[R-390] Collins Mechanical Filter History

[Kenneth]

This is the type of posting I would like to see more of. A historical
discussion on Collins mechanical filters is a good start.  In technological
history you do not concentrate on the technical aspects of such a device,
this is well known to all of us.  Getting inside the heads of the engineers
that designed it is what is important.  This type of discussion could be
expanded to such things as the Permeability Tuned Oscillator, which I
believe is what made a Collins designed receiver the great radios they are.
Such things as why a product detector was not installed in later models of
the R390A would be fascinating.  There are a couple of former Collins
employees who have been run off of this forum.  These engineers may be able
to shed some light on why this wasn't done. When you have a inside knowledge
of how a rig was designed when ever you work on any part of it not only are
you thinking about the repair but in the back of your mind is the knowledge
of who designed this section and why.  Which again goes back to what I have
said else where radios like the R390 series are like a book written by
engineers and understanding what is written there is what makes the care and
feeding of these fine old radios so interesting.

                       Ken de W7ITC