Hi Joe,


This email is in response to your message to me concerning my ebay bid on a GAP/R K2-P. I looked at your PhilbrickArchive site - very nice. I am not a collector, however, when I saw the K2 for sale I thought that I might buy it as a conversation piece. Seems like the world has gone to digital processing today, even down to A/D conversion at the sensor location. Probably most electronics students today have never heard of George Philbrick or Loebe Julie. For such a simple basic circuit, the operational amplifier sure enabled a lot of advancements in technology.


I worked doing maintenance and modification to large analog and hybrid computers at a flight simulation lab at NASA Houston from 1965 to 1972. We had several Electronic Associates, Inc. (EAI) 231-R's, Applied Dynamics, Inc. (ADI) AD-80,s / AD-256's, and Comcor 5000's (Astrodata) analog computers interfaced to medium size mainframe computers and mini-computers. We also had three Packard Bell TRICE Digital Differential Analyzers. The TRICE was like an integrated parallel processor digital computer in a patchable analog computer form.


The operational amplifiers in the analog computers used very high precision wire-wound resistors made by JRL (Julie Research Labs) - Loebe Julie's company. My first boss started working for EAI in the late 1940's/early 1950's and I believe he said that he had met George Philbrick and Loebe Julie. A later boss had worked at the University of Illinois in development of the IILIAC series computers that used arrays of processors. Parallel digital processors were later used in real-time simulation. Another famous name in the field at that time is Granino Korn. Dr. Korn wrote several books on simulation with analog computers.


Due to the high cost of analog computers and the high cost of keeping them in spec., the simulation field evolved to putting more of the calculations on digital computers as they became faster and could handle the computing load. When I returned to Houston in 1977 and visited the flight simulation lab, they had added about thirty SEL-32 32-bit minicomputers that performed (in parallel processing arrays) the lion's share of the calculations and the analog computers were used only for interface to analog sensors and instruments. I have not been around real-time computer simulation since 1977. But considering the speed of computers today, I imagine that digital has replaced analog in even demanding applications, such as real-time flight simulation with a man-in-the-loop.


I hope your collecting and website goes well. The op amp/analog computing area is a very interesting part of electronics.


Tom Graves