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  • #13897
    Les Dickson
    CVRS Member

    I can’t figure out what purpose the potentiometer identified by the larger red arrow on this attached schematic. There is already a pot that modifies the tone, located by the output transformer. The pot in question fades to nothing because there is a problem in the circuitry between the IF amp (tube 58) and the 2nd detector (tube 227A) which is right where the pot sits.
    Any suggestions are very welcome.

    #13903
    Alistair Thomson
    Forum Participant

    Dan in Calgary worked on the York/Mayfair, so watch this space! 🙂 My guess is it has something to do with varying the DC voltage on the second detector plate, but I don’t know why.

    #13999
    Don McFarlane
    Forum Participant

    The “2nd Detector” 227A triode is being used as a diode, with the plate shorted to the grid. The potentiometer in question would adjust the DC plate bias current. I don’t have any data on this tube type, but I suspect it would be nonlinear, and the pot would adjust it to the most nonlinear spot, maximizing the detected audio signal. To adjust it properly, I would use an amplitude modulated signal from a generator, and adjust the pot for the maximum audio output.

    #14121
    Gordon Dann
    CVRS Member

    the 1/2 meg is a vol pot the 50k is the tone pot

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