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Model 650 Cap 77, 10mfd, Polarity Question - Printable Version

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Model 650 Cap 77, 10mfd, Polarity Question - Sourbone - 03-21-2016

Hello:

I've nearly finisher recapping a model 650. Ecap number 77 is dual. The 10mfd section is connected to the transformer center tap and ground. I'm wondering about the polarity. Should the positive end of the 10mfd cap connect to the center tap and the negative end connect to ground? 

RE: Model 650 Cap 77, 10mfd, Polarity Question - KCMike - 03-21-2016

The center tap being the most negative point the chassis is more positive. I would connect the + to chassis.

RE: Model 650 Cap 77, 10mfd, Polarity Question - Mondial - 03-21-2016

The positive terminal should connect to chassis ground, and the negative to the center tap. 

The center tap is the most negative voltage  point in the circuit, so the negative terminal of the cap connects there. 

RE: Model 650 Cap 77, 10mfd, Polarity Question - morzh - 03-21-2016

Yes this is one of those questions asked about few hundred times here.
The connection is counter-intuitive, as people are accustomed to seeing GND being the most negative point and so caps' minusses going to it.

In this case which is present in many radios, the centertap is the most negative point in the whole of the schematic; everything else relative to it is positive.

Hence the capacitor's minus goes to the centertap, and the plus goes to the Ground (chassis).

RE: Model 650 Cap 77, 10mfd, Polarity Question - Sourbone - 03-21-2016

Thanks for your help and expertise.

Dave

RE: Model 650 Cap 77, 10mfd, Polarity Question - AI2V - 03-22-2016

That's the negative supply that offers negative voltages to grids (mostly) throughout the radio. It's a common circuit in most radios, primarily the better ones.  You don't need a high voltage cap in these circuits and 50 volts is very safe. As in the other posts, this cap has a positive connected to ground.