non Tilt window/balance.

Thanks for posting. I am confident we can help, but that stamp is not an identifier. It just tells us the strength of the balance. If you can remove the balance and send us photos of the nylon attachments at both ends, we should be able to narrow this down. 

Does the bottom nylon attachment have 'wings' or side tabs like the top attachment does? It's tough to tell from the angle of the photo. If both attachments have wings, I believe this is either an S380-19 or S385-19 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon attachment, or what is also called the shoe. See below. Measure your old balance's shoe depth to see what matches best. For a stamp option choose 1850.

Comparison of the S378, S380 and S385 balance shoes.