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Offline ake003Topic starter
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« on: February 04, 2016, 11:14:18 pm »
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Hi everyone

I have build a Change from Silverdog.com and I have a problem with the calibration of the dump resistor to measure with the oscilloscope.
Where and how do I need to connect the probes to get it correct? I would be happy to get connection points on schematic or picture.
The coils I have are (1.2 ohm / 400uh 0.35mm) and the other coil is (0.8 ohm / 398uh 0.8mm). (they are 8 inch)

I have been using two 1k2 2Watt resistors with potentiometer(5k 2Watt) connected to the point to the dump and oscilloscope to measure.

On the Russian web site there is information (

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http://fandy.hut2.ru/Chance.htm
), The voltage across the coil (point X1.1, yellow trace) and the shape of the current through the coil (blue ray). General form. For the current measurement series with the coil it is necessary to include a resistor of 0.1 - 1 ohm, and watch the voltage on it.

I don't know what I'm doing wrong?
Maybe someone can help?


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Offline Homefire
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« Reply #1 on: February 05, 2016, 11:08:26 am »
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  Basically You just use the scope to measure the FlyBack adding resistance until the ringing just stops.  Most set up are a off board  Pot,In place of said Resistor scope on the out put of the fist amp.  This way your scope is protected by the Limit Diodes and Amp, and your seeing what the detector is seeing.    Your going to see the ringing on the signal the detector is using.  Now Measure what the POT is set at and Use the Closest  resistor you can .    Easy  Pie.

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Offline ake003Topic starter
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« Reply #2 on: February 06, 2016, 01:43:48 am »
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Thanks Homefire,

I will test to measure from out put of the fist amp to see if it will work.

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Offline GoldDigger1950
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« Reply #3 on: February 06, 2016, 06:45:25 am »
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Something else you may want to keep in mind is that some points are what are known as "current nodes" versus voltage nodes. Voltage nodes reveal a changing voltage pattern that is visible on a scope while current nodes appear to be completely dead - no voltage at all. On those, the current varies by amplification rather than the voltage. You cannot measure those points with a scope.

So, the best solution for you is to look around and see if you can find a video showing how to do the measurements and what to expect. As I recall, Silverdog made some videos to help builders. Look on YouTube for assistance.

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Offline ake003Topic starter
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« Reply #4 on: February 10, 2016, 01:57:10 am »
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Thanks for all your help.

Unfortunately I could not find any videos on YouTube.

After some hours work I found out if I change the guard interval between 19 and 20, it was like a break point where the signal is correct and under 19 it is running.
The flyback resistance was 511ohm. But the problem is getting the exact resistance, two resistances parallel and I got 516ohm.

The sensitivity with the aluminium sample that I used (1.5cm2 in measurement) was 2cm from the coil before I got a reading.
 Smiley

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« Reply #5 on: February 10, 2016, 09:28:32 am »
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Emmmm    Looks like you have some tweaking to do.   

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Offline ake003Topic starter
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« Reply #6 on: February 10, 2016, 07:28:38 pm »
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Sorry I forgot to write, the sample was alumni foil.

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