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How to rise the secondary?





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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Monday, June 29, 1998 6:50 AM
To:  Tesla List
Subject:  Re: How to rise the secondary?

John, All

There are two reasons one might want to adjust the coupling by raising
the secondary: 
1. to adjust for secondary coilform insulation withstand capability
2. to match the coupling to the capability of the main gap and streamer
loading for best system quenching. 

When the secondary is overcoupled, the usual obvious symptom is unwanted
electrical breakdown between portions of the winding - sparks
periodically "racing" from the portions of the secondary winding to
other portions. Previously, this was thought to originate from the
effects of greater "frequency splitting" under heavier coupling which
presumably created a 1/4 wave voltage peak at a point below the top of
the secondary winding. However, with the latest measurements made by
Terry Fritz showing mostly lumped parameter (LC) behavior, it's not
clear that this is the root cause. In any event, raising the secondary
typically will reduce the voltage stress across the secondary to stop
this behavior. Since the voltage withstand capability of a secondary is
a function of the construction technique and type of wire, and not
easily predictable beforehand, it's sometimes necessary to "tweak" the
coupling.

The other reason is to "tweak" the system for maximum spark under full
power and full topload. A well-constructed secondary may show no signs
of coilform voltage breakdown but may still be overcoupled. Best coil
performance is usually obtained when the primary tank's energy has been
transfered to the secondary and is then "stranded there" to be
dissipated in streamers. This occurs when the combined effects of
optimal topload, streamer loading, and the inherent quenching capability
of the primary spark-gap conspire to inhibit reignition of the main gap
once all of the primary tank circuit's energy has been coupled to the
secondary... a "perfect quench". 

Since the effects of streamer loading and gap quenching are difficult to
predict beforehand, "tweaking" of coupling may be necessary to wring the
last ounce of performance out of a system. BTW, there seems to be
significant empirical evidence that most systems (mine included) tend to
quench suboptimally until running at maximum power/max streamer loading. 

Safe coilin' to you!

-- Bert --


Tesla List wrote:
> 
> ----------
> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Sunday, June 28, 1998 12:23 PM
> To:  Tesla List
> Subject:  Re: How to rise the secondary?
> 
>   Ed, All -
> 
>   What are the advantages of raising the secondary? This will change the
> coupling and tuning but that can be done by proper design of the primary. Or
> have you found other reasons for raising the secondary?
> 
>   I would expect that moving the secondary away from the primary would
> reduce the spark output.
> 
>   John Couture
> 
<SNIP>