Center shields and internal shields

Discussion in 'Shock Brother's DIY Amps' started by separateness, May 15, 2021.

  1. separateness

    separateness TDPRI Member

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    I have two vaguely related questions which I feel might be answered here. I am working on a low voltage mic preamp thing using 6GM8 tubes. As you may know, these have 6.3V only heaters which are tied to pins 4 and 5. Tied to pin 9 is an internal shield which protects the two triode stages from one another. Having done some research it seems that this shield is mostly of use in HF applications. In the few 6GM8 amplifier schematics I've seen these are usually tied to ground through a capacitor. Is it even necessary to ground the internal shield at all for audio frequency applications? If so does it have to be through a capacitor, or can they be DC coupled to ground? If a capacitor is necessary or advisable, how does one determine or calculate the proper value?

    Vaguely related is this question: The tube sockets I bought for this project off of AES are ceramic type (because they looked so nice) with a 'center shield'. I have never seen sockets such as this, what is this center shield used for? Surely it is irrelevant in my use case but I cannot think of a purpose for these things and it is bothering me.

    Thank you.
     
  2. printer2

    printer2 Poster Extraordinaire

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    The shield can be tied directly to ground. It probably will not do much for shielding noise though. The center post in a socket was used as an extra tie point when using point-to-point construction. Some sockets came with four lugs on the metal mounting ring to give a ground path to parts tied to the tube pins.
     
    sds1 likes this.
  3. separateness

    separateness TDPRI Member

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    Excellent. Thank you so much.
     
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