triode heater ground question

gary h · 8th August 2009, 04:56 AM

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?

thanks,

gary

Hearinspace · 8th August 2009, 06:18 AM

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.

gary h · 8th August 2009, 06:26 AM

thanks,

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

g

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8th August 2009, 06:18 AM	#2
Hearinspace diyAudio Member 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.

8th August 2009, 06:26 AM	#3
gary h diyAudio Member Join Date: Apr 2006 Location: usa	thanks, of course, and it gives the series/parallel voltages right on the spec sheet. g