Quoted from ebay auction #5745254649 by seller scinnimin:
"Up for auction, we have an George Philbrick Researches, Inc. operational amplifiers. One is a dual 9 pin to octal, in decent condition, except the keyway is broken a bit (still very useable), Gap/R model K2-W, serial#85555, and one 9pin and 7pin to, in good condition, Gap/R model K2-P, serial#73534 . The other 2 items in this lot are a DC to AC chopper that I took the guts out of for future octal plugin uses, and a solid state reference amplifier octal plugin that the guts have been taken out of. Both of these are in good condition, waiting for a new use. All of these were taken out of a Grass Instruments tube polygraph machine. "