I believe that your K is in the ballpark for the WLW PA. Looking at
the Radiotron designers handbook there is a chart of K versus spacing
for two identical coaxial solenoids. The range is from 0.004 to > 0.1
for receiver circuits. There is also an empirical formula for spiral
flat coils. If it took K to be .143 to get the proper tube plate load
impedance, then that should be the correct k for the WLW
transformer,IMHO.
73
john
>John,
>
>The coefficient of coupling figure I came up with, will reflect the required
>load resistance that the 167 kW amplifier sees, to a load resistance the tube
>plates want to see.
>
>I'm actually more interested in knowing what practical values of k would
>bethat are actually realizable. I don't think, for example, you
>could get a k of 1
>with an air core transformer. In some of my old EE texts that describe
>coupled solenoid coils, k figures or .008. .010 or thereabouts, are given
>
>I found a program on the Internet that allows the modeling of coupled coils
>of all kinds. With the approximate geometry figures I have for the WLW plate
>tank, I got k values around .1, but the problem now is, to what degree of
>coupling does that k represent? It's pretty easy to calculate, but
>not so easy to
>model. I doubt that you would want the coupling much greater than "optimum"
>coupling, which is 1.5 * critical. The value for critical coupling
>is dependent on
>the uncoupled Q of the tuned primary and secondary. The rub there is knowing
>what "loading" resistance the tube would be providing while unloaded.
>
>I think if a k value of .143 is practically realizable for two coupled flat
>spiral coils, I think I will conclude my analysis at this point
>then. One thing
>I did learn from running this coupled coil simulator is, it was much easier
>getting a higher degree of coupling with flat coils compared with two solenoid
>type coil physically separated by the dame distance. So summarize, I'm more
>interested in knowing if a coupling coefficient of .143 is
>physically attainable
>than I am knowing if this K value represents loose, critical or optimum
>coupling.
>
>One might be able to make electrical measurements on the coil that is at the
>site, but that 50,000 watt signal there on 700 kHz might raise heck with such
>an experiment :-D
>
>Jeff Glass, BSEE CSRE
>Northern Illinois University
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