Is there a data sheet for the LL1518?

No, I am afraid we have no data sheet for the LL1518. The LL1518 is a (solid state) line output transformer, similar to the LL1517.

Usage:

Turns ratio 1:1    
In+		pin 1 (left bottom, if you read transformer label correctly)
In-		pin 5    
Out+		pin 7   
Out - 	pin 10 (right top)  
Connect	pin 6 + 9  
Ground 		pin 8    
Turns ratio 2:1    
In+		pin 1 (left bottom, if you read transformer label correctly)  
In-		pin 5    
Out+		pin 7 + pin 9  
Out - 		pin 10 + pin 6  
Ground		pin 8