BUSH
Dismantling:
Place the cabinet face downwards, remove the detachable
base, then remove the battery. Separate the two halves of the cabinet by
releasing the two fasteners contained within the mouldings, then lift the back
section clear.
(Note:
Dismantling to this stage will permit the R.F. align
ment procedure to be carried out.) Unscrew the two
4BA
nuts retaining the
chassis to the speaker pillars, then loosen the two self-tapping screws securing
the top edge of the chassis to the die-cast lugs of the top assembly. Lift out
the chassis, unsoldering the loudspeaker leads if required. Replace the
chassis by reversing the above procedure.
Replacement of Drive Cord:
Note:
About 36 in. of Terylene cord will
be required for the new assembly. Remove the chassis from the cabinet as
described in the dismantling procedure above. Carefully ease the scale
pointer from its carrier then remove the four Phillips head screws securing
the scale plate to the chassis. Lift the plate clear. Withdraw the circlip
located on the end of the tuning spindle, then loosen the grubscrews securing
the capstan to the spindle and withdraw the tuning spindle complete with
knob. Lift the capstan clear, noting the position of the nylon bearing to
ensure its correct replacement. Set the tuning capacitor so that the vanes
are approximately half meshed. Now from a point half-way along the
new length of cord, make a loop of one turn round the spigot contained
within the drive drum, passing the cord ends out through the slots in the
drum. Assemble the cord drive and then refit the capstan. Finally pass
the ends of the cord through the eyelet, knotting them under tension from
the spring-loaded pulley mounted above the Off/On volume control.
Note:
When refitting the scale pointer, ensure that it registers with the
datum marks on the right of the scale when the tuning capacitor is fully
meshed.
Adjustment of RV3:
The replacement of components in the output
stage may necessitate the resetting of RV3. This may be done by setting an
AVO model 8 to the 50 /LA. D.C. range, and connecting it across R30,
observe correct polarity. With the volume control set to minimum, adjust
RV3 in accordance with the table below:
Ambient temp.
°C
OF
18
65
23
73
28
82
33
91
Meter reading
(50 /-,A. f.s.d.
9'24
1l'08
12·8
15'04
Equivalent
I. in mA. of
mV.
(across R30)
output pair
23'1
7'0
27'72
8'4
32'01
9'7
37.62
11'4
Alignment Procedure:
Equipment required: An A.M. signal generator
to cover 158-1605 kc/so An output wattmeter with a range 0-1 watt to
match 15 ohms impedance. A non-metallic trimming tool for adjusting the
iron cores and R.F. trimmers. A 10-pF. capacitor for injecting R.F.
107