That's a bit puzzling.
I was always intrigued as to how the hydro - throttle combination worked on our 1736 tractors.
On our 1736 you can set the throttle to a constant engine speed say 1,500 rpm and if you briefly push harder on the hydro peddle the engine will automatically rev up to the required rpms if it needs to, once you ease off on the peddle the engine speed will reduce back to your throttle setting of 1,500 rpms.
On tractors without this feature there would just be a direct mechanical linkage (cable) to the throttle lever. I'm only guessing for our 1736 there still is, then electronically there must be a controller interfacing with the hydro peddle to increase the engine rpms as required????