The Story Of The Ampex 602 Tape Recorder. (USA)
The 600, 612 and 601 used a 6F5 input tube for repro[duction]. The 6F5 is an old metal tube with a grid cap. As time went on, fewer and fewer tube manufacturers made it. Finally, we were down to one: RCA.
All of a sudden one day the 601s on the assembly line had awful hum. We discovered that RCA had changed the filament design from a coiled (self-shielding) one to a W-design like you see in a light bulb. Hum-osis!
Frantic call to RCA. They said, that we were practically their only remaining customer for these and they would not change back to the old design.
Panicsville at Ampex! We needed a new design--fast! Bob looked at what we had and decided that we could cram the PR-10-1 circuits into the 600/601-sized chassis. So that was done, and the entire project took only about 6 weeks from start to production. Much cussing to get stuff in there...
The 602 was given a new paint job (chocolate) and for the first time 602-2 owners could independently record both channels and use the "back" side of a tape; the 601-2 used a full-track erase head.