[Amps] Re: Step-start calculation

[Dennis12Amplify at aol.com]

In a message dated 11/21/04 1:11:18 PM Central Standard Time, 
wa1hco at adelphia.net writes:
Dennis...

A transformer has inductance when open circuit, but when something's 
connected to its secondary, that impedance get transferred to the 
primary by the square of the turns ratio. So, when the transformer runs 
open circuit, a nearly infinite impedance gets transferred to the 
primary and it draw little current. When a transformer has a a load such 
as a resistor or discharged capacitor, then the primary impedance 
depends on the winding resistances, turns ratio and coupling coeficient. 
For most transformers one can model the coupling as perfect.

jeff, wa1hco
***Jeff,

 ***Thanks for the education.

 ***I still find it very hard to believe that there can be an almost 
instantaneous change in the secondary current when the secondary inductance is 
probably measured in multiples of HENRYS, and I know it's been a long time since I 
worked in that area, but when I did, I rarely saw 'M' values greater than .85 
for a high voltage step up transformer.
 The turns ratio is a big part of the problem in this case, because the ratio 
is so high, it is very hard to get a coefficient of coupling much higher than 
that. Maybe the technology has changed and that is no longer the case.

 ***Now if that same transformer was bifilar wound with a 1 to 1 or even a 4 
to 1 ratio I would understand completely and absolutely agree with you.

 ***If what you are saying is true, then wouldn't the reciprocal also be true 
and allow me to greatly extend the frequency range of my tube stereo output 
transformer by making my speaker load impedance as low as possible; like 
paralleling ten 4 ohm speakers for an output load of only .4 ohms on the secondary 
of the output transformer? 
 I understand that the efficiency would be poor unless the turns ratio was 
readjusted, but the audio bandwidth should be HUGE!

 ***I guess the best way to test this concept would be to run a 
'significant', (like 1 ampere for a high power linear amplifier transformer), amount of DC 
current through the secondary winding, then short the primary and open the 
secondary circuit. If what you say is true, there should be no high voltage spike 
when the secondary discharges because of the shorted primary and the perfect 
coupling. I, personally, would not want to be holding both ends of those 
secondary leads while they were being open circuited......

***Regards,

***Dennis W. Ostrowski