This is topic Ignitor question, spark gap in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Marc Jones (Member # 29) on 03-17-2003, 08:26 PM:
What is the purpose, and how would you tell if it is correctly adjusted. One thing I notice with a knisley L2000 lamp house. I had problems one night with igniting a bulb with approx 1000 hrs, While tring to ignite you could see the spark in the spark gap, but no high voltage or sparking across the bulb. Just curious if the spark gap would possibly be problem or out of adjustment.
Posted by Mark Gulbrandsen (Member # 72) on 03-17-2003, 09:02 PM:
Marc,
If you fire it with the room lights off you'll probably see it arcing to the mirror at the rear....This is very common. Try looking at the insulator that goes through the mirror and see if its gotten a bit crispy at all. Things tend to conduct when they turn to carbon. If the inslator is ok you may ahev a bad lamp, or a lamp which has the ignition wire too close to the mirror. Get the lamp manufacturers permission BEFORE you remove the nichrome wire. If you don't find any wire there then thats also another possibility. A lamp with that many hours sometimes needs the wire to help conduct the HV and then ionize the gas.
If the lamphouse fires the ignoitor automatically when you turn it on the rectifier would seem to be ok....BUT the relay pcb in the Irem rectifiers does fail once in a while.
Mark @ CLACO
Posted by Jon Bartow (Member # 241) on 03-17-2003, 10:25 PM:
Marc, the L2000 ignitor has a factory preset spark gap, don't worry about it. Mark is on the right path, I'll bet the plug that goes in the back of the reflector is grounding out the bulb. (very, very common with that lamphouse) Is that plug held in place by a rubber o-ring or a coil spring? You should order a replacement, they are very cheap.
Jonathan
Posted by Marc Jones (Member # 29) on 03-17-2003, 10:38 PM:
The insulator piece thru the reflector has been replace, I had that problem before so all of my knisely lamps have the teflon looking piece. The rectifier is a Kniesly also, So you can rule out the relay board. Just the thing I was thinking of was if the voltage is jumping across the spark gap then I would figure that that was the path of least resistance and my voltage is flowing in that direction. So my thought would be if the spark gap was opened then it would arc across the bulb. If this makes sense. I also verified that I had good connections on both ends of the bulb, so I can rule that out.
Thanks for the responses
Posted by Tim Reed (Member # 137) on 03-18-2003, 12:17 AM:
FWIW, the spark gap doesn't matter, as long as there is a gap. It's a spark gap oscillator in actuality. Changing the gap width (without making it so wide it won't fire, or so close that the ends practically touch) really only changes the fundamental frequency of the tank circuit it is a part of.
Posted by Gordon McLeod (Member # 33) on 03-18-2003, 09:52 AM:
changing the frequency can have other effects. If it get too high the HV will start to tend to fly off more to other items in the lamphouse
If it is too low then the radiated noise into soundsystems can get worse.
Also some of the HV caps don't particularly like too high of frequency
It is normally tuned to about 30KHz according to an old Osram report
Posted by Tim Reed (Member # 137) on 03-18-2003, 10:41 AM:
Didn't know that, Gordon. I figured it probably had some effect, but was probably minute or negligible. I can understand caps having reactivity issues at higher frequencies, but I don't know how much the frequency changes with the gap width, either.
I've made igniters before, using spare parts in an emergency. For the spark gap, I just placed two wires a short distance apart. As long as it oscillated, it fired.
![[Smile]](smile.gif)
Posted by Marc Jones (Member # 29) on 03-18-2003, 11:25 AM:
Thanks now I know, just curious what/where would you get a scope probe to handle the voltage.
Thanks for the info
Posted by Mark Gulbrandsen (Member # 72) on 03-18-2003, 01:01 PM:
If you change the arc gap size it just changes the frequency of the oscillation. They work like an old arc gap transmitter.
Mark @ CLACO
Posted by Tim Reed (Member # 137) on 03-18-2003, 04:00 PM:
Precisely.
Posted by System Notices (Member # 2357) on 04-14-2009, 01:20 AM:
It has been 2218 days since the last post.
Posted by Eric Robinson (Member # 2966) on 04-14-2009, 01:20 AM:
Couldn't someone just use a neon sign transformer to create a spark in the bulb, I have one with a 25K secondary that is able to conduct a good length through air.
Am I missing something?
Posted by Jim Cassedy (Member # 4115) on 04-14-2009, 10:43 PM:
Marc-
I have several Knisley lamphouses and as others have said,
this is not an uncommon problem with them.
As the bulb ages and becomes a bit harder to strike, you'll
find that very often the negative terminal of the bulb is
arcing to the metal frame that supports the mirror right
at the point where the ass-end of the bulb goes through
the hole in the center of the reflector.
The problem is worse in areas with high humidity.
In several of my lamps, I've fabricated a teflon
collar which pokes through the mirror hole and
provides additional insulation. I'm not sure if
the lamps originally had an insulator there or not,
but the lamps I was working with had none.
However, I see that a shipment of 3 new Knisley L2000's
that I just received, but haven't installed yet, come
with an insulating collar similar to the ones I made.