AC fils aren't going to add "hiss" anyway. Did you mean hum?
Two wotrhwhile tweaks, esp for DHTs, but can be of worthwhile benefit for indirectly heated tubes, are common mode chokes (about $3 ea, bigger values are better) and a cap across the fil pins on the socket of a couple of uF. Make sure it has good high frequency performance.
Two wotrhwhile tweaks, esp for DHTs, but can be of worthwhile benefit for indirectly heated tubes, are common mode chokes (about $3 ea, bigger values are better) and a cap across the fil pins on the socket of a couple of uF. Make sure it has good high frequency performance.
hum
If you're using indirectly heated tubes, designed for AC filament service, then merely grounding the center tap of the filament winding, and twisting the filament wires tightly together should fix any hum issues. Also, make sure they lay flat against the chassis.
In certain cases, you may have to add a potentiometer of low value (100 ohms) across the winding, with the wiper to ground.
I've never had a heater hum problem not be cured by the above methods.
If you're using indirectly heated tubes, designed for AC filament service, then merely grounding the center tap of the filament winding, and twisting the filament wires tightly together should fix any hum issues. Also, make sure they lay flat against the chassis.
In certain cases, you may have to add a potentiometer of low value (100 ohms) across the winding, with the wiper to ground.
I've never had a heater hum problem not be cured by the above methods.
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