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Acocte practice oscillator is practically
always a simple affair. But wit h a
good fC , suc h as Motorola's HEP 570 , the
project can be ma de even simpler while the
circ uitry it self - wit hin the in teg rated
circuit - sta ys complex en ough to assure
plenty o f au di o gain, good stability, and
excellent qu ality of ton e.
The oscillator described her e was
designed by experts at Motorola, who
allowed for f'our "discrete" st ages, each
with a t wo-transistor capability , within the
framew ork of the lone fla tpack l C package .
One o f t he nicest features of the HEP 570
as th e osc illat or eleme n t is its economy o f
ext ernal parts. Apart from the pow er
swi tch , the telegraph key, the speaker, and
th e battery, the only additional
comp o ne nts required ar e two resistors, a
pot, an d three ca paci t ors. What co uld be
simp ler?
Con structi on is as sim ple as the
schematic (Fig. 1) makes it seem. One ite m
no t shown on the schematic, however,
could make the job easier and save the
insec ur e builder a great deal of grief: a
FEBRUARY 1971
suitable soc ke t for th e IC. An advantage o f
usin g IC sockets is that if all do es not go
well right off, the IC remains isolat ed from
the res t of t he circuit while changes are
incorporated. Also , mo st hams use their
ICs again and agai n, for any numb er of
ap propriate pr ojects. Soldering of an l C
directly into a circuit will seriously cur tail
its u nive rsal utility. The packag e can't
stand too many sold er/unsolder op erations
be fore the leads give out. But with a
socket , th e IC stays like new and may be
used in as many projects as the builder ha s
sockets for. And changing th e IC fro m one
project t o another is no more difficult t ha n
ma king a tube change in an old-fashioned
rig.
Your ju nkbox will und oubt edly yield
t he resistors and capacitors necessary to
comp lete the oscillator project, but it is
unlikely that you'II find t he right speak er
kicking around the shack . Since the output
of the amp lifier/oscillator is in th e vicinity
of 50n, a sta nd ard " in tercom-type"
speaker is required . If the expense o f su ch
a speaker proves a bit much, there are
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