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Re: Primary Scoping

On the subject of scoping the primary, Jim wrote....

>         I was woundering if anybody had hooked a high voltage divider up to
> the primary of a TC and observed the waveform, measured the spark gap quench
> time or performed any other measurements? I've got an 20KV RF rated voltage
> divider and a dozen or so Dale HV-2 100Mohm resistors. Any thoughts on
> safety? I'm a degreed EE but haven't done any HV work and want to make sure
> I'm safe before I'm sorry.

I have scoped primary operation and am shortly about to do more, but
first - I haven't scoped one using a resistive divider. I have used
Mark Barton's technique of dangling an aerial from the scope lead
some way off to see what was happening. Very interesting indeed. The
scoping was only done with single-shot operation. I haven't yet
scoped a coil under AC running conditions. Also, I haven't run a
quench gap as yet. BUT, I have determined the ideal quench time for
my large coil for the value of k it is set at. The time turns out to
be about 25uS. In the coupled system, you can see when the secondary 
ring-up has reached its peak. You ideally need a storage scope for
this but I think you could just get by with a standard one.
     I am shortly going to calculate the frequency split values (ex-
pressed as F(hi) = yF(lo) where y is a multiplier) for the sweet
values of k. I'll post when I've done it. Knowing the correct fre-
quency split will enable coupling to be tuned to a particular
value BEFORE power is applied to the coil.
     I AM planning to directly scope a primary with a divider under
single-shot conditions with the secondary in-circuit to try and
clear up a mystery that has been puzzling some people for a while.
I don't want to elaborate at the mo.

> I have thought about using a 1000:1 divider ratio using 4 of the 
dale
> 100Megohm resistors in series to a  5 parallel combination of 2megohm carbon
> comp resistors. I'll then put some transorbs to ground before the scope
> connection. All components will be physically well mounted to prevent
> circuit disconnection.
> BTW, transorbs can be thought of as a 5ps.(thats not a typo: 5*10^-12
> second) zener with a many thousand Amp ratting. By using 2 of the
> unidirectional devices in antiparallel I can get any clamp voltage between 5
> and 500 volts with only a 200pF capacitance penality. 
> 
> I still have to reduce my common mode power line noise, it's getting into
> the scope with the scope input switch on ground and no probe cable
> connected. I do have 1 heavy duty line filter in series with the neon.
> 
> Any thoughts, physical barriers, components?

Please keep us posted on this. I am VERY interested.

Malcolm