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Old 8th August 2009, 04:56 AM   #1
gary h is offline gary h  United States
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Join Date: Apr 2006
Location: bay area, california
Default triode heater ground question

Hi all,

in the schematic below, I assume I can leave the 12au7 heater ground pin (9) unattached.

Am I wrong? Is there a better way?


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Old 8th August 2009, 06:18 AM   #2
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Join Date: Jun 2008
Pin 9 is the heater centre tap . If pin 9 is unused the power supply has to heat the entire series length of the heater which properly takes 12.6 volts. By (electrically) folding the heater filament "in two" or back on itself you heat the two halves in parallel requiring half the voltage (6.3) but twice the current.

So connect one end of the the 6.3 Volt secondary to both pins 4&5 together, and the other end to pin 9.
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Old 8th August 2009, 06:26 AM   #3
gary h is offline gary h  United States
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Join Date: Apr 2006
Location: bay area, california

of course, and it gives the series/parallel voltages right on the spec sheet.

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