Heathkit SB-401 - NEUTRALIZING; FINAL BIAS

Page
94
Gg
HearHKiT
NEUTRALIZING
(S-1).
Bend
the
lead
of
the
capacitor
care-
fully
to
prevent
breaking
the
ceramic
form,
(
)
Rotate
the
BAND
switch
to
28,5,
(
( ) On the bottom of the chassis, connect a
Place the VTVM RF probe in the ANTENNA 680 2 (blue-gray-brown) resistor from lug
connector, 3 of terminal strip P (S-3) to the center
of the bare wire connected between lugs 3
of tube sockets V10 and V11 (S-1),
—
( ) Set the FUNCTION switch to TRCV,
{ ) Rotate the LEVEL control fully clockwise, Refer to Figure 2-4 (fold-out from this Page)
for the following steps,
Key the tra itter,
Ga
Bey
a
ed
(
)
Install
the
final
amplifier
rear
plate
on
th
\
!
final amplifier enclosure, using #6 x 3/8
/
é
(
)
Adjust
the
DRIVER
control
for
a
maximum
sheet
metal
screws,
indication
on
the
VTVM,
;
‘
(
)
Install
the
final
amplifier
top
plate
oy
the
(
)
Adjust
the
FINAL
control
for
a
maximum
final
amplifier
enclosure,
using
#6
x
3/8"
indication on the VTVM, with the LOAD con-
trol set at the 50 2 position,
sheet metal screws,
( ) Using an insulated screwdriver, adjust the IMPORTANT: Do not key the Transmitter fo
Neutralizing Capacitor for a minimum in- more than 30 seconds at a time until after you
dication on the VTVM, have completed the Final Transmitter Adjust-
ments,
_—
~
Readjust the FINAL control for maximum
indication on the VTVM,
FINAL BIAS
( ) Readjust the Neutralizing Capacitor for a
minimum indication on the VTVM, ( ) Connect the dummy load to the ANTENNA
tivoru connector, Do not use a light bulb as a
( ) Turn the FUNCTION switch to the OFF dummy load,
position,
-_
~
Plug in the Transmitter line cord,
-_
~~
Unplug the Transmitter line cord,
Remove the 6CL6 driver tube (V9).
—
Disconnect the VTVM RF probe from the (
—
~
Transmitter,
( ) Set the METER switch to PLATE,
CAUTION: Be sure to use an insulated handle
screwdriver
in
the
next
step
to
discharge
the
(_)
Place
the
BAND
switches
in
the
3.5
position.
high voltage capacitors,
Turn the FUNCTION switch to TRCV,
-_
—
( ) Discharge the high voltage capacitors by shorting the .
lower lead of feedthrough capacitor Q to the chassis Turn the MODE switch to USB. ;
with the blade of a screwdriver. Be sure to touch the
metal blade of the screwdriver to the chassis first, then
to the capacitor lead. Repeat this step several times to
be sure the capacitors are completely discharged. (
— we
Allow a few minutes warmup time,
—
Key the Transmitter by pushing the PTT button on the
microphone or by shorting lug 2 of the microphone
connector to the chassis with a screwdriver blade. Then
adjust the BIAS ADJUST control for a 50 ma
indication on the meter of the Transmitter. Refer to
(
)
On
top
of
the
chassis,
connect
the
lead
of
Figure
5-1
on
Page
108
for
the
explanation
of
the
|}
feedthrough
capacitor
Q
to
lug
2
of
coil
TB
meter
scales.
Refer to Figure 2-3 (fold-out from this Page)
for the following steps.