It's LM108 and LM112 (internally compensated) and there is de facto no trick there. It's 1nA enter bias which is quite steady with temperature as in many bipolar opamps since β really increases with temperature. Later on iterations like LT1008/LT1012 or OP97 pushed it down to I have been working https://caidenhfaum.blog2news.com/34833884/5-tips-about-coaxial-switch-you-can-use-today