Re: More tube coil stuff (Carl Willis)...

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 9/1/00 8:13:42 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: cwillis-at-guilford.edu 

>  this is also where I get the longest
>  sparks with my sputter arrangement.

Carl,

In my grid-blocking (sputter) mode work, the sparks were always
shorter than in normal CW operation which is why I switched to
the true staccato operation.
>  
>  >>>Are you sure the coil is tuned very precisely?  I would expect at least
>  >>>a 19" discharge using the nail. 
>  
>  I think tube coils are extrememly sensitive to tuning as opposed to
>  disruptive coils. Brushes and streamers are going to have different
>  impedances, and maybe this is reflected by having to retune the coil to get
>  better results with one or the other.

Also, the oscillator may start up differently or run more stable at
certain tune points, but yes, the tuning definitely changes the
spark appearance.

>  >>>I find a fine tuning adjustment range over which the spark length will
>  >>>remain the same, but towards the sides of which will reduce the tube
>  >>>plate redness.
>  
>  My plate does not get red to any extent at all, perhaps because of the
>  low-duty cycle of sputter mode.  It does redden up considerably as grid
>  leak RC is lowered towards CW mode, and when it is CW (I haven't run it
>  like this for a couple years)and it is being heavily loaded by discharges,
>  the plate gets dangerously orange hot.  

Yes, the plate will run much cooler in sputter or staccato (low duty
cyle) modes.  My plate runs at an acceptable orange-red color at
full power, in normal operation.

>  >>>You may remember my recent disappointing VT-27 VTTC experimental
>  >>>results.
>  
>  I have missed out on a lot of list activity this past summer because it
>  takes eons for the modem at home to download the 100's of posts (literally)
>  this list generates.  I'd like to know what you tried to do and what
>  happened.  You can direct me to the threads in the archives and I will read
>  about it. 

I guess using "VT-27" as a keyword for the archive search might work?
>  
>  I have another question for John or anyone else who wants to add their two
>  cents.  There was a small synchronous motor in the physics dep't trash
>  today (still works though), which has a disk on its axle with a little
>  cutout on its circumference that momentarily closes a 450-volt, 15 A switch
>  every time the axle makes a complete rotation.  I don't know what this
>  arrangement was for.  But I have an idea about where to use it- as a
>  cathode grounder for a staccato mode operation in the tube coil. I know
>  nothing about SRSG's, but I wanted to be able to synchronize the switch-on
>  pulse with the positive AC wave peak.  Comments, suggestions?  I need them!

I've used rotary switches rotated by a motor to create a form of
cathode staccato that way, but I never got around to trying a sync
motor yet.  My plan was to run the sync motor at 900 rpm or some
other low sync speed, to create a synchonized mechanical staccato
which would run for one AC cycle, then be off for a number of AC
cycles.  I've found that if the "on" time of the CW is too short, the
sparks are weak and spindly.  In one electronic duty cycle control
test, I kept the coil on for only 10 percent of the positive ac half
cycles (at the peak), but the sparks were thin and weak.  I also
tried keeping the oscillator running for about 30% of the positive
ac half cycle.  This gave good sparks, but the efficiency did not
improve much (most of the power is at the peak).  THis is when
I switched to the true staccato mode.

John Freau

>  
>  Thanks,
>  
>  Carl
>