RE: [TCML] Oscilloscope methods for showing Ringdown

["Lau, Gary" <Gary.Lau@xxxxxx>]

I think you're going to have a problem attempting to use the primary-side voltage to trigger the scope.  With a static gap, you're going to get many voltage peaks that come very close to the gap breakdown voltage, but don't actually result in a bang, resulting in false triggers.  And as you alluded to, having a physical connection to the primary can be hazardous to you and your scope!

I've never had a problem using a probe or wire capacitively coupled to the secondary field trigger the scope, and yield a stable display on a non-storage scope.  Only one channel is needed - nothing could be simpler, safer, or more stable.  There will be some jitter, as the static gap bangs will not all be identical in size, but you'll still see what you're looking for.

You scope DOES have triggered sweep (only sweeps following the trigger voltage exceeding its threshold), right?  If not, you would do well to get a 465...

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Phil Tuck
> Sent: Thursday, March 12, 2009 8:06 AM
> To: 'Tesla Coil Mailing List'
> Subject: RE: [TCML] Oscilloscope methods for showing Ringdown
> 
> Hello.
> In reply to DC's idea I forget to mention that I had already tried running
> the coil at low bps on the Variac. I can get it to run on 50v (20% power)
> when it fires at the rate, and also sounding like, a machine gun from a
> World War 2 film, and still with a healthy spark.
> Five or six bps?  It's very difficult to tell without recording the sound
> and analysing the waveform. Anyway the trace from the individual firings is
> so quick that the scope barely shows it - unlike a storage scope would. So
> the one-shot mode I think will fail, but I have seen some HV diodes on Ebay
> that I'll try.
> The scope's tube is rather tired as a faint 'quick' trace can be hard to see
> on max brightness. The gap is static as Gary guessed so syncing to the mains
> won't work. I am altering my voltage divider to attempt to get a low enough
> signal to allow the SG to do the triggering - should be interesting. Has
> anyone managed that and still left the scope working?
> I could do with a duel channel model really, so the SG trigger idea might
> mean I have to actually get one (plenty of Tek 465's on Ebay usually)
> 
> Regards
> 
> Phil
> www.follytowers.co.uk/tesla
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Lau, Gary [mailto:Gary.Lau@xxxxxx]
> Sent: 12 March 2009 00:53
> To: Tesla Coil Mailing List
> Subject: RE: [TCML] Oscilloscope methods for showing Ringdown
> 
> If one is using a static gap, this will not work.  With a static gap, the
> timing is totally unrelated to the mains phase - it's purely chaotic.  Only
> if one is using a synchronous rotary gap will the gap firing be related to
> the mains phase.
> 
> It properly answer the question, we'd need to understand exactly what the
> goal is.  If it's just a qualitative observation of the secondary ringdown -
> like to determine 1st/2nd/3rd notch quenching, you shouldn't need anything
> more than a standard triggered sweep scope, with any type of probe just hung
> in the vicinity of the secondary.  Just sync on the pickup probe and play
> with the trigger level.  Even with the chaotic firing of a static gap, the
> scope will trigger at the same point of each bang.
> 
> Regards, Gary Lau
> MA, USA
> 
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > Behalf Of Skip Malley
> > Sent: Wednesday, March 11, 2009 5:18 PM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Oscilloscope methods for showing Ringdown
> >
> > For scope triggering, try to sync the scope to the power line.  Your
> > spark will likely happen at the same phase point of the AC.  You can
> > vary the phase and trigger point along the AC waveform.
> >
> > Skip
> 
> <snip>
> 
> 
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