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Re: Air core chokes?



In a message dated 97-01-12 00:39:44 EST, you write:

<< 
 I'd like to protect my neon with chokes and spark gaps as per the list.
 But, I don't know where to get the toroid cores I've seen mentioned
 on this list.  Is it possible to wind an air-core choke to get some
 protection?  I have a fair amount of #30 and #18 magnet wire at the
 moment.
 
 Also, how do I set the gaps on a protective spark gap?  Just set it
 'till it stops firing, or can I calculate what I need.  (12kv 30ma neon
 and probably about .005 uF main capacitance.)
 
 Lastly, I have seen schematics where there is a .001 uf cap for
 protection too.  Am I correct in assuming that I have to deduct this
 from the .005 uf main cap to avoid overloading the neon?  I guess the
 sparks will suffer but the longevity will be better.
 
 	Steve Falco
 	sfalco-at-worldnet.att-dot-net
  >>
Steve,

I am currently using a 12 kv 30 ma neon with a .005 mfd cap and have my spark
gaps set to about .41" on each side.   At this setting, they fire frequently
but don't stay fired and don't seem to detract from the performance of the
coil.

Regarding capacitors for neon protection:  There has been some discussion on
this.  I used them on my 6.0" coil but am not using them on the new smaller
coil.  You usually place them from the transformer outputs to RF ground.
 They want to be several hundred picofarads and somewhat lossy at RF
frequencies, like mylar caps.  You want low capacitive reactance at the coil
operating frequency but high reactance at line frequency to keep the losses
low.

I am presentlly using 3,000 ohm resistors and 1.0 mh chokes in series with
each high voltage lead from the transformer for protection.  Which seems to
be working fine.  I ordered the choke cores from Marlin P. Jones
(1-800-432-9937).  They are 2.54" O.D. and 1.22" I.D.  I wrapped them with
electrical tape then wound on as much #26 pvc insulated wire as I could get
on with layers of tape between layers of wire.  I understand that you really
want something like 5 to 10 mh minimum - which would mean much larger cores
or much smaller wire.  At the operating frequency of my coil (about 320 khz)
1 mh is equal to about 2,000 ohms of inductive reactance.

Ed Sonderman