MEET MR.
FET
(Continued
from page 53)
Fig. 12. This high-
frequency
crystal
-controlled os-
cillator employing a Siliconix
2N2608
p- channel
FET has a useful operating
range
of
1 megahertz.
tion
is
the
most popular, and
corresponds
to the common
-cathode tube circuit
ar-
rangement.
Typical
FET
circuits are
illustrated
in Figs. 11 through
14.
Figure 11 is
a
FET
voltmeter with a
matched
pair
of p- channel
FET's
(Q1
and Q2) used
in
a
differential
amplifier
arrangement.
In general,
FET voltme-
ters compare
favorably
with good
-qual-
ity
VTVM's.
A high- frequency crystal
-controlled
oscillator employing a p- channel
FET is
shown in
Fig. 12.
Gate bias
is
provided,
as
in
a
vacuum tube circuit, by
source
resistor
R2,
bypassed by C2.
The
feed-
back needed to start and sustain oscilla-
tion
is furnished by the
FET's inter -
electrode capacity
as well as
by stray
wiring capacities.
Figure 13
features a single p- channel
FET, Q1,
in
a modified Baxandall hi -fi
tone control circuit which can be used
as
part
of a stereo control center. Po-
tentiometer
R2
serves
as the
bass
con-
trol,
and R5
as the
treble
control.
Finally, a
simple preamp circuit using
an
IGFET (MOSFET,
or
MOST,
take
your
choice)
is
given
in Fig. 14. Here,
gate bias
is
provided
by
a
22-
megohm
resistor, R1,
returned
to the drain elec-
trode.
94
CI
0.1pç
INPUT
R2
!MEG.
C2
C3
.005pF
RI R3
p0K
120K
R5
500K
-22V
R4
50K
47K
300KK
G
2N2Q43
C6
O 0.IUF
Arlo
C4 C5 +
300 1000
pF
s
R7
2.2K
í22V
OUT
PUT
Fig. 13. Modified Baxandall
hi -fi
tone control
em-
ploys a single p-
channel FET (Siliconix 2N2843).
Separate
bass
and
treble controls
are provided.
INPUT
I
-20V
OUTPUT
1
Fig. 14.
Definitely
not
recommended
for
the ex-
perimenter, this
single -stage preamplifier
features
an
insulated -gate
field
-effect
transistor
(IGFET).
These
circuits
illustrate
a few
of the
many
practical
applications
of
the
FET.
They
are
not intended
for use
in
con-
struction
projects
as
shown, since
some
component
values might have to
be
changed
to compensate
for the use of
different
FET's.
In
any case,
only an
experienced
technician
should
attempt to
use
an
IGFET in
the
application shown
in
Fig. 14.
Practical
FET
projects will
be covered
in future issues.
One
thing
is
certain:
Mr. FET
is a
real
"comer," and should
have
a
bril-
liant
future! -30
POPULAR
ELECTRONICS
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