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

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

Yikes! Sputter mode will certainly provide you with some excitement! This 
is something I played around with after John Freau mentioned his 
experiments. I was able to get a almost Staccato type effect of 14-18" 
sparks, I went for higher capacitance in the grid, then you. Only I do not 
play with this novel way of running a tube coil, due to it's detrimental 
effects on all "expensive" components... The only times I have had tube arc 
over was in sputter mode, not good for the tubes, :-o  Also blew internal 
HV leads on a large plate trany due to current surges from this mode. Yes, 
your plates will run stone cold (as with "true" Staccato mode, low duty 
cycle), but due to the random nature of the pulses you will get some nasty 
kick back. Seriously recommend using Dave Sharpe's 556 Staccato pulsing 
(actually in phase to the 60 Hz wave form) of the cathode over this. I have 
a pile of dead 833's (about 6) from play'in (all were pulls). Had one that 
worked great for almost an hour of total run time after a hole the size of 
a Nickle showed up in the center (833A, of course!).

Hey, anyone have a good simple schematic (design) for a audio amp utilizing 
a triode (833, 304, etc)? Please reply off list.

Here's to dimmin' the lights, and keeping those plates cheery!


David Trimmell

At 07:55 PM 9/1/00, you wrote:
>Original poster: cwillis-at-guilford.edu
> >>>Are you using a very long time constant in the grid leak network to
> >>>create pulsed operation (grid blocking)... what I used to call the
> >>>sputter mode?  I no longer use such a mode.
>Yep, I use the sputter setup still- 40 kOHM, ~.002 microfarad.  That is
>indeed a big RC.  I can select my sputter frequency by selecting more or
>fewer parallel capacitors for C.  I get characteristics of disruptive coils
>when the sputter frequency is low (capacitance high, like .004).  There is
>a lot of bluish-white corona and white thin streamers from my breakout
>point.  With less capacitance, I get tube-coil-style fiery arcs and
>discharge.  These get thicker and shorter (.0001 microfarad) as I keep
>increasing capacitance and the coil moves towards more of a CW oscillator.
>I like to run somewhere in the middle where the arc is thin but still
>substantial and violety-orange.  this is also where I get the longest
>sparks with my sputter arrangement.
> >>>Are you sure the coil is tuned very precisely?  I would expect at least
> >>>a 19" discharge using the nail.  Streamers should be somewhat straight
> >>>not too fuzzy.  Also grid feedback, grid leak resistance, etc, are all
> >>>adjustments.  I never run without the breakout point, except at low 
> powers.
>It is capable of being tuned precisely (with a transmitting air variable
>submersed in mineral oil in parallel with an MMC), but the tuning that
>works well for one type of discharge (20" horizontal arcs out to my hand
>from a point) does poorly for the other (brush discharges). I can make a
>brush about 20" long come off horizontally from the nail when I retune to a
>higher primary frequency.  Its multiple branches are long and thin, not
>fuzzy, straight, pretty much as you describe.  They will hit my hand if it
>is in range, just like the brush hitting Robert W. Stephens' ground
>terminal in his pictures, but they act like "they don't care" if your hand
>is there or not- they get no longer to reach out to it and they don't bend
>around to hit it.  They are more or less straight, and if they are already
>headed towards the conductor they hit it. Whereas, with the tuning I like,
>the brush is small but when my hand comes out towards the coil it lengthens
>and goes for contact, forming a single streamer.
>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.
> >>>I never run without the breakout point, except at low powers.<<<
>I avoid this also, because it corresponds with flashover in my tube.  Makes
>a spattering, barely visible breakout all over the toroid and the top lead
>of the secondary, usually accompanied by the occasional "ping!" from the
>tube. When it is all tuned up to do this, I can't bring metal or hands
>toward the coil without detuning it enough that the breakout stops.  I run
>at low power with no breakout (variac at 70-80 volts) to light up discharge
>tubes and play with the radiation field.
> >>>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.  This is why I made a heatsink that
>I still use for the plate pin out of aluminum to protect the seal, though
>it is completely unnecessary and unsightly.
> >>>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 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!