What I found a little surprising is that on a 7970 head assembly, the DC resistance of the 9 track coils is about 76 ohms, but on the 7 track side, the resistance measures out to about 27 ohms.
Yet, both feed into the same read amplifiers. On the standard 7970 dual-mode drives, the switching between 7 and 9 track, is performed with a JFET on the input. I use small-signal DIP relays. I would have expected a big difference in the signal levels between the two. --Chuck
