• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

triode heater ground question

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gary h

Member
Joined 2006
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
 

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H

Hearinspace

Member
Joined 2008
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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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