Rebuilding my old analog console

[Kevint]

Laserist - let me think about what you posted. But the scan amp I posted is what I am currently using to drive my g100/120's, and for now I just put a joystick as shown to move the images around on the wall.

Mixedgas - that looks like a good improvement over my current scan amp which does no have any adjustments to improve the image quality. I would like to prototype it but could use your help with some of the lettering and how to configure them.

A = +15V
L = -15V
B = OUTPUT FROM MY SCAN AMP
E/F = ROUTE TO GROUND
C/J/D = NOT SURE HOW TO CONFIGURE THE INPUT.

THANK YOU BOTH

[lasermaster1977]

I started out with G-115 open-loop galvos, eight of them, 4 XY pairs, to start out with for Red, Yellow, Green. Blue beams. It was a big investment for me at the time and I couldn't afford to accidently destroy even one of them. So I took a very conservative approach to protect my investment and used the Fairchild uA791 power op amp DIP ICs for each galvo. The 791 could drive up to 1 amp of current into a low impedance load and was current limited to 1 amp on either polarity. Attached is the simple, inverting op amp schematic I used and the 791 datasheet. I still have these original ICs and spares and never experienced an IC failure after years of operation. It is a shame they are not longer available as I also used the same drive amp schematic to drive my two DC chopper motors referenced in the "Back then...this is what we did" thread, on page 9.



ua791.pdf

A variation to the GS A-102 Driver that mixedgas provided is one I used here:


They work quite well at modestly extending the frequency response and step response of the G100-120 open-loop galvos. But the trade-off for this back EMF feedback is about a 50% reduction in the maximum scan angle.

On an artistic note, I rather liked the visual looping scan effects one got on "corners" from driving open-loop galvos near there resonant frequencies with square waveforms.

[mixedgas]

C,D,J are a 10K potentiometer for offset.. If you leave J floating the amplifier will zero to ground. J would be the wiper for the offset potentiometer or gasp! Joystick...



Steve

[Kevint]

Mixedgas: CJD input - got it. Thank you very much.

Lasermaster1977: thank you for the designs and image photos. I did acquire some g100's from Gary on this forum. That plus what I had, I am able to get 4 XY scan sets and have a couple of galvos available for chopping and other effects. Still debating whether I do a 2 or 4 scanner system.

Decisions, decisions, decisions. I will have to order some transistors to be able to test both designs. I totally miss the days of having the dale electronics, radio shack or fry's to pick this stuff up at. I will need to order: 2N4922/19, 2N6121/24, RC4136N and LM301A. The only power transistors I have are TIP41/42. Very curious to see the performance difference compared to my current scan amp. My current amp isn't all that great.

[lasermaster1977]

Mixedgas: CJD input - got it. Thank you very much.

Lasermaster1977: thank you for the designs and image photos. I did acquire some g100's from Gary on this forum. That plus what I had, I am able to get 4 XY scan sets and have a couple of galvos available for chopping and other effects. Still debating whether I do a 2 or 4 scanner system.

Decisions, decisions, decisions. I will have to order some transistors to be able to test both designs. I totally miss the days of having the dale electronics, radio shack or fry's to pick this stuff up at. I will need to order: 2N4922/19, 2N6121/24, RC4136N and LM301A. The only power transistors I have are TIP41/42. Very curious to see the performance difference compared to my current scan amp. My current amp isn't all that great.

The output transistors are not that critical. You can use your TIP41/42 instead of the 2N6121/6124.

Here are photos of the A-102 circuit board schematic and my schematic.

A-102



My schematic similar to mixedgas' (in this version I used 7815 and 7915 voltage regulators)

[Kevint]

Thank you Lasermaster1977

I having an issue with image proportions. Please see attached photo. I get a nice round circle with one scan set, but the other scan set produces a tilted oval. I measured the voltages out of each scan amp and they are equal. I switched the scanner sets outputs from the scan amps and the oval shape did not move to the other scanner set, so I think it is a scanner issue. If so, is there any way to correct it?

[Kevint]

Here the 2 scan pairs with a simple image running

[mixedgas]

You can replace the opamps with Tl081, Tl082, or Tl084

singles, duals, quads respectively.

Tl07x would work as well.

if you have unused opamps in a pair or quad pull both inputs to ground with 10k resistors.

the more modern TIP transistors are just fine. In which case you can dispose of the little "base boost" transistors and just use the TIPs.

You might want to look at "Amplified Parts Inc." in Phoenix AZ for old school parts and beautiful colored knobs.


Steve

[Kevint]

Mixedgas: Wow! Your are not kidding, KNOBS of plenty.

Thanks for alternate part ideas. I'm hoping that with an improved scan amp it might help alleviate the above mentioned oval image issue. issue.

[mixedgas]

That's a source balance issue in your image. So you may have to put a potentiometer on one output phase of that oscillator chip. Phase looks a little tilted, take a look at how well the oscillator capacitors match in value, too.
4423 are wonderful, but can be a bit funky if unbalanced or the capacitors do not have low Effective Series Resistance or Matching ESR. There is a priority list in the 4423 data sheet on what caps have low ESR in order of technology.
For the cost of an ESR meter you can order a couple of dozen caps, so... However some of the cheap capacitance meters on Ebay/Amazon can be remarkably accurate if all you care about is a relative measurement, and in this case, matching is what's relevant. 4423 is basically a Navy part for various uses in servos, synchros, sonar, analog computing , etc.. So a bit of tuning in the final app was OK.


Here is the relevant page of EE Gobblydgook. I actually prefer teflon, polycarbonate, or polystyrene due to easy matching, They are wound, not cast. Some ceramics unless you order 1% grade NPO are all over the place, and voltage sensitive. Orange Drops are pretty ideal as wound tape based. NPO is a different grade of ceramic designed for temperature low drift and low dissipation / lower ESR




Steve