Chris,
The best way is by using an RF current transformer connected to a storage
scope.
This is to look at the primary tank currents. Many folks have done this.
Terry F.
probably has some stuff written up about it. Some folks have also used
an
antenna at a distance from the coil to pick up the RF and look at it on
the
scope, but sometimes it's hard to get a clean signal of the primary.
Instead
the secondary and primary signal may be seen overlapped which makes the
display look confused on the scope. Using a sync rotary, the waveform
can
be seen without a storage scope. Using async gaps, it's hard to see
anything
clearly without a storage scope because the signal can't be synch'ed
easily.
The modern digital scopes can easily deal with these signals and issue.
John