Re: vttc video....

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 2/11/07 1:32:41 AM Eastern Standard Time, 
tesla@xxxxxxxxxx writes:

> >Dan added
> >some extra features too.
>
> I am very excited about those extra features.  Does it
> allow you to control "dwell time" as it were, or pulse
> width...is that how I should refer to this?


Brett,

The extra feature permits trains of pulses within longer pulses.
For example one can obtain 4 pulses of 30pps, then a delay
equivalent to 20pps, then back to 30pps, that sort of thing.
The regular staccato board can't do that.  It offers only
only a particular pulse rate when set to a particular pulse
rate.

However in all cases, the on-time is always a full 120Hz AC
half-cycle.  This is because the SCR that controls the
tube cannot shut off while the tube plate has positive voltage.
The SCR cannot act fast enough.  The job could be done
using a hydrogen thyratron, or maybe with some new type
solid state device.  In my early experiments using duty cycle
control, I managed to shut off the coil during the positive
half cycle using a vacuum tube to control the staccato by
controlling the grid bias.  Using this method could destroy
the main tube grid however.  It may be possible to delay
the turn-on of the tube until after the positive ac half cycle
begins, similar to the way lamp dimmers work.  I didn't try that.
In any case duty cycle control was very disappointing.  Although
I ran the tube for only a short duration during each AC half
cycle, the input power didn't decrease very much.  The
sparks maintained most of their length, but became very dim
and weak looking.  It was after I saw how poorly that worked that
I came up with the staccato idea.  However on a very large
vttc (which would tend to have brighter sparks anyway), the
idea might be OK.  The biggest weakness of duty cycle
control is that it's cutting off the weaker parts of the RF
envelope (the beginning and end of the envelope).  The power
is weak during these times anyway so not much power is
wasted.  These weak areas do however contribute to
the brightening of the spark.  Thus one gets a bright spark
(using staccato) while wasting very little energy.  This is
the beauty of using the staccato system.

John


> -Brett
>
> >
> >John