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Yet even more tube coil mayhem!



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

Hi All!
    Yup, I know, ad nauseam on the tube mayhem :)

  Last night I wound a new primary/grid for single-ended operation, as I'm
still lacking MOT's for a stout DC supply. My 2 current mot's don't play
well together with a doubler circuit in place, as 1 is 1800v and the other
is 2200v.  makes about 1kv difference when the doublers are in place and
that bucks the tubes pretty badly, and limits output on 1/2 the 60hz mains.
    I didn't count turns on the grid or primary, but I'd guess about 12
primary turns (12ga THHN), and maybe 14-15 grid turns (22ga PVC hookup
wire).
    Running 2 tubes and about 1300w input to a single voltage doubled MOT I
get nice hot 6" sparks (more like a flame) from a 2.5x11" secondary (833khz
Fres /w topload).  Pretty inefficient, but at least I'm gettin' sparks and
doing more than testing the push-pull (no tranny large enough to put a
substantial amount of power into the setup in push-pull).
    Wound a new filament tranny using 1/8" Cu tubing for the high-current
windings.  Running 2 tubes for ~40 min straight was no problem and heating
was very acceptable, even under high-powered runs.
    I logged about 20 min of straight runtime on the coil at about 1kw input
with no trouble whatsoever.  With the RL chokes on the grid terminals I get
very little trash, even at 830khz tank freq.  My digital camera worked
within 3' of the coil without any trouble, and I got only a handfull of RF
burns.  One thing I noticed is that the smaller coil is *much* more tolerant
of frequency drift in the tank circuit, and Fres of the secondary dropping
when I physically get close to the coil.  Once I have plasma on the
breakout, I can turn the system down to a mere 200w and get right up on the
coil before it wavers and goes out (I mean standing right over the thing).
At 500w input after the plasma forms, the coil continues running even after
I get right up on it. At 1.3kw I don't get too close, as the coil melted the
tip off a drywall screw (I mean breakout facilitator) in just a few seconds.
Total runtime last night was about 2 hours, spanning about 5 hours of
working on it. (7pm to midnight).  no components blew up, nothing
smoke-tested, and the only problem I ran into was the tubes themselves.

        When running at any appreciable power level, I notice that 1 tube's
plate gets cherry red, while the other is still just ruddy orange.  Tonight
I'll clean the terminal clips inside and out, and try switching tubes around
so that I get them more evenly matched. What causes that?  The plates are
tied together with 1/4" copper strap connecting the plate clips, and the
tank lead is brought out from the midpoint between the tubes.  I have a
ferrite-core choke on the plate output, but the one tube runs hotter than
the other with or without the choke in place.   Tonight I'll also get the
other 2 tubes wired into the setup and it should run wide open (~2kw)
without stressing the tubes too much. Though at 1300w the primary gets
pretty damn hot!

  I also tried a quick experiment.  5 turn secondary in the primary, with
leads going to a 3 turn coil on the base of the 2.5x11  coil.  Makes a
closed, shorted circuit, I know. I was curious.  While there was substantial
current on the "driver" coil (the 1/8" tubing got scalding hot and the PVC
insulation on the leads curled back), there was *no* output from the
secondary at all.  Not even a tiny spark to a grounded rod when dragged
across the toroid. I didn't check to see if I'd thrown the system out of
tune, so I'll probably work on that more tonight also. Probably a waste of
time, but hey, it's fun to me :)

Many thanks to all who helped me get the parasitic oscillations stamped out!
Now the FCC will have a bit more difficult time  tracking me down.  Can't
wait to get all 4 tubes in parallel. [cue evil laugh]  more power!  I must
have more!!!  Special thanks to James H., for selling me that Tek scope and
sending the HV probe!  Those 2 things have made this project magnitudes
easier!
------------------------------------
Shad (Sundog)
G-2 #1203
"To call someone crazy just shows
you can't understand their views on Life."