Help understanding a darlington pair

Buckeye Sound · 28th August 2007, 05:46 PM

I'm primarily a tube guy, so I need some help sorting this out. I'm getting negative voltage where I believe it should positive and I'm not sure why. I'm getting (-) between R 27, R26, and C16. I believe it should be positive? Am I correct? I suspect that R27 is breaking down allowing the (-) when it shouldn't be. Any thoughts on this?

Thanks

I've attached a section of the schematic. Thanks.

acid_k2 · 28th August 2007, 06:14 PM

why do you believe it should be positive?

consider resistors r26-r27.... at the base of Q1 you should obtain about -11V.... (without considering base current of Q1)

jerluwoo · 28th August 2007, 08:09 PM

Yes it should be negative voltage there and the point where q1 and q2's collectors and c18 connect should be near 0 volts.

longthrow · 28th August 2007, 11:25 PM

considering the voltage divider resistors alone(r26 & 27), you'll definitely obtain a negative voltage since r27 is much lower than r26..

Buckeye Sound · 28th August 2007, 11:56 PM

Thanks. I discovered a bad joint, and now I can see how it is supposed to work, and it does with neg voltage and nominal voltage at the collectors. (Still not sure if I like these things!)Thanks again for the help.

28th August 2007, 11:25 PM	#4
longthrow diyAudio Member Join Date: Aug 2007 Location: cebu phils	considering the voltage divider resistors alone(r26 & 27), you'll definitely obtain a negative voltage since r27 is much lower than r26.. __________________ H V E Audio

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28th August 2007, 06:14 PM	#2
acid_k2 diyAudio Member Join Date: Oct 2006	why do you believe it should be positive? consider resistors r26-r27.... at the base of Q1 you should obtain about -11V.... (without considering base current of Q1)

28th August 2007, 08:09 PM	#3
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	Yes it should be negative voltage there and the point where q1 and q2's collectors and c18 connect should be near 0 volts.

28th August 2007, 11:56 PM	#5
Buckeye Sound diyAudio Member Join Date: Jun 2005 Location: Here	Thanks. I discovered a bad joint, and now I can see how it is supposed to work, and it does with neg voltage and nominal voltage at the collectors. (Still not sure if I like these things!)Thanks again for the help.

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