Beseler Resistrol

Discussion in 'Darkroom Equipment' started by ignacj, Mar 19, 2010.

  1. ignacj

    ignacj Member

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    Does anyone have and use Beseler Resistrol? If so, what voltage range do you get with it?
    Mine came brand old/new from *bay. the unit seems to be brand new, but the lowest I can get voltage is 90V (from 110V). Is this normal or do I have faulty unit?

    Also, any issues when printing with VC paper?

    Thank you
    ig
     
  2. Chan Tran

    Chan Tran Member

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    I used the resistrol a long time ago. The voltage that you get depending on the wattage of your bulb but if I remember correctly it's about from 80V to supply voltage with a 70W bulb. If you always set the resitrol to get the same voltage all the time then there is no problem. If you varying the voltage to get the lamp dimmer or brighter then the color of the light also changes and could cause problem with VC printing.
     
  3. ignacj

    ignacj Member

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    Chan,

    My understanding is that with household AC source, voltage is constant and amperage varies depending on lamp or appliance being powered. That why we have current limiting fuses. Resistrol should be changing voltage by providing variable resistance in series with a lamp. My question is how wide is that variation with Beseler Resistrol on min and max. I was expecting wider spread then 20 volts. Then in other hand, Resistrol is simple wire coil, so I would imagine it can only go so much before it would overheat. Perhaps 20V spread is to be expected?
     
  4. GaryFlorida

    GaryFlorida Member

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    what is the purpose of the resistrol? If it is just to control the brightness of the enlarger bulb wouldnt a dimmer switch work just as well?
     
  5. fotch

    fotch Member

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    Not true. I will adjust incoming voltage (USA probably somewhere between 110v to 120v) and lower the voltage, thereby dimming to light, of any bulb. Kind of obsolete system now.
     
  6. rjmeyer314

    rjmeyer314 Member

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    I had the same problem with my resistrol, not enough range when I was controlling the brightness of my point source head. (You don't use the diaphragm when using the point source head, you want the lens wide open.) I gave upon it and switched to a variac unit made by the Time-o-lite people. That solved the problem.
     
  7. 480sparky

    480sparky Member

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    Dimmer do not work by 'reducing' voltage. They work by clipping the AC sine wave.

    Normal sine wave:

    [​IMG]


    Clipped sine wave:

    [​IMG]

    Basically, the circuit is turned off (0 volts) for a portion of the 1/120th sec of the sine wave, then turned back on. This clipping causes the RMS (root-mean-square) voltage of circuit to be lower. Peak voltage (in 120v systems, it's 169.71 volts) remains the same.

    This is also why some dimmers cause incandescent lamps to 'hum'... they're being turned off and on very quickly causing the filaments to vibrate, which we hear as 'hum'.


    That said, my 150 lamp will run from 68-112 volts.
     
    Last edited by a moderator: Mar 19, 2015