Some of the other analog companies that come to mind are Applied Dynamics, Comcor, Systron Donner, Computer Systems Inc. and a few others I can no longer remember. I also worked for Hybrid Systems in Houston, which made big analogs and hybrids for aerospace and petrochemical companies. The digital computer we used was the IBM 360/44 that was the "hot" engineering/scientific Fortran machine. I worked on one system that went to Bell Helicopter in Fort Worth where they simulated their helicopter designs. Think Huey.
Most of these analogs were of the iterative type where fast integrators were used and the problem was time scaled and solved repeatedly many times per second. This allowed you to display the graphical results on an oscilloscope. It allowed dynamic interaction with the solution that helped visualize the problems and optimize designs.
A few other companies used to make components for analog computers—many of which were constructed for general and special purpose applications. George A. Philbrick (GAP) was one of these. I first learned op amps using their K2W vacuum tube op amp module with two 12AX7 tubes. You may remember reading in Bob Pease's column about this device. Later GAP made solid state op amps, some of which Bob Pease designed. Burr Brown (now part of TI) was another early solid state op amp maker whose early products I sampled.
When I worked for Heathkit in the late 70' and 80's I saw some examples of their old kit analog computer that had been discontinued by the time I worked there. The EC-1 was a small (9 op amps) but useful educational computer. Their op amps were a single 6U8 dual triode-pentode with an open loop gain of only 1000, but it was enough to work moderately well. The main problem with all these early op amps was that you had to balance them to get the DC offset out for maximum precision. That was done manually with a pot and once all your amps were balanced, one or more would start drifting out of balance. You had to run your solution fast. Heathkit also had a large machine called the EC-400 which had 15 op amps if I remember correctly. Both worked good as long as the the DC drift was balanced out.
Solid state op amps soon became available, but few could operate over the ± 100 volt analog range used in most analogs. A few ± 10 volt machines were available, but most did not give the required precision or dynamic range. Making a wideband op amp with that ± 100 volt range back in the late 1960s and early 1970s was an amazing accomplishment. It still is today.
Today we have such good op amps, analog multipliers, and other superior analog computing components, I have sometimes wondered if we shouldn't bring back a modern version of an analog computer. Does that make sense? Maybe it could be a solution to some ugly calculus-intensive problem like in a research situation. A special analog computer could be built to simulate the equations quickly and with the ability to play around with the various variables and so on. It would certainly be smaller, cheaper and more precise than the monsters of yesteryear. Analog is still inherently faster than digital so maybe it could happen. Then again, maybe not.
Anyway, this is a lost technology. With digital computers faster than ever and now with DSP and super simulation and math software, who needs an analog computer? What a shame. But I guess we can say that about many other lost electronic technologies.