Heathkit AR-14 - Page 69

Page 62
CHANNEL SEPARATION TESTS
If an FM stereo generator is available, this
generator may be used to check channel separa-
tion. To check separation, coil L7 and transform-
er T7 must be adjusted as outlined in the follow-
ing steps.
Equipment needed: FM stereo generator andAC
VTVM. If desired, an oscilloscope may also be
used.
( ) Disconnect the negative (-) lead of capacitor
C39 from the circuit board at point R.
( ) Connect the FM stereo generator output
lead to the negative (-) lead of capacitor
c200.
( ) Connect the AC VTVM (and oscilloscope if
desired) to the RIGHT TAPE OUTPUT
socket of the Receiver.
Set the SOURCE switch on the Receiver to
the @ FM position.
( ) Set the FM stereo generator to the right
channel output and use the 19 kc pilot signal
with a 1 kc multiplex signal.
( ) Adjust coil L7 for maximum brilliance of
the stereo indicator lamp.
( ) Pull out the PHASE switch, then adjust the
PHASE control fully clockwise.
NOTE: Complete the following adjustments very
carefully to obtain good stereo listening.
( ) Adjust transformer T7 as follows:
1.
Turn the slug (not more than one turn
in either direction) until the sound out-
put is clear.
2. Turn the slug counterclockwise to the
point where the sound output just starts
to become garbled. Note the position
of the flag on the alignment tool.
I
- ~ --- --
-- ------ -
~ff·&iffH!l
3. Turn the slug clockwise 1/ 4 turn,
( )
Readjust coil L7 until a null or minimum
sound output is obtained. NOTE: If there
are two nulls, use the null adjustment that
is closer to the top of the coil. The proper
adjustment should be close to the point of
maximum brightness of the stereo indicator
lamp.
( ) Turn the PHASE control counterclockwise
for a maximum output reading, then push the
PHASE switch in.
( ) Note the output reading on the VTVM. Then
change the FM stereo generator to the left
channel output and note the VTVM output
reading for this position. The difference
between the two output readings is the right
channel separation, usually expressed in
db
(decibels).
( ) Disconnect the VTVM (and oscilloscope if
used) from the RIGHT TAPE OUTPUT
socket and connect it to the LEFT TAPE
OUTPUT socket of the Receiver.
( ) Turn the channel switch of the FM stereo
generator to the right channel position, then
to the left channel position. Note the output
reading on the VTVM for each position. The
left channel separation is the difference be-
tween these two readings.
( ) Disconnect the FM stereo generator, AC
VTVM, and oscilloscope (if used) from the
Receiver.
( ) Reconnect the negative lead of capacitor
C39 to the circuit board at point R; then
resolder the connection.
This completes the Channel Separation Tests.