George and DW
Definitely a 170uF Cap. I would check the ESR on that old cap very carefully, if it checks "good" for capacity, ESR and ripple, leave it alone. I just finished with a 577 and the filter caps all checked good for ESR and Ripple current. In my experience, the 577 was much more plagued with bad tantalum caps. I found 7 bad ones on mine, which completely disabled the thing. Just my opinion and experience, of course. Best of luck in your project.