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  1. #101
    Nicholas Lindan's Avatar
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    From what I can tell from looking at the pictures:

    The flash discharge isn't made using the electrolytic capacitors - they are used simply for supplying DC voltage to the charging circuit. HV can electrolytics have a very long life. I wouldn't bother changing them. The electrolytic problem was with cheaply made low to medium voltage electrolytics from the far east. Any electrolytic can fail, as can any other electronic component, but wholesale replacement is only warranted with equipment with small 'shrink wrapped' PC mounted electrolytics.

    The oil filled capacitor - big square gray painted can mounted on the top of the chassis - is the flash capacitor. It does not need to be replaced - it doesn't wear out.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  2. #102
    Bill Burk's Avatar
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    Michael R 1974,

    You won't have problems with old capacitors unless you decide to build something with old flashes like Vivitar 283. There might be opinions whether Tungsten or Daylight is appropriate, but no lamp is perfect - and although the sun has the perfect spectrum to match sunlight, it isn't considered a good sensitometric light source. One reason is you can't count on its brightness. So I think filtered Tungsten is a fair compromise good enough for development time control.

    The reason my system is under scrutiny is that I'm trying to estimate its absolute light output... and find out why my estimate is so far from documentation.

    Under the top hood there is date stamped: Oct 26 1988. Serial is 1406.

    The two aluminum cans are Sprague 29D13 250 uf 475 v. They do get connected to the lamp for 10^-2 and 10^-3. As I understand flash, the tube has high resistance until the gas is ionized by the ignition coil. So it is normal to hot wire the lamp to the capacitors.

    All the resistors are gold (5% tolerance), and "binning" (measuring the actual capacitance and sorting them into bins) could have brought two capacitors in series to within 5% tolerance.

    I quoted the resistances from the color codes. R4 has an extra yellow mark, I think that gives it a high temperature rating. It measures 76K though it is coded 150K. Maybe this is bleeding more to ground than it should, or maybe there is a path with less resistance back through the capacitor. I didn't pull the part to measure it. R1-3 measure same as rated. R5-7 appear to be part of the 10^-4 circuit.

  3. #103
    ic-racer's Avatar
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    Quote Originally Posted by Bill Burk View Post
    Maybe this is bleeding more to ground than it should, or maybe there is a path with less resistance back through the capacitor.
    Of course DC resistance through the capacitor will be infinite unless it has an internal short. I hope it is just an error from in situ measurement. I hope the ohmmeter battery is slowly charging the capacitor and giving the wrong resistance measurement across the resistor rather than a bad capacitor.

    Bill, if I can paraphrase your earlier post for clarity, you feel 10-2 setting gives 178 mcs based on your film tests, while Steve's unit measured 765 mcs on that same setting, right? (Nominal for that setting is 800 mcs)

    And, you don't know if the other settings are low also, right?
    Last edited by ic-racer; 07-16-2012 at 12:11 PM. Click to view previous post history.

  4. #104
    Leigh B's Avatar
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    Quote Originally Posted by Bill Burk View Post
    R4 has an extra yellow mark, I think that gives it a high temperature rating. It measures 76K though it is coded 150K.
    The extra yellow band is a military reliability code, yellow = 100,000 hours (or .001%).
    This fifth band was commonly found on high-quality carbon composition resistors, particularly those from Allen-Bradley.

    The erroneous measurement is likely due to other current paths (resistance) shunting the 150K resistor.
    To make an accurate measurement you must unsolder one lead of the resistor and disconnect it from the circuit.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  5. #105
    Bill Burk's Avatar
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    Quote Originally Posted by ic-racer View Post
    Bill, if I can paraphrase your earlier post for clarity, you feel 10-2 setting gives 178 mcs based on your film tests, while Steve's unit measured 765 mcs on that same setting, right? (Nominal for that setting is 800 mcs)

    And, you don't know if the other settings are low also, right?
    Correct.

    Steve said something about my calibration being 681 mcs

    I based my estimate on these factors:

    -2.70 log mcs where 0.10 above B+F falls for 400 speed film (by definition)
    3.11 density estimated at the x-axis where this happens (3.11 of attenuation).
    1.84 density ND filter in the well (additional deliberate attenuation).

    This leads me to calculate 178 mcs effective light output at the test plane.

    Now I have some news. I just found a stop. The test plane is a little hazy. I was ignoring it. I was afraid to clean it because I didn't want to damage the test strip. But it's grungy. I took out the SEI and measured it against two different light sources. Several measurements are between 2.5 to 3 divisions. That means 0.25 to 0.3 density. Subtracting the calibrated 0.05 step (the supposedly clear step) leaves 0.20 to 0.25 unintentional attenuation.

    There is another acetate in the base which measures 0.03 on the densitometer. I believe a clean acrylic would have been included in the calibration.

    New calculated estimated light intensity:

    -2.70 log mcs where 0.10 above B+F falls for 400 speed film (by definition)
    +3.11 density estimated at the x-axis where this happens (3.11 of attenuation).
    +1.84 density ND filter in the well (additional deliberate attenuation).
    +0.25 (unintentional attenuation).
    =====
    2.50 log mcs, take antilog = 316 mcs

    681 mcs calibrated = 2.83 log mcs

    2.83 log mcs calibrated
    -2.50 log mcs estimated
    ====
    0.33 remaining discrepancy between estimate and calibration.

    A little over one stop lost light output. This is not looking so bad.

  6. #106

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    Wow you guys really nerded my thread up good.

  7. #107

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    How about going into town and renting a flashmeter and making some direct measurements, instead of all this guessing around based off of calculations from film densities?? I mean that's fine when you're sitting around at dinner working out the preliminary design of something on a napkin, but there's more direct ways to solve this issue.

    One pop of the unit and you will have your answer.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  8. #108
    ic-racer's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    How about going into town and renting a flashmeter and making some direct measurements, instead of all this guessing around based off of calculations from film densities?? I mean that's fine when you're sitting around at dinner working out the preliminary design of something on a napkin, but there's more direct ways to solve this issue.

    One pop of the unit and you will have your answer.
    Personally I think testing with film (as Bill did ) might be better (in a pragmatic sense; ease of use, easily available to anyone, etc.) than going off the results of a flashmeter. But that is certainly a point open for discussion with numerous advantages and disadvantages to each method.
    Last edited by ic-racer; 07-17-2012 at 10:15 AM. Click to view previous post history.

  9. #109
    ic-racer's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    The two I still have are 979 and 1290.

    PE
    Looks like mine is the oldest of the group. Again for the record, the only two service items I can tell in all the years of service are 1) Lamp replacement and 2) One failed carbon resistor.

  10. #110

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    Quote Originally Posted by ic-racer View Post
    Personally I think testing with film (as Bill did ) might be better (in a pragmatic sense; ease of use, easily available to anyone, etc.) than going off the results of a flashmeter. But that is certainly a point open for discussion with numerous advantages and disadvantages to each method.
    Well, sometimes certain tools are not available and work-arounds are what you have to do. But something that can read directly in Lux is much more direct.

    And what is easier to use - flashmeter vs. exposing film, developing film, calibrating densitometer, and then measuring film with densitometer. I think one of those routes probably has more opportunity for error as well.

    But as I have two flashmeters (a Minolta Flashmeter IV and a FlashMeter VI), I would not hesitate to test a sensitometer with it. And then, I would be worring about which of the two meters gave the most correct answer! (Although I think I would go with the FM VI since it is the newest of the two...)

    I'd also grab my color temp meter and check it for that as well, just for the fun of it.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!



 

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