Hi Robin! A few ideas ...
Our gym has add-on weights that look like black rubber bricks. They come in 5# and 7.5# and are made to fit on top of the weight stack. If your gym has something like that, you'd be able to do smaller jumps in weights. You're right, it would be very tough to jump ten pounds each set.
Or ... keep on using free weights.
Or ... if you want to use machines, switch to a more traditional rep scheme of say, three sets at X weight (something that's challenging at 10-12 reps).
Because all machines are different, it's hard to say what weight you should be lifting. I can give you an idea what I start a new gym member out at on LifeFitness machines, but wouldn't be surprised at all if you can lift 50% more since you're experienced
.
This is where I'd start a beginner on machines:
Chest press - 30#
Back row - 30#
Lat pulldowns - 30 or 45#
Pec flyes - 15 or 20# (ours goes in 15# increments so I'd add a 5# brick)
Incline press - 15 or 22.5#
Shoulder press - 20#
Lateral raises - 20#
Arm curl - 20 or 25#
Arm extension (triceps) - 20#
As you can see, I use the 5 and 7.5# weights a lot! Keep in mind that there's a lot of variability between different brands of machines and you may be able to do more or less on different machines.
Hope this helps a bit.