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    Grid and Plate wire routing

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    heyraz

    Posts : 58
    Join date : 2011-10-26

    Grid and Plate wire routing

    Post by heyraz on Tue Jan 10, 2012 2:36 pm

    The stock ST-70 has a grid and plate wire twisted together between each valve and its output transformer (Blue and Green then Blue/White and Green/White). What is the rationale for this? Don't they carry different voltages and if so wouldn't any cancellation of hum would be unequal? Wouldn't the wire with the higher voltage induce a current into the lower voltage wire?
    I am building an amp from scratch with the pentode/triode switches and think it would be better to twist the grid wires (Green and Green/White) together and the same for the plate wires (Blue and Blue/White). After the twisted pairs are routed to a point between the valves they can be separated and connected accordingly. Am I wrong?

    Bob Latino
    Admin

    Posts : 2377
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Grid and Plate wire routing

    Post by Bob Latino on Tue Jan 10, 2012 3:12 pm

    Twisting these wires is not really necessary from a hum/noise point of view because these wires carry DC voltages not AC voltages. Twisting the wires does make for a neater appearance though on any ST-70 with no triode/ultralinear switches. Wires that carry AC voltages like the tube heaters should be twisted to cancel out any hum.

    Do they carry different voltages? Not really. The green and green/white wires (ultralinear screen taps or grids) may be 1 or 2 volts higher in voltage than the plates. (blue and blue/white wires). The voltage gradient is so low that virtually no voltage will be induced. You can just use single runs (untwisted) of wire to connect up your triode/ultralinear switches.

    Bob

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Grid and Plate wire routing

    Post by heyraz on Tue Jan 10, 2012 7:23 pm

    Thanks for clearing that up. Rich

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