Well, after some further research, I managed to find the answer...
From Talkbass:
AMP (Amplified Music Products) was started in 1982 by two ex-Acoustic employees, Russ Allee (who designed the legendary Acoustic 360 amp) and Roger Smith. In '83, they hired Acoustic engineer Steve Rabe, who designed the SL-1 bass preamp to accompany the power amp.
Rabe left AMP in early '84 to start his own company, SWR Engineering.
From GK's website: ([Invalid or Expired Link Removed])
GK800RB was introduced in 1982.
Cheers,
Duff2