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Ok I know this is a pretty narrow question. I'm learning about vaccum tubes, and I think I have the basics down, but this particular setup is confusing me. See the attached picture.

enter image description here

In the given picture, we can see that the negative rectified output line connects to both the main secondary winding and the low voltage winding for the cathode heating. Why?

Unless I misunderstand something, the cathode heater is a complete circuit. Why does the rectified output need to connect back to the center-tap of the low-voltage winding?

Thanks in advance.

ibanix
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3 Answers3

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Because if the heater isn't earthed to a common ground, it will accumulate static charge, the field of which will bias the plate, causing the rectifier to not work correctly, and causing emitter-heater leakage.

david
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It is acting like a diode, the filament is the cathode connection. This was common in the previous vacuum tube erera, it saved a pin. Careful if you build it, they can give you a nasty shock. the center tap evens the ware on the filament and helps reduce hum.

Gil
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    According to a GE datasheet, the 6W6GT IS a diode. In that circuit, the cathode is the positive output. The filament is insulated from the cathode. – Peter Bennett Oct 27 '21 at 01:25
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The 6w4GT tube is a direct heated dual triode. That thing connected to DC output plus is the control grid. The cathode and the filament are the same thing.

Janka
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