HP 7970E - interest to split?

Chuck Guzis cclist at sydex.com
Sat Sep 30 12:47:31 CDT 2017

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.


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