From: FutureT@aol.com
Date: Tue, 14 May 2002 12:15:13 EDT
Subject: Re: [TSSP] Topload breakout potentials, etc.
Paul, Malcolm, Bart, Boris, all, Tests and comments. I did some tests with a 6" x 24" smooth toroid installed onto the TT-42 TC. I first removed the 4" x 13", but left the small 1.5" x 6" toroid in place. The bottom of the new large toroid is 3/4" above the top of the secondary winding. I first tuned at 16.5 turns (76uH), this barely permitted the sparks to break out at full power. Sometimes break out was delayed for 10 seconds or so. One time the breakout stopped, while the coil was already breaking out. So this seems to be right at the edge of breakout. The sparks seemed to be about 42" or so. Next, I tuned at 15.5 turns. The sparks could not break out. Then I tuned at 17.5 turns. The sparks could not break out, so I added a breakout rod over the toroid edge. this permitted breakout, and the sparks were longer at 44" perhaps or longer. Next I replaced the breakout rod with a breakout bump made of aluminum foil. The sparks broke out and I measured a 44" spark. The spark hit the measuring wire with good energy, so it could have gone further. Maybe they could have reached 46". I didn't want to run the coil too long for fear of destroying the NST. It has no protection networks. I tried tapping at 18.5 turns, but the sparks were weaker, and still needed the breakout bump. It seems that a toroid which can only break out when in perfect tune (if it is perfect), gives longer sparks when tuned outwards even more, but with a breakout bump installed. In all cases of breakout, there was only one streamer. This proves that the spark length improvement with lower freq tuning, was not due to a reduction in the number of streamers No racing sparks occured during any of these tests. Using the larger toroid, the streamer C is a smaller % of the total secondary + toroid + streamer C, so the coil should need less downward tuning for this reason alone, if not also because the need to delay the breakout is eliminated (unless the reason for detuning is the offset idea that Malcolm mentioned). Would the concept of the need to delay breakout even apply, if a breakout bump is used? It would seem to negate the need somewhat. Regarding the idea of tuning to compensate for streamer C, someone on Pupman once suggested that the reduction in Q with breakout should make the tuning rather non-critical. If it's really very non-critical, then perhaps the lower tuning is needed for a different reason, such as that mentioned by Malcolm, or simply to delay the breakout. Whenever I saw racing sparks in the past, they were usually just an inch or two long. The type that reach the full length of the secondary occured only when the coil was severely overpowered, or when the coupling was extremely tight. If the racing sparks are caused by higher frequecies from the primary, maybe they can be filtered out somehow? An interesting test would be to use a sphere or near-sphere which had the same C value as the 13" toroid, but had a large ROC which gave only one streamer. This would tell us how much spark length is gained by having only one streamer, but keeping topload C the same. Cheers, John
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.