microphonic tubes

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by canucklehead, Sep 10, 2019.

  1. canucklehead

    canucklehead Member

    Messages:
    84
    Joined:
    Aug 2, 2010
    Location:
    Vancouver Is, British Columbia
    I unfortunately discovered some 12AX7 and 5751 tubes my NOS and ANOS stash are microphonic. Instead of tossing them, can they still be used in the V3 or V4 positions of my 65 PRRI?
    cheers
    i
     
  2. pdf64

    pdf64 Member

    Messages:
    5,783
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    Yes, just fine, though if they are super microphonic then perhaps V4 only, but a 5751 may not have enough gain for reliable trem operation there.
    Also tubes that are microphonic in a combo may be fine for any suitable position in a head.
    All tubes are microphonic to some degree, whether it’s a problem depends on the application. The least tolerant application being the input stage of a combo, especially a higher gain one.
     
    Last edited: Sep 10, 2019
    Timbre Wolf likes this.
  3. canucklehead

    canucklehead Member

    Messages:
    84
    Joined:
    Aug 2, 2010
    Location:
    Vancouver Is, British Columbia
    Thanx for the response, pdf64. Why if tubes are microphonic in a combo, are they fine in any position in a head? What's the difference"
    cheers
    i
     
  4. HotBluePlates

    HotBluePlates Member

    Messages:
    6,018
    Joined:
    Mar 27, 2017
    You breezed right past the words that qualified his statement: "may" and "suitable position."

    First off, a head is sitting in a separate cabinet from the speakers. The speaker cab probably doesn't transmit all the vibration to its top surface, and the feet on the head cab may absorb what vibration gets to the top. And the head's cab may not transmit all the vibration from the feet, through the cab, to the chassis, to the sockets & tubes.

    Any microphonic tube is more problematic closer to the input jack. That's because everything that follows it amplifies any ringing/howling. So putting the microphonic tube late in the circuit (phase inverter, perhaps) is less likely to be troublesome.

    A lower gain head is less likely to go crazy from a microphonic tube than a high gain head. Or if there's a separate, low-gain channel the tube might do okay there.

    Sometimes you just have to try & see.
     
  5. canucklehead

    canucklehead Member

    Messages:
    84
    Joined:
    Aug 2, 2010
    Location:
    Vancouver Is, British Columbia

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice