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  • #7347
    Cameron Burns
    Forum Participant

    I have been reading lately about radio power supplies and am hung up on something which i’m sure the rest of you can easily answer. It is regarding the rectifier (for example an 80) and the path that current takes. I’m not clear on the direction of current flow and the mixing of the ac in the filament circuit, and the ripple dc from the rectifier.

    Assuming a transformer, and the conduction of current from the filament to the plate when one plate is positive, here’s what i understand:

    the filament generates the electrons which will flow from filament to the positive plate. Then the current flows from the plate towards ground which would be the centre tap on the transformer? How does it get to the rest of the circuit–that is the B plus circuit? OR…does the current flow from ground centre tap through the positive plate and into the filament and Bplus circuit.

    Something tells me the answer is simple, but the light bulb just hasn’t gone on yet.

    #7410
    Steve Dow
    Forum Participant

    Following the flow of electrons, the starting point is when the center tap of the rectifier
    high voltage winding of the power transformer is negative, with respect to the end attached
    to one of the plates. That plate is now positive.

    That center tap is connected to ground in most radios. (chassis)

    Consider another tube, the output tube, for example a 6V6. Electrons flow from the ground
    up to the cathode of the 6V6, where they replenish, those produced by the hot surface.

    Those electrons flow up to the plate of the 6V6, on through the output transformer, back to
    hot filament of the 80 rectifier.

    Those electrons replenish those produced by hot surface of the 80 filament.

    The plate of the 80, now positive, pulls the electron back through the power transformer
    winding back to the starting place.

    Electrons are negative.

    Positive means there is a lack of electrons.

    #7418
    John Greenland
    CVRS Member

    Cameron;
    See if this article helps.

    https://www.americanradiohistory.com/Archive-Hands-On-Electronics/Hands-On-1984-Summer.pdf

    See page 53 of the pdf file, referenced above.

    Regards; John VO1-CAT

    #7478
    Cameron Burns
    Forum Participant

    Thanks for the links and info.

    c

    #7978
    Scott
    Forum Participant

    AC and DC power can flow or exist along the same path/wire, but only AC can pas through a capacitor. The coupling capacitors isolate the DC within the tube/valve while allowing the AC to pass/continue through the circuit.
    The filament does not emit electrons. It heats the cathode, which emits negatively charged electrons that are attracted to the B+ plate. The AC signal (from the radio tuning section of the circuit) enters the pre-amp tube via the grid. From the pre-amp tube B+, the AC radio signal passes through a coupling capacitor (which leaves the DC power behind inside the tube) and the AC goes to volume/tone controls. From there, the AC signal in a single ended circuit will go into the power output tube grid. If the circuit is push-pull (two output tubes), there will be a phase inverter tube between the pre-amp and power tubes.

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