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magnifier vs. classic tc (magnifier modeling)




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From:  FutureT [SMTP:FutureT-at-aol-dot-com]
Sent:  Tuesday, March 17, 1998 9:25 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: magnifier vs. classic tc (magnifier modeling)

Antonio, all,

New tests:

I wound a new secondary in order to test the magnifier at k = .51, (for
the driver).  This new secondary is 6 1/2" dia x 3.3" high, 94 turns of
#24 pvc wire (1.5mH). The same 3" x 12" extra coil was used.  Scope
observation of the ~ 11uS RF beat period showed the effective coupling
to be about k = .18, which happens to be the same coupling that I used
in the original classic TC test in the previous posting.  Both the maggy
and the classic coil (which had the same effective k ) performed 
similarly as shown in the table below.

    Classic TC                                Magnifier
    ----------------                                --------------
       k = .18                                      k = .51
                                          effective  k = .18
  beat period ~ 11uS          beat period ~  11uS
   quench -- poor                   quench -- poor
       (3rd -- 4th notch)               (3rd -- 4th notch)
 spark,  3 1/2"  max               spark,  3 1/2"  max

Next, a secondary with a higher inductance of 5mH (but of the 
same physical dimensions as the 1.5mH sec), was installed, to
verify that the effective coupling would increase as the secondary and 
extra coil inductances became more similar.  Tests were done using
the 13mH extra coil, and also using a 20mH extra coil.

    Driver k            Effective k (meas)    (calc)     Lr/Ls      Quench
                                   (extra coil)

  .51  (1.5mH)           .18  (13mH)           .16      8.7:1    4th notch    

  .45  (5mH)              .22  (20mH)           .20       4:1     5th notch

  .42  (5mH)              .29   (13mH)            .22      2.8:1    6th notch
 
It can be seen in the table above that as the ratio of
inductance between driver and extra coil decreases, the driver k
and the effective k become more similar.  Some of the differences
between the calc and measured k values may be explained by
losses in the system, however the last entry seems anomalous.
More work is needed.  Effective k values were measured by 
observation of the beat period relative to Fo. 

The series quenching rotary sync gap was used in these tests, and
it had the same degree of difficulty in quenching in both the classic coil
and in the magnifier.  I.e. quenching difficulty depended only on the 
effective k value, not on the driver k.

Conclusions:  Even in these tightly coupled magnifier designs,
the effective coupling as measured by RF beat durations, was
much looser than the driver k, and often similar to typical 
classic coil k values.  Spark gap quenching demands for the same 
effective k value, were the same in both the magnifier and in the
classic TC.  Overall performance was similar, maggy vs. classic TC.

Thanks Antonio for the calculations and comments regarding my
prior posting.

Comments welcomed.

John Freau