Re: [TCML] Re: current limit system and X-rays

[Frank <fxrays@xxxxxxxxxx>]

The picture helps a little bit, thanks.

Modern X ray machines use Tesla coils to generate the high 
voltage  and rectify it for the necessary DC to run the Coolidge 
type, filament heated, tubes. This significantly reduces weight and 
cost of the X ray power supply. Took 100 yrs for mfgrs to come back 
to this type of supply!

Interesting to note that Tesla coils were used to power X ray tubes 
in 1897 and fell out of favor due to the shortened life of the tube.
They developed a special high frequency X ray tube to run off of 
Tesla currents, essentially an  2-in-one tube with a rectifying 
section built in but the ideas were short lived as the Coolidge tube 
came out and killed the use of the gas type X ray tube in the 1915's.

Modern Coolidge tubes have a vacuum as high as possible  and is 
basically an insulator in the electrical sense. They require a heated 
filament to produce an electron stream.
Think about the modern tube, the anode and cathode may be 1/4 to 1" 
apart and the tubes are hit with up to 200KV. Has to be a good 
insulator or there would be internal arcing across the elements.

You can make an unfocused X ray tube using an old radio tube and 
exciting it with  high frequency HV.

Cold cathode X ray tubes have a small amount of gas in them so they 
will conduct when HV is applied and the tubes increase in vacuum with 
use to the point they will not longer conduct. Hence, tubes were 
fitted with regulators to inject small amounts of gas to lower the 
vacuum to make the tube operational within the desired limits.

Tesla had a single electrode X ray tube, it worked but was un 
focused. I have a working replica of one.
I have a modern NDT X ray that uses a HF HV supply and a Lenard's 
tube! Talk about using 100 yr old ideas with modern parts and it is 
even battery operated!
I have a large collection of X ray tubes from 1896 to the 1930's.

If you want to generate any X rays or are worried about them, the 
vacuum level must be high enough in a gas, Geissler or Crookes tube 
before X rays will be produced. Basically a gas tube must "back up" 
or when connected in parallel with a spark gap and the gap opened, 
the tube starts conduction at a certain gap distance, 2" of spark.

Basic Geissler and Crookes tubes will back up 1/8 to 1/2" of spark 
typically and start conducting long before the voltage is high enough 
to allow X rays to be produced.

Remember, these gas tubes turn into voltage regulators once they 
conduct they will try and maintain that voltage drop and just 
continue to draw current as the voltage increases.

Now, using a single ended high frequency connection as you indicated 
in your link, the tube will conduct and not draw excess current, 
however, X rays will not be produced if the pressure level of the 
tube is not correct. See above.

Using a modern Coolidge type X ray tube will do nothing as its vacuum 
level is too high and the tube is just an insulator.

Contact me off line if you want more info or pix of some of the tubes.

Thanks! Frank

At 07:56 AM 9/28/2010, you wrote:
> well. i think no one understands my words.
> here it is :
> My Drawing <http://imgur.com/v2njI.png>
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> Tesla mailing list
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> http://www.pupman.com/mailman/listinfo/tesla
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