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Thread: Question about 7591 tubes

  1. #1
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    Question about 7591 tubes

    This drawing looks like I make the 348v grid connection at both pins 4 & 8. Can anyone shed some wisdom on me about what's going on there? Tube data shows they are both G2, why not be able to connect to only one of the pins?

    ~Semi-No0b Hobbyist~

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    The screen pins should be tied together for "efficient operation of the screen". (from the data sheet/ last page)

    7591.pdf
    Justin Thomas and mort like this.

  3. #3
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    And, Ampeg did exactly that. They're the most frequent guitar-amp user of those tubes. Of course, for "inefficient" screen operation... doesn't say anything will explode now, does it?

    Justin
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  4. #4
    Senior Member mhuss's Avatar
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    I wouldn't be surprised if the two pins were connected to each end of the screen grid (in fact, that's how it's drawn in the RCA manual page). In that case, connecting both == minimum impedance, best result, but either end would still work.

  5. #5
    Supporting Member loudthud's Avatar
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    Often times the internal structure of a tube dictates the pin connections. In this case note that pins 4 and 8 are located directly opposite each other. The screen grid consists of a pair of vertical rods that go through the bottom mica disc, straight through the glass and into the base without any bends. A spiral wire between the vertical rods forms the screen grid. This may be the only support for the internal structure of the tube while it is being assembled.
    sgelectric likes this.
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personel.

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