You could always do barbell rows or one arm DB rows.
When my power rack arrived, I got rid of the machine I had, for lack of room. With it went my capability to do lat pulldowns.
I'm doing the program that alternates like so:
Workout A
Squat
Bench Press
Deadlift
Workout B
Squat
Press
Chinups or Lat Pulldowns
Al
Problem: not only can I not do lat pulldowns for lack of equipment, I am not strong enough to chin myself even once.
Should I just do deadlifts every workout, keep trying to chin myself in hopes of getting strong enough eventually to do so, or something else? I'm not going to join a gym just so I can do lat pulldowns once a week.... ;^) (Although I actually do like lat pulldowns).
Interesting discovery, btw: It's harder to lift the same amount of weight with free weights than with a machine. I've always heard that, but now I really believe it. Also, talk about shaking like a bowl full of jello when pressing a mere 75# (my work sets for today).
Also, man, I can really feel it when I'm not recovered. The first two days after the workout are hell. I don't want to do anything but sleep and eat. Luckily, I'm retired, so I can actually do that!
You could always do barbell rows or one arm DB rows.
Oldster (hope he's OK these days) always swore by T-bar rows. I usually managed to hurt my lower back with them.
So I've seen this several times--women doing a barbell strength training program have never tried doing a chin-up, and then they try one and get it after just benching and pressing. Apparently, the general strength you get in your upper body is sufficient to drive progress in chins even if you do not specifically train for them. You could try curls if you like, or get some elastic bands to train chin-ups with assistance. But they might just get easier as you get stronger overall.
I trained chin-ups by working with jumping chins and slow negatives--you jump up to the bar, then slowly come down, repeat. Lat pulldowns never did much for my ability to do a chin-up that I could tell.
If you're only pressing 75lbs then at this stage you might find Dan John's "bat wings" useful. Face-down on the bench, dumbbells/plates on either side, row the weights up - try to shove your thumbs into your armpits and shove your elbows back and together, pause at the top for a three-count. Do a few sets of 10 or so, the load's not super-important really, 20-30lbs is plenty. This is pretty useful for helping to learn to keep the upper back tight in SQ/BP/DL.
Once you're squatting and deadlifting 225lbs or so for work sets this won't be as relevant, and you'll possibly be able to do chinups anyway. Depends on your age and condition.
@Kyle - As to my age, I'll be 68 in two months. My condition is okay, but for two herniated spinal disks, which I am loathe to aggravate. I tend to stay away from things like rows because of that. I know Rip says you WILL get injured, but I'll do everything I can to avoid injury at my age.
@tobo - I like the idea of curls as a substitute, since I have a curl bar already.
As for my 75# press, it seems pathetic, but according to Kilgore's standards for my age group (over sixty, in my case, way over sixty) another 25# at 1RM will put me in the advanced category, so it's not as pathetic as it seems, I guess.
My personal goal at this point is to make "advanced" in those standards on all my exercises. I'm not far away on press and bench, but have a long way to go on squat and deadlift. Anyway, something for me to shoot for.
At 68 you're already ahead of the curve by doing any training at all.
I have had good results with women, fat young men and older people using assisted chins and pullups. I had good results earlier with machine-assisted chins, got my 44 year old sister up to 5x5 bodyweight chins in 3 months after starting with about 25 kilos of assistance.
Later I didn't have access to those machines so I tried the bands, the heavyish ones used a lot in powerlifting training. We have a set of 5 different thicknesses. I looped them over the chin bar, then had the trainee step in the loop. They work with 3 sets of 5-8 in a progressive manner similar to SS.
Here's a video https://www.youtube.com/watch?v=JFtE27GzTTk