I have been given some bare PCB's to a dual-mono amplifier. I'm currently sourcing parts for it and seem to be struggling with the k1529/j200 MOSFETS indicated on the schematic, 16 total. They are not the easiest things to find and when I do find them, people are selling them for $20/pr. Can anyone make any recommendations for alternatives? The friend that gave me the boards told me that Motorola MJL21193/21194 were offered as an "upgrade." These I can find and source for about $40 total. Is this an upgrade? Will they work? Do I need to make any additional changes? Up until this point, I've only built and designed gain-clone style amplifiers. This is my first foray into analog devices.