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 Post subject: Why a grounded center tap on the 6.3 winding?
PostPosted: Jan Thu 23, 2020 4:13 am 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Why a grounded center tap on the 6.3 v winding? Does this have a hum-bucking effect?

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 Post subject: Re: Why a grounded center tap on the 6.3 winding?
PostPosted: Jan Thu 23, 2020 4:20 am 
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Location: near ST Louis Mo 62002
It lowers the impeadance to and voltage to ground of the filaments of the tubes and does help minimize the hum .

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 Post subject: Re: Why a grounded center tap on the 6.3 winding?
PostPosted: Jan Fri 24, 2020 4:32 am 
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Thanks, Mark.

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 Post subject: Re: Why a grounded center tap on the 6.3 winding?
PostPosted: Jan Sat 25, 2020 10:28 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Rochester NY USA
Remember: the components that give you trouble aren't always on the schematic...

There is capacitance between the primary and secondary of the transformer - high impedance at line frequency but lower as frequency increases. And this provides a path into your circuit unless one side or the center-tap is grounded. The tube's heater isn't directly connected to anywhere else, but heater wire could couple that noise into other circuits. And by grounding the center-tap of a 6V winding, the heater wires have only 3V each, of opposite phase. So the net 60 Hz electric field cancels. Twist the wires and magnetic fields cancel too. When signals are small, all noise sources have to be kept even smaller!

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 Post subject: Re: Why a grounded center tap on the 6.3 winding?
PostPosted: Jan Sat 25, 2020 11:52 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
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Location: Vancouver Island, Canada
Makes sense, two equal circuits of half the voltage in opposite phase.

Tom, thanks again for the output transformer you found for me last year, is working great and looks like the original. Your Stromberg to my Marconi. 8)

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