I wonder if every undergrad electronics course at the time had a “build a differential amp out of crappy JFETs” as an assigment!
AD does indeed still sell matched BJT pairs. http://www.analog.com/media/en/technical-documentation/data-sheets/SSM2212.pdf is typical.
Yeah, as I said, offset compensation was the real issue, because the varying beta was manageable. (Except for the fact that you kill the bandwidth, but for a mechanical plotter who cared?) I can just picture you running madly between the rooms trying to tame that setup! (And I can recall pushing the cases of a couple of 2N109’s together with grease in between, in hopes of having good enough thermal coupling to keep them matched for at least a few seconds. I think I was maybe eleven at the time.)
When it comes to electronics, we’re living in the good old days.
