[R-390] Tuning linearity

[Tisha Hayes]

The deal with the HP-606A sounded like an interesting challenge. I think
your solution would be very applicable in many radios other than in a
permeability tuned radio such as the R-390A and most vintage car radios. As
most know we can adjust the linearity of an R-390A tuning through the
compensator disc and it's million tiny screws on the PTO.

If you have ever chased the tuning on a radio that was wildly out of
alignment you know that you can get what appears to be "decent" spots. As a
youngster I had a Soundesign clock radio that could barely pick up WLS
Chicago at night. I decided to "tune it up" and as a bit of a neatness freak
throught that those little yellow, red and green screws on the metallic
tuning cans should really all be tightened down snug. Then I tried to tune
the radio with the two or three tiny little capacitors on the back of the
main tuning cap.

After a bunch of misguided tweaking and pure luck I ended up getting WLS at
890 KHz but it was way down at the 540 KHz side of the tuning dial. Sweeping
the tuning dial up on the radio I found that it was filled with Morse code,
some AM voice, SSB in the 160 meter band and a few international shortwave
broadcasters. I borrowed a few of my dad's alligator clips and attached the
rather wimpy line cord wrapped FM antenna lead to my bedsprings.  I left
that radio in that state of mis-tuning until I was out of high school and on
my way to college.



-- 
Ms. Tisha Hayes