Aristo cold head

Discussion in 'Darkroom Developing and Printing' started by john, May 17, 2008.

  1. john

    john Guest

    I know nothing about cold heads (except being bald in a Minnesota Winter).

    Need something for the 8x10 Saltzman enlarger. On EvilBay there is an Aristo
    T12.

    Seller wants $575 BIN. Here is the ad copy:

    "This is the top-of-the-line 8x10 enlarger light source. Aristo T12 High
    Intensity Light Head is a two part unit -lamp housing and power pack- which
    contains a three prong thermo cord which operates the thermostatically
    controlled heater. This is plugged into any available 115V outlet. The lamp
    housing is 11-7/8" x 11-7/8" x 6-3/4" high."

    Is that everything I need for the light source? Is there a particular
    "gotcha" to beware of?

    I truly appreciate any help on this you all can offer.

    John
     
    john, May 17, 2008
    #1
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  2. Hi John,

    I don't have any personal experience with an Aristo T12, but perhaps Aristo's
    own product page for this unit will help you in determining if this unit is
    right for you...

    http://www.aristogrid.com/t12.htm

    Ken
     
    Ken Nadvornick, May 17, 2008
    #2
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  3. john

    john Guest

    OMG! I broke my own rule! I did not look it up. See, I thought it was an
    obsolete part.
    Thanks for the nudge, Ken!

    John
     
    john, May 17, 2008
    #3
  4. Aristo make a lot of different color tubes in their heads, each with a
    different characteristic curve. Some will work pretty well with about Y40 or
    so yellow filter in addition to your regular vc filters. Others will not.

    You might find the following curves helpful:

    http://www.aristogrid.com/spd.htm

    They also make heads with a blue and a green tube so you can use VC paper
    more easily. I have an Aristo head (D2HI) that came with either a W45 or a
    V54 tube in it and that worked OK with a yellow filter, although I used
    graded paper at the time, so it did not matter much to me.
     
    Jean-David Beyer, May 17, 2008
    #4
  5. john

    john Guest

    That is a critical issue. Thank you! Aristo also has a device to allow the
    use of digital timers. Is it necessary with the F-Stop timer?
     
    john, May 17, 2008
    #5
  6. You may need to stick to graded paper - it looks like the
    original 'actinic' tube. I had a head with this tube on
    a D-series Omega and it only wanted to produce grade 4+
    VC prints. Some people say they can get by throwing
    a lot of yellow filtration into the system.
     
    Nicholas O. Lindan, May 17, 2008
    #6
  7. It shouldn't be.

    There are two technologies timers use to control
    the lamp: electro-mechanical relays and solid-state
    silicon controlled rectifiers (SCRs).

    Some electronic timers with relays get upset by the
    electrical interference generated when the contacts
    open with an inductive load. Current through an
    inductor wants to keep flowing and can't be stopped
    instantly. When relay contacts open the current
    creates a small arc across the contacts. A 'snubber
    circuit' across the contacts provides a path for this
    current and limits the arc. The f-Stop Timer uses
    a snubbed relay rated at 12 amps.

    Since SCRs only turn off when the current goes
    to zero they have no trouble turning off inductive
    loads. OTOH, they can have problems with incandescent
    lamps. When a light bulb fails it often creates
    a dead short - the bright flash/pop - and the current
    through the short can destroy an SCR that is not
    adequately protected. They are also prey to
    high-voltage surges on the power lines. Snubber
    circuits are used with SCR's, but this time to
    absorb power line spikes when the SCR is off.

    Timers that are properly designed and used will
    work without problems using either relays or
    SCRs.

    High-power loads connected to a timer can require
    an external contactor to handle the current. Regular
    Aristo 4x5 heads are no problem for most any timer,
    including the Darkroom Automation f-Stop Timer.

    I don't know the inductive characteristics of the T-12
    and don't have any experience with this unit. My guess
    is it will work, but there is a chance the external
    'solid state contactor' may be needed. In any case,
    plugging the head in and seeing if it works will cause
    no damage to the timer.
     
    Nicholas O. Lindan, May 17, 2008
    #7
  8. john

    john Guest

    Very good to know. Thank you.

    So now I know the light source is clearly feasible. I just have to rip this
    check out of my tight fist and do it.
     
    john, May 17, 2008
    #8
  9. Others have answered your questions but contratulations
    on having this monster, an absolutely superb chunk of
    machinery.
    If you have the original shutter it will work well with
    the cold light head, they want to run continuously. The
    Arista has a heater in it to make the output more uniform
    when its used intermittantly but all gaseous discharge lamps
    increase output as they get hotter and most like to work on
    a continuous basis. The Saltzman shutter was made to work
    with the original mercury vapour lamp house which _had_ to
    run continuously. Saltzman had other lamphouses available
    but the Cooper-Hewitt tube type was the most common.
    Arista makes lamps which are compatible with variable
    contrast paper and can be refitted to older lamphouses.
    Does your Saltzman have one or two support rods for the
    bellows?
     
    Richard Knoppow, May 17, 2008
    #9
  10. john

    john Guest

    (re: saltsman enlarger, Aristo T12 cold head)
    No shutter came with it, but I have a 110V shutter from old long-roll school
    camera that will fit in front of either lens.
    It has two, Richard, with the worm-drive rod between them, driven by a
    sintered bronze gear. I can make pictures to put online if you wish.

    John
     
    john, May 17, 2008
    #10
  11. I do not know the inductive characteristics of cold light heads either.
    If the load on the step up transformer were resistive, the load would be
    reflected back through the transformer and place a resistive load on the
    timer and the power company. Now a gas discharge tube is not resistive, but
    it probably has a resistor in series with it to reduce the peak current
    through the tube, so it may be more resistive than the tube itself.
     
    Jean-David Beyer, May 18, 2008
    #11
  12. You have the more elabrorate version of the enlarger.
    The cheaper (but not cheap) one had the single support rod.
    This type was also used for aerial mapping and similar
    applicatons. It should have a focusing wheel to drive the
    bellows. Some of the larger models also had a small
    handwheel to operate the stop ring on the lens.
    Photographs would be interesting, I suspect many have
    never seen a Saltzman. I have an ancient Saltzman catalogue
    somewhere. I really must search it out.
     
    Richard Knoppow, May 18, 2008
    #12
  13. john

    john Guest

    This one has two hand-wheels below the baseboard. One raises and lowers the
    head assembly using two chains that run up and down the inside of the main
    column, and the other wheel moves the bellows (focus). It has another pair
    of smaller hand-wheels on the horizontal supports (of the triangulated head
    support) to move the head to and fro. Today I am measuring those parts to
    see if I can add a belt or lightweight chain drive from one of the smaller
    wheels to drive the other: this would allow the operator to move to-fro
    using one wheel and obviate having the enlarger sit 30 inches from the wall.
    (Or a person could just disengage the worm-screw and push/pull by hand.)

    I would very much like to work out a remove F-stop control. Will think about
    it.

    There are mounts for other things such as the red filter rod which are empty
    right now. And an odd part that I cannot figure out. If I can get a digital
    snapshooter I will make some pictures and post the address.
     
    john, May 18, 2008
    #13
  14. A gas discharge tube has a negative resistance: If you increase
    the current it will lower the tube voltage. Modeling the lamp
    as a constant voltage, though, is good enough for most circuit
    analysis - the result is like driving current backwards through
    a battery, the voltage on the 'battery' is the arc voltage.
    In this model the lamp has zero resistance.

    Since the lamp is pretty much a short circuit - zero resistance
    - there needs to be a 'ballast' in series with the lamp. The
    ballast can be a resistor, capacitor or inductor. The ballast
    impedance (the general term for something that opposes current)
    controls the lamp current.

    In almost all equipment the ballast is either inductive or
    capacitive - called a reactive ballast. Resistor ballasts are
    sometimes found in very old equipment.

    A reactive ballast will draw current 90 degrees out of phase
    with the power line. The power that it blocks is stored in
    either a magnetic field (inductor) or an electric field (capacitor)
    and given back to the power line in the next half cycle (a sloppy
    explanation, but probably good enough). A resistive ballast
    dissipates the power as heat and the power is gone forever.

    The reactive ballast causes the system to draw extra current,
    though not power. This upsets the power company, means larger
    wiring and transformers are needed and raises the electric bill
    if your meter charges you for VARs. Large lamp power supplies
    include power-factor correction by adding compensating inductance
    to a capacitive ballast power supply or compensating capacitance to
    an inductive ballast power supply. This makes the lamp system
    draw the least amount of current and look like a resistor to the
    power line. http://en.wikipedia.org/wiki/Power_factor

    Putting a capacitor of the right value at the input to an Aristo
    lamp will make the system look like a regular old light bulb and
    there will be no inductive kick when it is turned off. However,
    because of the capacitor there will now be a current surge when the
    lamp is turned on. "Pay now or pay later."

    These problems can be eliminated by connecting the power when the
    AC voltage is zero and disconnecting the power when the AC current
    is zero. This is what Aristo's 'solid state contactor' achieves.
     
    Nicholas O. Lindan, May 18, 2008
    #14
  15. The filter rod was also used to hold the shutter. The
    original was a two blade arrangement similar to a Packard
    shutter worked by a foot pedal. Not all had the iris control
    and I don't know the details of how it was coupled.
    One option was a condenser lamphouse with about 14"
    condensers and a mirror arrangment for the lamp. These had a
    focusing control for the lamp on the housing and its
    possible some had a remote handwheel for this also. I wish I
    could find my catalogue but it got boxed up. Time for some
    garage cleaning I'm afraid.
    You probably need a five foot ladder to go along with
    the enlarger.
    Saltzman also made a very heavy, geared, tilting
    baseboard for perspective correction. I've only seen
    pictures of these.
     
    Richard Knoppow, May 18, 2008
    #15
  16. john

    john Guest

    This one has provisions for two rods, each about 1" from the edge of the
    lens, extending down as far as one wants to make a rod. I'm a little
    concerned that shutter movement will cause vibration shake, however subtle,
    so I might mount the shutter from a sliding arrangement on the mail column,
    which just cannot possibly move. (750 pounds of it). Two more rods can be
    added with simple drilling and tapping. So much real-estate on this thing!
    Heh! I have a vision of Watson on the ladder, "Mr. Holmes, is it correct
    now, Sir?"
    Over the years of building things like Harleys
    http://www.digoliardi.net/butcher.jpg , working on tractors, building cars
    and rebuilding VWs http://www.digoliardi.net/58.jpg ,
    http://www.digoliardi.net/bug_n_brad.jpg has made me comfortable with making
    large things. A geared baseboard would be simple. But the demand for such a
    thing is a market of One!
     
    john, May 18, 2008
    #16
  17. john

    john Guest

    Richard, here a just a couple snapshots of two parts of the Saltzman. The
    upper section of the snapshot shows the front lower with the large two
    hand-wheels. Left is focus and right raises and lowers the whole head.

    The close-up is the rear of one horizontal bar of the head section. Turning
    the wheel moves the head forward and back. The other is exactly the same.
    They were missing the gears, retainers, and spacers - everything but the
    wheels. I haven't got the connecting chain yet (#40 chain, I think
    ten-pitch). Got the hubs, spacers and gears at the tractor parts shop today.

    It's hard to shoot snapshots in the shed. This was done with the doors open
    to the 6pm MinneSnowta May sun.
     
    john, May 19, 2008
    #17
  18. john

    john Guest

    john, May 19, 2008
    #18
  19. OMG, I'm drooling; a real piece of Industrial Equipment. Should be a
    centerfold in some magazine. Great stuff!

    Good luck, and please keep us informed of future developments.
     
    David Nebenzahl, May 19, 2008
    #19
  20. john

    john Guest

    One of my brothers, an expert in ancient warfare, alikened it to a seige
    machine. So if it doesn't work out...
     
    john, May 19, 2008
    #20
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