12+12 : 1 turns ratio gives me a (24*24)*8 = primary Z of 4608 ohms. Thats 392 ohms away from the stated 5000 ohms.

Is this difference for real or is my math way of?

Your maths is OK. But all you have done is calculate the theoretical Z from the turns ratio, not what the actual impedance in use is.

Will this difference of 392 ohms be noticable for the tubes or ears or anything? Dont know if it's a large or a small difference...

Not important. Add the two 102 ohm winding resistances an you now have 4812 ohms.

Is the impedance curve for your speaker the same as an 8 ohm resistor?

in PP class A this will give a load for each tube of 4608 / 2 = 2304 ohms...

No.
5000/4 = 1250 ohms

If this is not a large difference, then whats the point in having 3,2K trannys or 3,5K or 6,6K or 4,8k and so on...?

Because different manufacturers specify them in slightly different ways for different reasons. It's not something worth getting hung up about. The quality of the transformer, including the high frequency balance between the two primary windings, and it's inductance are far more important.

More interesting reading on the subject. Article uses a 211SE as an example, but it will generally apply to PP too.
http://www.siteswithstyle.com/VoltSecond/211_Load_lines/211_LOAD_LINE.html

Also, Norman Crowhurst's Amplifier Design series, spefically parts 4a and 4b.
http://www.audioxpress.com/resource/audioclass/index.htm

Steve Bench's explanation of composite loads for PP
http://members.aol.com/sbench102/composit.html