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Old 15th April 2005, 03:33 PM   #11
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The first stage should be ok..drawing 4mA roughly

I=V/R
0,004A=3V/750R



the second stage is running a whopping 29mA?
0,029A=6,5V/220R


must get blistering hot R5????..or my calcs are wrong......

so something is wrong with the second stage because it should be drawing around 9mA (0,009A=2V/220R

the first stage is supposed to draw 1,3mA
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Old 15th April 2005, 03:45 PM   #12
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Yeah, I've double checked R3 & R5 and measure with the Multimeter. I'll check again when I get home. I've tripled checked all the wiring but I'll do that again as well.

Would increasing R5 make the voltage go down? Sorry, I'm such a newbie I have to confess I don't understand what drives the voltage at that point in the circuit.

Thanks.
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Old 15th April 2005, 03:56 PM   #13
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Ooh...I don't fully understand it either..a bigger resistor will allow less current to pass..that is what we are looking for..the voltage across that is of lesser importance ..for example..if you put a 750R resistor and the voltage goes up to 12 volts the current will be 16mA..better..but still too high...if you have 750R resistor and voltage remains 6,5V...you're in ballpark country 8,7mA

I don't understand why so much current is drawn though???
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Old 16th April 2005, 08:36 PM   #14
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OK. Problem solved. Turned out my 220 cathode resistor was really 220K!! I apologize. But, in my defense, this was the one part I purchased at Rat Shack and the package did say 220 (I kept the packing). Someone must have re-stapled into the wrong package. Further, this was also the first time I used a digital multimeter and when I checked before installing and during troubleshooting, I never noticed the little "K" in the corner of the display. In fact, it was only when I pulled out my analog meter that I noticed something must be wrong as there was no reading in the "1X" range.

I appreciate everyone's help and promise to return the favor as best I can on my way up the learning curve.
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Old 16th April 2005, 08:41 PM   #15
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Great! Good the hear.

So the problem was the exact opposite..too little current

6,5V/220 000R = 0, 03mA
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