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Thread: Ye Ol' G115 and G120PD Scanners

  1. #1
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    Default Ye Ol' G115 and G120PD Scanners

    After years, na decades, of dormancy I'm almost ready to fire these puppies up. It should be interesting. And yes, those are original General Scanning mirrors and mirror mounts.

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  2. #2
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    Have you put different connectors on the end of the G120PD's?
    My understanding is that the "D" part of the model name indicates that it has a "DB" connector on its end.

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    Quote Originally Posted by LaserCo View Post
    Have you put different connectors on the end of the G120PD's?
    My understanding is that the "D" part of the model name indicates that it has a "DB" connector on its end.
    Actually, in the olden days of General Scanning, PD stood for Position Detection or Positioning Device. All PD's back then came with Amphenol connectors. It was later when they abbreviated it to "P" so that "PD" could indicate a DB style connector. I don't have the time right now, but I will scan and upload the original GS materials that show this, later tonight.
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    just out of curiosity would you have into on there P310? i have pins outs but that was all, was just wondering what current they can tolerate, when they where made, just technical gooey stuff lol
    I am actively using a set in a projection system i use with music
    Last edited by Draco; 01-30-2015 at 17:55.
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  5. #5
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    Quote Originally Posted by Draco View Post
    just out of curiosity would you have into on there P310? i have pins outs but that was all, was just wondering what current they can tolerate, when they where made, just technical gooey stuff lol I am actively using a set in a projection system i use with music
    Draco, I just happen to have the G-300PD product line sheet from April 1978 with the tech specs. The G310 was the 10 degree mechanical/ 20 degree optical scan angle version. WARNING:It's pretty gooey. The G-100PD and 300PD used the same Amphenol 127-216 5-pin connector with the same pin-outs. The PDT versions used the 7-pin version to accommodate the heater blanket. (At least that's my best recollection. )

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    And here is the GS Optical Products Price List sheet from 1978 with my notes on some item pricing in 1982 and 83.
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    Here is the GS Unpacking Instructions
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    Here is the G100-G300 Operating Instructions
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    Here are the G100PD-G300PD and PDT Interconnection Diagram
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    One 1983 color product brochure I have from GS does show the DB-9 connector in use on their product line so I'm pretty sure the change from Amphenol to DB-9 occurred sometime prior to '83 but not too much before then.
    Last edited by lasermaster1977; 01-30-2015 at 20:35.
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    Thank you for the info!
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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    I have a question? I noticed the G300 are connected in series per the instructions, the G310 that i have are in parallel, i had wired them from some crappy picture i found on goggle and months back, they give me a dc resistance of about 7 ohms, i have conflicting info now and was wondering witch configuration is correct or safe to operate at?
    The deflection I am driving them at is less then 10 degrees from center worse case, 5 degrees from center is more typical but i don't have an accurate way to measure that
    Last edited by Draco; 02-03-2015 at 12:06.
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  8. #8
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    Quote Originally Posted by Draco View Post
    I have a question? I noticed the G300 are connected in series per the instructions, the G310 that i have are in parallel, i had wired them from some crappy picture i found on goggle and months back, they give me a dc resistance of about 7 ohms, i have conflicting info now and was wondering witch configuration is correct or safe to operate at?
    The deflection I am driving them at is less then 10 degrees from center worse case, 5 degrees from center is more typical but i don't have an accurate way to measure that
    These GS open-loop scanners could be wired in series or parallel. The 100, 300 series came with all 4 coil leads open. The user could decide whether to run the 100's in series (8 ohm) or parallel (4 ohm) and the 300's in series (16 ohm) or parallel (8 ohms). The 300's coil impedance in parallel was 8 plus or minus 1 ohm. So 7 ohms is within specs. The user's application usually dictated how they intended to drive them (lower power/higher impedance or higher power/lower impedance) and what level of performance they desired from the scanner.

    I always ran my GS100's in series so they represented an 8 ohm load to my driver. Initially I used a Fairchild 791 power op-amp as an open loop driver for each axis. I had four XY pairs (RYGB). The 791 was capable of driving an 8-ohm load to 1amp with plus and minus 12 volt supplies. I had a one amp fuse in series with each scanner and never blew a fuse, and could drive the scanners to their limits. The 791 also had a nice feature of built-in current fold-over, current limiting above 1 amp. Now this little power op-amp that could served me well for over four years in this application. I also used them as drivers for motors and solenoids.

    Eventually I went to a closed-loop driver using a back EMF feedback type of driver that used balanced Darlington power drivers, a 1 ohm current sensing resistor in series with the scanner coil and 4136 op-amps on the front-end and back EMF feedback loops. This driver used LM7815/7915 voltage regulators on the op-amps and plus/minus 24 volts unregulated on the Darlington drivers. The Darlington pair was a 2N2222 and 2N6121 on the positive drive rail and a 2N2907 with a 2N6124 on the negative drive rail.

    Where open-loop the GS115's would provide a 30deg. optical scan angle easily, when run in back EMF closed-loop you could only expect a 15deg. optical scan angle but you got much better linearity over the first half of the open-loop bandwidth. If I remember right, open-loop 3db roll-off point was around 300-400 Hz, somewhere in there. Closed-loop it was around 150-200 Hz but far, far better step-response with no to very little over-shoot.

    Bear in mind that I mainly used the G120PDs for main-line customer graphics and scanner effects, and only used the G115's with the quasi-back EMF, closed-loop driver for disco-type rental installations that didn't need huge angle of scans and modest Lissajous/graphic image scan effects.

    Sorry if I digressed.
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  9. #9
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    I heard you can measure the back EMF to get more precision with those open loop galvos .
    Wonder how that worked out back then.

  10. #10
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    Quote Originally Posted by masterpj View Post
    I heard you can measure the back EMF to get more precision with those open loop galvos .
    Wonder how that worked out back then.
    Who in hell would want to do that?
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