Like "tunneldiode", most of my gear is from the '70s. I happen to think that the 1970s was a golden age of analogue design; it was before ICs were in widespread use, and those that you tended to see where fairly standard and easily obtainable or substitutable today. Designers then had to know how to use transistors, and the subtlety of some of the designs is amazing. So I guess that I'm not much help here.
Anyone know when the Telequipment Serviscope Minor dates from? I think that's the oldest I have, and it gets used now and then - never gone wrong in the 20 years I've had it. My son took it to pre-school when "O" was the letter of the day - I had to supply a note explaining what it was. (When it was "R", he took a Red Roberts Rambler Radio