Re: Tube coil funkiness

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "R Heidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

on 11/12/01 11:45 AM, Tesla list at tesla-at-pupman-dot-com wrote:

> Original poster: "Sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <sundog-at-timeship-dot-net>
> 
> Hi All!
> 
> Well, I'm on vacation, so that means I get nearly a full week of
> nothing but TC'ing!  Muhahahah!!!!
> 
> Last night I sat down and tried to figure a better way to get my tube coil
> tuned.  I'm no genius, but I am armed with a signal gen and an o'scope ;)
> 
> I put the secondary in place in the setup and basefed it with the signal
> gen.  I fed the signal gen's signal to ch2 and my antenna to ch1.  Tinkering
> with my scope found a menu packed with stuff for it to measure for me (RMS
> voltage, pk-pk, period, freq, etc.)     Anywho!
> My secondary's Fres dropped considerably in the setup, but no matter, I made
> a note of the frequency (359khz). 10khz either way it dropped off a *lot*.
> 
> I then removed the secondary from the setup, moved the antenna to ~1' away
> from the primary, and powered up the system to ~1A input.  Just enough to get
> a
> solid oscillation from it.  After fooling with the trigger level, I got a
> *very* solid waveform on the scope.  Then it was just a matter of shut it
off,
> move the primary tap, do it over, till I got the frequency to 350khz.  I then
> moved the scope outta danger, put the secondary back in place, and fired 'er
> off.   All in all, it was pretty anti-climactic.  I still have a big problem
> with the grid leak network (new cap and resistor time, I'm tired of messing
> with it).  But at least I got a couple of inch sparks out of it instead of
> just some fuzz.  It's behaving like my filament transformer isn't properly
> grounded.  Strange, that's for sure.  But I have 3 more 833's to try in it,
> plus I now have a way to accurately tune a push-pull setup (testing 1/2 the
> primary at once).  One thing to look out for!!  In my previous tests, I
> removed
> the tank cap and let the other half of the primary float.  It looks like it
> autotransformered to some nuts voltage (or maybe some fluke resonant thing)
> and
> blew a thick 2" spark against the primary form.  Not pretty, but fixable.
> 
> What exactly determines grid current for the coil?  The ratio of turns of
grid
> to primary?  size of the grid cap?  It's really high for the 833, and I don't
> like it bein' that high. Bad for the tube.
> 
> Shad
> 
> 
> 
Fillament/cathode grounding is important in any tube circuit. The grid leak
voltage is determined by your grid coil turns, your capacitor size, and your
grid blead resistor to ground.
  Robert  H