another HV tidbit

from http://plop.phys.cwru.edu/repairfaq/REPAIR/F_gadget.html#GADGET_014

14. Why the yoke is needed to keep the horizontal deflection
system happy

If you unplug the yoke (even if there is no interlock), while the system may
still work to some extent but performance will be poor. High voltage will be
reduced and parts may overheat (and possibly blow up).

(From: Jeroen Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

Of course that doesn't work. The flyback capacitor is tuned for the presence
of both inductances: line transformer and deflection coil. If you remove the
deflection coil then the remaining primary transformer inductance is about 5
times as large. So, rule-of-thumb, you would have to decrease the flyback
capacitor by a factor of approximate 5. But that's not all:

Without the deflection coil, a lot less current runs through the horizontal
output transistor. So, in all likelihood, it will now be overdriven. So you
need to reduce the base drive. But that's not all:

If you remove the picture tube capacitance and the deflection coil then all
peak energy demand must be delivered from the primary winding of the line
transformer. Even the shortest peak load will cause saturation. The parallel
deflection coil will at least lend some temporary energy, and the picture tube
capacitance does an even better job. A good high-voltage source without the
benefit of a deflection coil is more expensive...

If you *must* get rid of the 'ugly' deflection coil, then you may want to
replace it with an equivalent 'pretty' coil. But:

* It must be able to carry the peak current without saturation (a deflection
  coil has such a huge air gap that it can not possibly ever saturate, but a
  smaller coil can).

* It must have a low enough dissipation so you might have to wind it with
  litz-like wire (multi-stranded isolated), do not underestimate the losses in
  high-frequency coils, mostly due to skin- and proximity-effect.

* Yes, it can be done, good luck.

And you might want to add a discrete high-voltage capacitor. How to isolate
the wiring (corona discharge!) is left as an exercise to the reader... (We
pot them in convenient blocks).
Received on Tue Jul 20 19:04:03 1999