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Ashdown Mag 200 bass amp

Discussion in 'Electronic Repair' started by N Cook, May 11, 2007.

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  1. N Cook

    N Cook Guest

    Blown illumination lamp behind the retro analogue VU meter and no other neon
    or LED to show the amp is on. It is marked R51 on the overlay and the
    schematic from Ashdown but no V or Watts. I will probably up the dropper and
    put a blue LED in there. Anyone happen to know what sort of rating and
    voltage it was ? Connected to full + to - 15 V dc , so 30V through a 1/3W,
    220 ohm dropper to this 1/2 inch long, 1/8 inch diameter wire ended bulb.
    Ohm's law fashion presumably about 30mA, 28 Volt. No chance it was a neon or
    phospher lamp ? as it is a frosted glass bulb, so cannot see the inside.

    While at it anyone know of a better way of mounting the VU meter so it does
    not push in if touched from the front.
  2. Arfa Daily

    Arfa Daily Guest

    Have not had to replace the lamp on one of these, so cannot offer any more
    than you have already worked out, except to say that they are a very
    innefficient company to get parts out of, and that one of the music store
    owners that I do work for, calls them " Trashdown " ...

    I currently have two of theirs in, one which requires an output tranny, and
    the other, a mains tranny. They have both sat here for 6 months now, waiting

  3. N Cook

    N Cook Guest

    This one was false protection cutting in, cured that.
    I don't know what the illuminated meter looked like as original but I reckon
    my re-jig would be better, looks quite nifty.
    Put a 2K , 3W dropper in and a bright blue LED wired-in and moved to
    vertically under the meter movement when mounted in chassis, so refraction ,
    through the plastic, forms a blue ring around the ali cut out , especially
    now I've abraided the aluminium in that recess, plus a bright spot under the
    meter that shows in bright ambient light and it also throws a light on the
    scale. 2 LEDs would have been better as the static part of the movement
    shadows part.
    Fitted a nylon bolt through the pcb to tighten up against the meter when its
    aligned into the chassis.
  4. N Cook

    N Cook Guest

    I had to replace one of the long shaft pots with a normal one with bush nut
    against the front panel. Instead of using the same normal shaft ones as the
    filter ones where the large area of mounting paxolin doess't matter as any
    strain is taken by the nuts. The long shaft ones just pass through a plastic
    sleeve in the front panel and any abuse gets passed to the paxolin to break
    easily. I would have used the normal ones throughout with bush nuts and
    extended the terminals by 1/2 inch to the pcb, rather than inherently weak
    unfixed pots with long shafts.

    My circular blue ring illuminator mod looked the bees' knees last night when
    I tried it in subdued light
  5. Arfa Daily

    Arfa Daily Guest

    I will bear that little 'mod' in mind in case I get one in the future. I see
    quite a lot of Trashdowns from this one particular shop, and know exactly
    the meter and lamp that you refer to, but as I say, I haven't come across an
    open one yet ...

  6. N Cook

    N Cook Guest

    I put a pic on here
    2 LEDs either side of the static part of the movement would have been
    better, more even - next time.
    I suppose some would say it destroys the retro look.
  7. Arfa Daily

    Arfa Daily Guest

    I always think that the 'retro' look on these is pretty pseudo anyway, so I
    don't think that what you've done detracts from the original at all.

  8. N Cook

    N Cook Guest

    Seeing the price of one BUZ900 or 906 of 13 to 18 GBP reminded me to start a
    thread for any generic (cheap) power FETs

    Back the Trashdown
    Because of the mm or so protrusion of the plastic bezel through the
    aluminium even seriously side on view is quite nifty.
  9. Arfa Daily

    Arfa Daily Guest

    It looks good in the photo. As far as subbing power MOSFETs goes, I've never
    been easy with doing that in the same way as it tends to be done with
    bipolars. I've always found mossies to be tricky little buggers, and have
    only ever replaced with genuine originals, no matter what the cost. There
    are so many different varieties, often having very tiny and subtle, but
    often very significant differences.

    As an example, I was working on a hybrid band amp a few weeks ago. It was
    actually a Traynor YCV40. It had two problems, one of which was that the HT
    standby switch for the output valves (tubes) didn't work. Investigation
    showed that this was not just a switch in the HT line. It was a double pole
    job, one side of which was connected to a bi-colour LED for indication of HT
    on / off, and the other side was connected to the gate circuit, via an opto,
    of a power MOSFET type IRF830. The FET was short, and there was no signs of
    any other problems, so I went ahead and replaced it with a similar one from
    the IRF series. I went through three different ones in the end, and finished
    up replacing the opto, and checking and rechecking every component in the
    gate control circuit - and there's a few - to no avail. I might add that I
    was doing this only because the owner needed it quickly for a gig. In all
    cases, the FET would not switch. When the front panel switch was set to
    'standby', the HT dropped only a few volts.

    Eventually, the owner had to have it back with only the main fault fixed so
    that he could at least use it that night, and I had him bring it back the
    next week, by which time I'd ordered in an IRF830. As soon as this (correct)
    device had been fitted, completely normal HT switching had been restored.

  10. Ron(UK)

    Ron(UK) Guest

    Out of interest, what was wrong with the amp originally, and how did you
    fix it?

  11. N Cook

    N Cook Guest

    for me in future , you and anyone else
  12. N Cook

    N Cook Guest

    The owner never had seen a light behind the meter, so no mains-on indicator,
    all the time he'd owned it.
  13. N Cook

    N Cook Guest

    from the owner, concerning the blue meter
    "looks amazing! thanks for doing that, it really makes it stand out, cheers"
  14. Arfa Daily

    Arfa Daily Guest

    Good final result all round then !

  15. N Cook

    N Cook Guest

    I've not had a play with white LEDs yet. Missed out on a few remnant stock
    of white LED christmas light strings after last christmas, someone got there
    before me in the shoddy goods store.
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