For those with an interest in the subject devices, another member, Orin, and I have developed a schematic and model of the Chopper Stabilized Amplifier (CSA) that seems to model the actual to a high degree of accuracy. I will post it up someplace if given a target location. My particular device is now waiting for the original NMOS4 FETs, MFE3002, that should be arriving shortly. The units seem to require some degree of matching but we aren’t sure at this point. Mine is running well with ECG220’s installed but I had to play around to find two that worked. This could have been due to dual device failure. Anyway, Orin jumped in and found an error in the chopper and then was bright enough to add the NMOS4 devices which fixed the model and off it runs. Having spent hours and hours on both the real and model, I must say that I woke up to Orin’s email and it made my day. Thanks to all that jumped in. Jerry