A process for producing ammonia make-up synthesis gas and a procedure for revamping a front-end of an ammonia plant for producing ammonia make-up synthesis gas are disclosed, wherein the make-up synthesis gas is produced by means of steam reforming of a hydrocarbon gaseous feedstock; said front-end includes a primary reformer, a secondary reformer, a shift conversion section, a CO2 removal section and optionally a methanation section; a shell-and-tube gas-heated reformer is installed after said secondary reformer, and a portion of the available feedstock is reformed in the tubes of said gas-heated reformer, and heat is provided to the shell side of said gas-heated reformer by at least a portion of product gas leaving the secondary reformer, possibly mixed with product gas leaving the tubes of said gas-heated reformer.