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Re: Beginner Measurements

Tesla List wrote:
> 
> Quick and Dirty resonance check
> 
> >From jparisse-at-ddlabs-dot-comWed Oct 23 21:37:51 1996
> Date: Wed, 23 Oct 1996 10:49:27 -0700
> From: "Jeff W. Parisse" <jparisse-at-ddlabs-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Beginner Measurements
> 
> All,
> 
> I just started using a tip from Richard Hull to measure the resonant
> freqs of our tesla coils and I feel as if I've discovered the "next
> level" (a self realization... I know you guys already know this stuff).
> I'll repost the tip at the bottom of my post...
> 
> My questions are... Now hungry for more actual readings (instead of
> computer projections or forumlae) I want to know if there is a way to
> measure primary resonance with a VOM, Frequency Counter and Frequency
> Generator (old Heathkit 1Hz - 1MHz, 10V)? Can one use measurement
> techniques to pinpoint the tap point? Is ther a way to measure the mH of
> a particular primary coil. Since inductance increases as one moves a tap
> along the primary and the resistance of the primary conductor increases
> too, wouldn't it be possible to somehow relate the two in an effort to
> measure resistance to infer inductance?
> 
> Jeff W. Parisse
> www.ddlabs-dot-com/tesla/
> 
> PS Thanks Richard...
> 
> Subject: Quick and Dirty resonance check
> 
> All,
> 
> We have used a really trick, used for years here from finding resonant
> frequencies.  No scope or meter required. You need only a good frequency
> generator.  We prefer the old clunky ten ton vacuum tube Hewlet
> Packard units of the 50's and 60's with 50 ohm output impedances.
> 
> Buy two real good (expensive) radio shack ultra bright red LEDs.  Hook
> them in parallel, but reversed anode to cathode.  put the pair in
> series with the hot line of the generator and hook to the base of the
> coil under test. (ground the generator's negative or common lead)  I use
> a full 5 volt RMS output signal from my generator.  Tune the generator
> until the leds are at their brightest and then read the dial. (assumes
> dial is fairly well calibrated.)  This is just tuning until max base
> current flows (resonance)
> 
> Note!  A modern 600 ohm generator can be used with reduced brightness.
> A single LED will also work.  The key to success is a healthy voltage
> output from your generator and ultra efficient LEDs.
> 
> Therefore, the first major hunka' test gear for the coiler after a good
> meter is a good signal gen.  A scope should be way down on the buying
> list for a beginner.
> 
> Richard Hull, TCBOR

Richard,

The problem is that its very difficult to acurately measure the LOW
resistance of a typical primary. Even if you could, the inductance does
not linearly change like the resistance does. However, if you have the
signal generator and frequency counter, you've got all you need.

The approach descrivbed by Richard works for the primary, but in a
reverse sense. Remove the secondary, disconnect any safety chokes/caps
from the tank circuit, and place a short across the spark gap with a
piece of wire. You should now have just the parallel combination of the
tank cap and primary. Hook the ground of your signal generator to the
inner end of the primary, and the "hot" end, through the back-to-back
LED's, to your primary tap. Slowly increase the signal frequency until
the dimmest point is seen on the LED. This is the point of
"antiresonanance"  - the parallel LC freqeuncy of your primary tank. You
want to initially set this to be the SAME as the isolated
secondary/toroid pair's natural frequency previously as Richard Hull has
described in his post above. (When you actually run you coil, you may
have to "tweak" the tap from this "instument tune" position for best
results).

Now you can re-install the secondary/toroid back to its normal postion
inside the primary, but don't hook up the base ground yet. With the
secondary in position, and the primary sparkgap still shorted, measure
the points of maximum LED brightness. You should now see TWO frequencies
where the LED is brightest. Record these as Flow and Fhigh. The coupling
coefficient can be approximated by (Fhigh-Flow )/Fcenter. Now disconnect
all mesurement setups, move the equipment to a safe area, and fire up
the coil for best actual tune. Enjoy!

Safe (and measured) coilin' to ya!

-- Bert --