Oh my! This is all getting rather lengthy and involved, isn't it? Also; I do not yet have the 'Quoting' functions quite sorted out... please bear with me; I'll try as best I can.
Let's see... Madkite said:
"Will let you all know my results but it will be a while because of work.
Not to mention all the other equipment I need to make like variable
inductances. The old sort with the sliding brush on a wire coil. It
saves ages of fiddling with the primary coil and it has been a nightmare
insulating a variable capacitor. The sparks go straight through all the
insulators I have tried and oil immersion seams the only option for that
and that can make for a very messy awkward to store piece of equipment."
Well; perhaps, if I may be of some advice... have you given some consideration to the thought of using a variometer in the circuit, instead? Variometers are much simpler to construct than rotary-coil inductors, and they also enjoy the added benefit of being capable of handling much higher peak currents, as there is no longer any requirement for a sliding brush or rotary contact. True, the adjustment curve is not linear; it takes the shape of an 'S'-curve instead - however, in such a straightforward application, that should hardly prove to be a detriment.
Also; with regard to the variable capacitance - perhaps you should seek a good-quality vacuum capacitor, instead? The Jennings Radio Corporation used to manufacture these devices, for use as plate-tuning elements in the power amplifiers of large AM and SSB transmitters; they were quite robust, and often had ratings in the 30-40 kilovolt level. They were manufactured in both fixed and variable designs - I recall the variable units had to be driven with long fibre-phenolic shafts, so as to not present a lethal shock hazard to the transmitter operators!
Ah - here's a smaller one, on 'eBay':http://cgi.ebay.co.uk/JENNINGS-15-KV-VACUU...2QQcmdZViewItem
Now; then, Zapper said (and I fear I shall have to divide this response into several portions!):
"Quote: MOSFET manufacturers do not yet appreciate the enormous amount of
_current_ that must be switched to the device's gate electrode, in order
to obtain short full-output pulses at the drain! I was switching well in
excess of 2 amps into the bloody thing, in order to get the pulse width
down to 60 ns and of course, eventually the internal gate lead blew
This could mean one thing - that 'longitudinal waves' could not be
produced under these circumstances since the MOSFETs needed a certain
amount of amps to switch on. In Tesla's version he never used MOSFETs or
solid state devices since they didnt exist at the time he used homemade
capacitors and a magnetic spark gap. Another thing about solid state
devices - they are very inefficient in high power output requirements
since they cannot handle such high voltage or high currents."
Well, I must admit I really do not know at all of the circumstances which may be required to produce "longitudinal" waves, as I am certainly far from being the sort of genius that Tesla was! My objective in that case was to produce the shortest possible pulse duration, obtainable only by designing the drive circuitry to produce the fastest possible switching times in the main circuit MOSFET... the 'fall' time, of course, being the most crucial, as, due to the Miller capacitance effect, a high-voltage MOSFET device becomes exceedingly difficult to turn _off_ rapidly. I was driving the gate with lower-voltage MOSFETS, and a +15-15 volt 10-amp bipolar power supply... and, it was the N-channel device connected to the -15 side that was passing the largest flow of current, by far. Incidentally; when I say a "60ns pulse" was obtained at the drain of the 500-volt device, that pulse width was measured at very nearly the ground level, not halfway up the slope. The best 'rise' time I obtained, as I recall, was something on the order of 16ns from ground to +500, and the 'fall' time was slightly more than 25ns.
"Quote: the lamp dutifully glowed quite purple in response
could it be that there was a voltage spike at the beginning that was
high enough to ionised neon to form a purple colour?"
Yes; that was the idea, of course. You see, when such a lamp is operated "normally", the first-level ionisation establishes a voltage drop of about 90 volts between the electrodes, and this drop is quite independent of the lamp current - the current may be increased or decreased over a fairly significant range, yet the 90-volt drop will remain constant - this, in fact, was the operating principle behind the "VR" voltage regulator tubes that were formerly employed to maintain stable screen and plate voltages throughout the era of vacuum-tube radio, long before the solid-state Zener diode regulators came about.
However; in measuring the drop across the lamp in my circuit, I was pleasantly surprised to observe that the 'standard' first-level voltage drop was being bypassed entirely! I employed a good-quality oscilloscope for the measurement, with a rather expensive 'fast-response' low-capacity high-voltage measurement probe, and although I had expected to see at least some sort of a "bump" in the waveform at the usual 90-volt level, there was indeed no such "bump" whatsoever - the voltage rose smoothly all the way up to 500 volts, directly across the lamp electrodes! My guess at the time was that perhaps the pulse duration was so brief that the gas really may not have had sufficient time to enter fully into either first-level or second-level ionisation... which (if I may be allowed to digress somewhat?) brings to mind another interesting point about spark-gaps in general: because they depend on ionisation for conductance, they are relatively 'slow' devices, with switching speeds generally measured in milliseconds (although the thyratron gas tubes employed in radar pulse work did get down into the range of several microseconds, because they utilised hydrogen - the lightest gas, having, of course, the most mobile of ions.). And this also restricts the operating range of "traditional" Tesla devices to the lower frequencies only - it is not the principle, but rather the means of switching the current that becomes the problem, in attempting to raise the operating frequency (and thus reduce the size of the device.).
"Quote: use semiconductor lasers to switch a symmetrical bi-directional
intrinsic channel directly?
That would do a better job anyway... Not much i can say on this aspect
of lasers since i dont know much about them... perhaps you could give me
a link that explains the implications of using laser technology in place
of solid state devices."
No, unfortunately I cannot, as that technology does not yet exist - it is merely a thought I've had, for some time; the notion that perhaps instead of using a metal or polysilicon 'gate' electrode to induce conductance in the main silicon channel of a FET device, the electric field of the photons produced by a semiconductor laser (in the same package, much as in the case of an optoisolator, and shone directly at the main channel) could be employed to induce the conductance directly.
However, there is at least one reference that comes to mind of lasers being used to trigger conductance in _ionisation_ ("spark-gap") channels directly, and that would be this one:http://www.sandia.gov/media/images/jpg/Z.jpg
Oh - sorry; that's the picture (an old link I had, laying about)... this is the reference:http://www.sandia.gov/media/z290.htm
"By the way I remember reading in one of Tesla's books in which Tesla
said repeatedly that it was crucial to copy his electrical apparatus
exactly (not in size but in proportions)."
This was likely because the Q of a resonant circuit inductive element is determined, I believe, by the ratio of instantaneous AC impedance to the intrinsic DC ohmic resistance. In other words, in order to obtain a high value of Q in a coil, the wire must have the _lowest_ ohmic resistance possible - and thus, be quite *thick* of gauge.
The first "Tesla coil project" I attempted was when I was rather young; it was an article that appeared in the magasine 'Popular Electronics', sometime during the 1960's. The design employed a far-too-long secondary coil that consisted of very _fine_ gauge wire that was close-wound on a waxed cardboard tube, and driven by an 811A transmitting tube in, I believe, a Hartley oscillator circuit driving the primary. It was far too low in Q to be efficient, and the results were not very spectacular. I believe the author may have been labouring under the (incorrect) impression that a "Tesla coil" should be acting as an electrical transformer, perhaps? Tesla, on the other hand, used heavy-gauge spaced-wound wire on large-diameter open wooden frames - and of course, obtained much more satisfactory results.
"Quote: they do not even have to be coils at all - exactly the same effects
can be produced with a low-loss narrow-bandwidth end-fed quarter-wave
antenna wire... and (perhaps?) I might suspect, a quarter-wave waveguide
resonator as well?
Hmmm.... there is a downside to this design - you would need an
extremely very long antennae if you wanted it to be between MHz and Hz
range. There is also another aspect to that design - it changes the 'Q'
property of the resonator from a high Q to a low Q, thus have a very low
self capacity - that means it would resonate to the vibrator or primary
but would not manifest sparks because 99% of the energy stored would be
in the form of hertzian radiation that would escape from the wire (radio
It is indeed difficult to obtain a high value of "Q" in a longwire quarter-wave antenna, primarily because the conditions for such are quite contrary - in order to achieve the narrowest bandwidth (and thus the greatest amount of resonance, the "equivalent" of Q) in such an antenna, the aspect ratio (of length to wire diameter) must be as large as possible. In other words, this results in a very fine wire gauge along a rather long length - with consequently high ohmic losses.
Nevertheless, a fairly decent compromise may indeed be obtained - and it is a well-known fact that the 'open' end of a quarter-wave antenna will develop a _much_ higher voltage than the 'driven' end, due to _impedance transformation_... and impedance transformation, of course, is exactly what a Tesla resonator is all about.
I seem to recall reading once somewhere, that during the very early days of trans-oceanic underseas cable telecommunications, the keying rate of the Morse code sequences had to be closely watched and regulated, lest the voltage at the receiving end be built up to such an extent that the receiving station apparatus may arc over disastrously, and be burnt-out!
"Tesla modified his antenna to a coil so they could hold alot of energy
for a certain amount of time and release it in one huge dump - the
manifestation of electrical sparks often exceeding the height of the
coil as well as a lot of radio waves."
Well; the "certain amount of time" would, of course, be one-fourth of the full cycle of the resonant frequency - the direct physical analogy would be akin to cracking a whip. And the "amount" of energy stored in a coil is directly proportional to the physical size of its construction.
"Quote: the "Terry Tetzloff" character in the "Duckman" cartoon series."
Hmm? I'm sorry; did I say that? I don't seem to recall... oh; no, I see by scrolling, that it was that "Guest" fellow... I'm afraid I don't quite understand this; could someone please tell me what it's about? I've not yet had an opportunity to view that particular 'cartoon series'.
"Also the creator of frankenstein was copied after Tesla. Hint: lightning
bolts from sky to a high metal tower connected to Frankenstein awaken
him. 'Im aaaliiiive!""
Oh, no! You've got it quite reversed, I'm afraid - you see, it was _Frankenstein_ that was the creator... whereas his creation, according to the author, was not bestowed with any name; it was simply referred to by the popular press in those days as "Frankenstein's monster".
I'm not quite certain, but did Mary Shelley not precede Nikola Tesla by a generation? I'm not sure they were contemporary...
Oh well! This is all so very interesting... I do hope these discussions may assist with your experiments in some way. They are certainly fascinating, at any rate, and I wish you both success!
Best regards towards all -