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Valve/tube screening can problem

Discussion in 'Electronic Repair' started by N_Cook, Mar 18, 2009.

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  1. N_Cook

    N_Cook Guest

    Mesa Nomad 55 with one of the 12AX7 snow capped and a neat ring around the
    top of the glass envelope. Obviously due to the bed-spring gauge of spring
    inside the can. 2Kg to halve the spring length, probably 2/3 compression in
    No point in replacing without changing all the springs or something. How to
    reform a weak straight compression spring (easily available) to conical or
    otherwise fit inside the can and the glass touching end be centrally
    posistioned. ?
    Secondly there is no dedent to stop the cans rotating other than use of
    heavy springs - catch 22. What to do, retrofit, without taking the amp apart
    to get to the inside of the chassis. So far I've discovered a working , but
    not elegant solution. One of those brass-eyelet hand pincer/dies pushing the
    die pin outwards to deform a pip in the aluminium, outwards, 1/4 way round
    so it locates in one of the 2 chassis cutaways. Needs some rubber padding on
    the outside so the other anvil half does not excessively damage that local
    area. Any other solutions anyone else has found, particularly forming or
    re-forming spring metal to something like conical My attempts are very
  2. N_Cook

    N_Cook Guest

    This is a work-around for the springs. May have gone too far the other way
    200gm rather than 2Kg. Expanded aluminium mesh (for continued ventillation
    through the central hole in the can) cut to a square to squash inside the
    can. Straught 12mm diameter compression spring. One end , the last 2mm ,
    bend to point axially. Thread that end through a suitable hole inthe mesh
    and push around for a near circle and feed back through the mesh with the
    return poking through the adjascent hole. Curl back the corners of the mesh
    enough to push into the can. Use a din connector cover to go over the spring
    and push the mesh into the can. Then with din cover in place , use a
    screwdriver to push the mesh down to wedge into the can top. The spring then
    stays centrally and axially located .

    The eyelet pliers fudge works quite well for dedenting the cans, combined
    with the existing "O" ring antivibration ring.

    rarp added as probably relevant
  3. Kirk Johnson

    Kirk Johnson Guest

    Maybe give this a try lad

    Always works wonders for me!

    Kirk Johnson
    "EXTREME Stretching Specialist"
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