The first tep was to
gut the monster and
wire in an AADE
digital frequency
display. I note with
glee that dreaded
dial cord and orange
indicator lying limp
on my work bench.
These radios are
notoriously badly out
of calibration when
purchased. I aligned
mine when I first got
it, and will post the
procedure later in
this project - for
those who are
happy with their
SR-III as purchased,
but want to "fix" the
frequency alignment.
Here is the DFD
tacked into the
circuit with the signal
coming from the
center pin of Q15
wired across the
varactor tuning
diode. it is buffered
with a 7 to 12pF
ceramic cap to
reduce loading the
tuning oscillator.
Not visible here is a
2 watt rheostat that
controls the
display's back-lit
LEDs from zero to
150mA. Notice that
having PC board
vices are almost
mandatory if you are
going to work on this
Ahhh, there's
another photo of
that rediculous, evil
orange indicator.
With all due respect,
I'll give it a proper
Actually, I'm really
not that sinister -  
have another SR-III
at the office that I'll
leave stock/standard
- out of respect..
Here are the
connection points.
Disregard the green
clip lead which is
being used to
monitor voltage
levels. The actual
oscillator signal
comes from the
RG-174 coax which
is tacked to the
capacitor feeding
the collector of Q15.
Ground is borrowed
from the top of the
IF can. If you look
very closely, you
can make out the
7pF coupling cap.
On the lower right of
the photo is the
tuning pot. Note that
I marked the legs "H"
and "L" to indicate
the up and down
frequency directions
of the pot's wiper for
future convenience.
The pot rotates
through 312
degrees. that is
much too fast for
tuning the full band.
The original dial
string and pulley
provided a ratio
reduction of about
8:1. I am going to
use a coarse and,
and a "fine tune"
(delta tune) pot
which will allow the
actual tuning to  
within approx. 10 Hz.
Adding a Frequency Counter to the SR-III
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