[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Tube Coil, impedance matching



Original poster: "sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

Hi All!
 
 Still tinkering with the tube coil, and having a blast. (most important part
of coiling)
 
  Where can I find a crash course in impedance matching,  or can someone
willing to educate this non-EE a bit in how to figure out some of the necessary
stuff contact me off-list?   Being the sysadmin for a large Unix network has
nothing to do with impedance matching, therefore I know very little about
impedance matching :)   Anywho!
 
  After airing out the garage and replacing the smoke-tested line filter, I
fired off the tube coil again.  About 5 sec into the run the grid coil flashed
over, scorching the side of the primary form and generally irritating me
(there's a finite amount of smoke you can let out of a system before it dies
totally).  I cleaned up the primary form with the dremel and acetone, and
re-wound the grid coil with 20 turns of 20 ga magnet wire (vs 12 turns of 22ga
hookup wire).  The new grid coil is about 1" above the primary, whereas the old
grid coil was about 3" away (above).  
 
  I am now using a single 833 to drive the coil also.  There's less radio
interference (barely a buzzing), and the coil seems to run smoother.  The tube
gets hot (the 2 tubes ran dark, one gets a muddy dull red), but well within
it's limits. 
 
   I added more grid C in series to drop it to ~1.5nf, and my problem of the
grid R smoking (and catching fire) are all but gone.  Now it takes ~2 min (vs
20 sec) to toast a resistor. Coil operation also smoothed out a bit more.  I'm
going to try adding some PFC to the MOT, to see if that eases the current
draw.  
 
    I've noticed one odd thing - The coil seems to run a LOT better the more it
gets loaded down by sparks, but not topload.  Sparks to air are about 6-7" (and
just too cool lookin').  A spark drawn to a metal rod (grounded) has the same
white-orange intensity of a NST's arc, and can get about 8" long.   A jacob's
ladder (wire on the topload, grounded wire that comes close to the topload and
they go up in the typical fashion) looks awesome and seems much more wicked
than you'd expect it to.    Very cool!   I finally had to call it a night about
11pm, but not from noise or TVI, but the 'skeeters were getting too thick to
comfortably work.  
 
  So, any takers on teaching impedance matching?
                                                                           
                                                                Shad