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Old 03-16-2011, 10:27 PM
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old_tv_nut old_tv_nut is offline
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Join Date: Jul 2004
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It looks to me like the 220k resistor and 10k-47k are swapped. This is a touchy circuit configuration because the bias depends on the current gain ("beta") of the transistor. Since the base current is the collector current divided by beta, you want the resistor from base to collector to equal (very approximately) beta times the resistor in the collector. You have about 4.3 volts to work with once you discount the base-emitter voltage, and want half of this to appear across the collector resistor and half on the collector. So, I would try R2 = 10k and then play with R1, using maybe 100k for a starting value. The low value of collector voltage is to be expected with the values posted. You should be shooting for about (0.7 + (4.3)/2) = 2.85 volts on the collector to center the range.
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