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Strange filament behavour

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Joel

Joel

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Joined 2002
joeltunnah.com
...The filament in a DHT, since it is the cathode, cannot be isolated. It must be referenced to B-, C+, and possibly chassis "ground" if it's the same as the other two.
Click to expand...

Ralph said:
I don't understand this.
Click to expand...

Ralph,
The "plate circuit" is cathode->Plate->PSU->cathode, etc. If the cathode is not connected in any way to the bottom of the power supply, no current can flow through the tube. In a "directly heated" tube, there is no seperate cathode - it is the filament. So, you can see how we can't isolate the filament from the rest of the circuit. Make sense?
This is not relevant to your idea of lifting the heaters +40V above ground though.
 
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