Replacement balance
Thanks for posting! Your channel balance appears to be an older, discontinued Crossbow balance. The good news is that we do have a replacement solution that will work for you.
To determine the correct replacement, I'll need to know the length of the balance, the width of the bottom shoe, and the exact weight of the sash. You'll also need to include a photo of how the balance attaches at the top of the window channel. Please also confirm the diameter of the spring; I believe it should be 1/2".
Take a look at the video tutorial below as a reference when gathering the requested information. We show how to obtain the length as well as how to remove and install the hardware.