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  1. #21
    Steve Smith's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    They are voltage controlled attenuators - so if the lightbulb goes to the output of an oscillator and the CdS cell changes the amplifier volume - presto: tremelo...
    Perhaps on some lesser amplifiers! The good ones use modulated grid bias to create the tremolo.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  2. #22

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    Quote Originally Posted by Nicholas Lindan View Post
    You don't need a variac - just put a rectifier in series with the lamp as 1/2 wave rectified 120 VRMS is 83 VRMS. Beseler does just this when they put 83V lamps in an unregulated head.
    it should be less then that I believe. 120v peak to peak voltage would have an RMS value of .6xx (been far too long to remember). in a half wave recifier you would have about half of that value not counting any losses or inefficiency in the rectifier itself. also being half wave rectified ripple I would assume could be a problem.

    but as I've said been away from electronics quite some time so I've forgotten many things and I was never huge into it to begin with. just enough to get myself some analoge amplifiers and distortion pedals setup.

  3. #23
    Andrew Moxom's Avatar
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    Does this apply to the Beseler 45 Universal heads? This is the head with 3 82volt bulbs in it. One for each color!! I have a used one of these that has been fine for 18 months. My older 45 computer dichroic head with a single bulb used to have issues with voltage regulators, but nothing like a delay. I cannibalized other used heads to get it working again.
    Please check out my website www.amoxomphotography.com and APUG Portfolio .....

  4. #24
    Nicholas Lindan's Avatar
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    Another common issue with these heads, or any head that uses halogen lamps, is the lamp holder. They get corroded and munged up with age and need to be replaced. They are often the cause of random problems. Lamp holders are standard parts.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  5. #25

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    It Works!

    It appears to work just great! No delay, of course. The only question I have is my wiring. But, I was careful in tracing the wires and using the proper gauge. I bought a 6A8 rectifier just to make sure. I was able to use the original cord that powers the lamp, and thereby was able to wire my circuitry through the safety switch. So, nothing works if the lid is up.

    Must remember to turn on the fan, though. After rewiring, it's possible to turn on the lamp without the fan.

    My thanks to Nicholas and all for their contributions to this thread. The neat thing about this slick solution is that, I can still use the Beseler recommended light bulbs. Will order some extra.


    Quote Originally Posted by Nicholas Lindan View Post
    I should update this -- do NOT put a filter capacitor across the lightbulb: it will convert the 1/2 cycle AC at 83 VRMS to DC at ~160 volts (which is 160V RMS, as for DC the peak, average and RMS voltages are all the same). 160V RMS will make for a very short lamp life.

    The rectifier used should be rated at better than 600 volts and 5 amps. A rectifier diode similar to the 6A6, 6A8 or 6A10 would be appropriate:
    http://www.diodes.com/datasheets/ds28009.pdf
    There are many styles of rectifiers available that would work, one is certainly not limited to the above device.

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