Ye Ol' G115 and G120PD Scanners

[Draco]

I am some what embarrassed by this question as i found when i needed to repair my projector and found i forgot to mark what should be the positive connection, is the red and green the positive when in parallel ? or does it even matter as long as they are phased correctly?

[lasermaster1977]

I am some what embarrassed by this question as i found when i needed to repair my projector and found i forgot to mark what should be the positive connection, is the red and green the positive when in parallel ? or does it even matter as long as they are phased correctly?

No worries. Connecting Red/Green and Yellow/Black would yield a parallel connection. Drive inputs to these two pairs and results in a 4ohm impedance. Connecting Black and Green would yield a series connection with the Red and Yellow leads as the drive inputs and results in an 8ohm impedance.

Whether the resulting two leads are connected to the drive terminals one way or the other doesn't matter as they can be switched to change directional polarity.

[cmarkus]

Hello everyone, I just purchased for my research group a G300PD for a simple application but I haven't been able to find any drivers for it on the usual surplus distributors. I was hoping to have something set up before it arrived. All I am looking to do is drive it with a triangle wave ~1 degree at 50 Hz using a spare function generator. Any advice would be much appreciated!

[lasermaster1977]

Hello everyone, I just purchased for my research group a G300PD for a simple application but I haven't been able to find any drivers for it on the usual surplus distributors. I was hoping to have something set up before it arrived. All I am looking to do is drive it with a triangle wave ~1 degree at 50 Hz using a spare function generator. Any advice would be much appreciated!

Here is a schematic of the General Scanner A601 drive amp used for the 100PD & 300PD scanners. Sorry that it is in two pages but I can't scan large sheets. The two pages should just piece together just fine.

Note in the lower right of the right-half page the block denoting values of resistors and capacitors for the 100 vs the 300 scanner. Plus and minus 15 volt regulated supplies at about 1-2 amps for each polarity where normally used.



It's not much to offer, but I hope this helps, as there are better designs. You could change out the darlington current drivers to something more beefy and increase the power to the darlington drivers to 24-35 volts while leaving the op-amp circuitry at +- 15v regulated.

[cmarkus]

Thanks! General Scanning wasn't able to pull up any of the old documentation so this is very helpful. I doubt I'll be needing much more power, but I'll think about modification if I need to beef it up a bit.

[LaserCo]

thanks for all the circuits and info lasermaster1977.
I have stuck both pages back together with some amazing glue

A601 Driver for G100PD and G300PD Galvos

[lasermaster1977]

thanks for all the circuits and info lasermaster1977.
I have stuck both pages back together with some amazing glue

A601 Driver for G100PD and G300PD Galvos

Awesome. Poly-molecular bonding no doubt....

[Draco]

this might have come a little to late to the other poster but if all you need is an open loop amp with a differential output i find that a low to mid power car audio amp works, most have an internal supply that generates the positive and negative rails at the current needed for the deflection of a few degrees. Building the original driver on the other hand would be more entertaining, and when these car amps fail they can some times output DC, most have fusible parts and a DC detection though

I have seen the A601 on Fleabay but almost always untested and over priced

[lasermaster1977]

this might have come a little to late to the other poster but if all you need is an open loop amp with a differential output i find that a low to mid power car audio amp works, most have an internal supply that generates the positive and negative rails at the current needed for the deflection of a few degrees. Building the original driver on the other hand would be more entertaining, and when these car amps fail they can some times output DC, most have fusible parts and a DC detection though

I have seen the A601 on Fleabay but almost always untested and over priced

Draco, that's an interesting idea for using car audio amps. Are they DC coupled? A601 amps are over-kill for driving GS100/300 series open loop galvos.

I don't know if these op-amps are still available today or if there are better equivalents that have as low a parts count when used in a circuit, but for my first open loop galvo amps I used a Fairchild uA791P power op-amp for each axis. I liked these for this task because they were inexpensive, required a small parts count of resistors and capacitors, had built-in current limiting to 1 amp, short circuit and thermal protection. They also protected my G115's from being over driven for which there were RYGB XY pairs. Back then they were the 2nd biggest big ticket item next to the ion gas lasers.



As you can see from my schematic, the only moving parts are two thumbwheel type trip pots, one for gain balance and one for DC offset zero-trim.

Here's the datasheet for the 791.
http://radio-hobby.org/uploads/datasheets/ua/ua791.pdf

I still have quite a few of these. The 791 DIP package had better heat sink tabs so I only used these. For heatsinks I used some 3/16" aluminum panel stock for 1" x 2" sinks, one for each IC heatsink tab folded vertically, secured with a 4-40 nut and bolt (shown in photo). Each 791 had it's own dedicated 7812 & 7912 regulated power supply IC, that were both mounted on a 3/16" x 1" x 5" heatsink. I had the 791 set for a gain of 10 for use with a 1-2v peak-to-peak input, with DC offset trim pot and gain trim pot for XY size balance.

I used the Augat rivet socket style IC socket (shown above for these guys since they were so heavy duty) and for there current carrying capability.

I never had one of these IC amps fail and they were in constant service for over 5 years, doing an average of 12 1-hour planetarium laser shows per week including countless outside gigs and special shows. I still have everyone I ever used or purchased (the chips and sockets were salvaged so their prototype edge connector boards could be re-purposed. I am planning to recreate some open-loop op amps with them again just for fun because they were such a great 1-amp driver.

[mixedgas]

Why not just build an A102 Back-EMF and try that. Adds damping so you can follow square waves.

Steve

See attached.