Re: TSG instability

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Gary,

Been awhile since I've played with my Tebb's TSG (get too many projects
going at one time), but
if memory serves, I was experiencing the same behavier. At the time, I
thought the 555 was
cutting out. I'd recommend scoping the trigger starting at base of Q3 to
see if the trigger
didn't make it out of the 555 (should coincide).

Take care,
Bart

Tesla list wrote:

> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
>
> I have been making slow progress with my triggered gap experiments.  I use
> a modified Jon Tebbs zero-crossing detector, driving a capacitor-discharge
> circuit to power an EG&G trigger transformer.  The circuit works well,
> delivering a consistent 3/8" spark regardless of the phase control setting.
>  All of my experiments so far have been done using an array of halogen
> lamps to serve as a dummy-load in place of my primary coil.  This works out
> well as the lamp brightness directly indicates the phase "sweet spot" and
> is far less subjective than streamer length.
>
> While I'll ultimately be interested in finding the least lossy electrode
> configuration, I've been stumped by instability when approaching the timing
> sweet spot.  Just as with a mechanical synchronous RSG, the lamp brightness
> increases as the trigger delay increases, approaching the sweet spot.  The
> sound of the gap is a strictly even drone.  Scoping the gap waveform, the
> gap is firing as the gap/cap voltage is still increasing.  Increasing the
> delay, the lamp brightness continues to increase and the gap fires as the
> waveform crests.  But now, every second or so, the gap misfires.
> Continuing to increase the delay, the brightness increases considerably and
> the gap fires as the waveform is on the downswing, but the frequency of
> misfires increases correspondingly with the delay setting.  Clearly, from a
> performance perspective, the gap should be firing at this point, but the
> misfires cause dangerously high voltages across the cap.  If I was using my
> primary and secondary rather!
>  than a dummy load, racing sparks would surely result.
>
> I wanted to ask other TSG users what their experience has been with regard
> to this instability.  I don't think my trigger circuit is misfiring when
> the NST is drawing maximum current and causing the mains to droop.  The
> 300V capacitor discharge power supply dips only a few volts when the
> instability is at its worst.  I have verified that the timing is stable
> across a wide latitude of AC input voltages.  That the timing vs.
> power-delivered and stability is so similar to a mechanical SRSG, it makes
> me wonder if there is some mechanism inherent in sync gaps that can't be
> overcome.  But I don't want to believe this.
>
> I'm using a 15/60 NST with a .03uF cap, for about a 3X LTR factor.  Since
> the instability seems most evident when the timing is beyond the crest of
> the cap voltage (optimal for LTR operation), it seems that LTR operation
> may be a factor.
>
> Regards, Gary Lau
> MA, USA