Static Tests - Elenco Electronics AM/FM-108TK Manual

SECTION 8
FIRST FM IF AMPLIFIER
The operation of
the first lF amplifier
is
the same
as
the
second lF amplifier except that the gain
is different.
The
gain is set by the AC impedance of the primary side of
iZ
and the current in
Q4.
The current in Q4 is set
by
the resistors R12, R13 and R15. Capacitors C14 and
C15 bypass the AC
signalto ground. C13 and C16 are
bypass capacitors from
V+
to
ground
to
prevent
feedback
on the V+
line.
R19
is
used
to
widen the
bandwidth of the transformer T2.
ASSEMBLY INSTRUCTIONS
tr
R12
-
10kO Resistor
.'
.(brown-black-orangegold)
n
R13 -
47k() ne$istor
,,,,(yellow.violef
oranQe:gofd)
n
R14:. 10k0
Resietor
.
(b-rown.black.oqan
ge.gotd)
n TP11 'Test Point Pin
,,,
,,
'
,'
,
{see
Fiqure
A}
o 94 ..
2N3904 Transigtor
n C16:
.01rrF DisCaP'{103)
il
C15:
.01pF Discap
{103}
STATIC TESTS
Q4 BIAS
Connect your VOM
as
shown
in
Figure
37.
Turn the
power
ON.
The voltage
at the
base
of Q4
should
approximately
be
1.4
volts. lf
you
do not get
this
reading, check R12, R13,
Rl5,
Q4 and
T1
.
Figure
37
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