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Surface maount and valves/tubes.

Discussion in 'Electronic Repair' started by N_Cook, Jul 23, 2008.

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  1. N_Cook

    N_Cook Guest

    Just repaired a tube amp , problem unrelated to this.
    But it seemed odd to me to have valves , in inverted
    orientation , ie under a pcb with SM resistors on it.

    Anyone foresee temperature cycling problems/ dislodged SMD in the future
    with such arrangements.
     
  2. Dave

    Dave Guest

    As they say "If it can be done, some fool will do it". Given that heat
    rises, I see no benefit whatsoever to putting a tube which converts 70% of
    the electricity fed through it to heat underneath a PCB. All it's going to
    do is shorten the life of the PCB components and, quite possibly, the tube.
    There's a reason why most tube amps have the tubes exposed or covered only
    by a mesh grille...

    just my 2 cents.
     
  3. boardjunkie

    boardjunkie Guest

    What the hell kind of amp was it??? Just so I can refuse repairs on
    that kind of garbage.....
     
  4. N_Cook

    N_Cook Guest

    onhttp://home.graffiti.net/diverse:graffiti.net/

    What the hell kind of amp was it??? Just so I can refuse repairs on
    that kind of garbage.....



    Laney LC15 from 2002
     
  5. Arfa Daily

    Arfa Daily Guest

    Well, I think maybe you've answered your own question there. If it has done
    six years so far without a problem of the type you are envisaging, I doubt
    that it's going to develop one. Those sm resistors are subjected to a lot of
    heat and various levels of thermal cycling when they are first fitted,
    that's a lot more intense than anything that the valves are going to
    generate in normal service. Many amps that I work on, have the output valves
    fitted upside down in a pcb-mounted holder, and it doesn't seem to cause a
    problem with either the service life of the valves, or the pcb above them. I
    have, however, had bad joints on the output valve holders of several Fenders
    recently, that have been manufactured with lead-free solder. I don't know if
    this is as a result of thermal cycling or not, but I rather suspect that it
    is a 'normal' lead-free production problem that we are getting used to
    seeing on all sorts of equipment, now.

    Arfa
     
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