Directly Heat Triode Filament Supply Issues

In a DHT the cathode is also the filament so both heating current and signal voltages are present. Common perceptions : AC=good but noisy, DC=quiet but cold sounding and has glare

What is needed :

    1. low noise heating current (ie low ripple and no high frequency hash)
    2. no intermodulation between signal and heating current
    3. no audio signal loss through heating current device

1. Cathode bias: When applied to the cathode, it becomes self biasing, and the Anode voltage needs to be increased by the amount of voltage drop across the cathode resistor. So cathode bias circuits generally require a higher anode voltage to achieve the same power output.
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