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Alignment Procedures
43
1
.
6
Mc/s Band-pass Filter
50. To carry out alignment of this filter, the mixer chassis must first be removed. After
the removal of the chassis, turn the receiver on to its side and reconnect, from the
underside, the two leads (6.3V and 200V H.T.) to their respective pins.
51. Remove all the valves on the chassis except the third mixer V25. Connect a suitable
valve voltmeter, shunted to 7pF, to pin 7 of V26. Inject an accurate 1.6 Mc/s signal
at socket SKT301 (pink). A large input from the generator should be used initially
and reduced as necessary throughout the alignment. Adjust cores L306 and L309 in
the first I.F. transformer and cores L313, L314 in the second I.F. transformer for a
maximum reading on the valve voltmeter.
52. Check the gain of the I.F. amplifier as follows:-
(1) Connect the signal generator to SKT301 of V25. For an input of 125mV, an
output of not less than 500mV should appear at pin 7 of V26.
(2) Check that the 13 kc/s bandwidth is obtained with not more than 2dB fall in
output and that the response curve is reasonably symmetrical.
(3) Refit valves and mixer chassis.
2 – 3 Mc/s Band-pass Filter
53. This filter is pre-aligned and should not require further adjustment. If the performance
of the receiver has deteriorated and the filter is suspected, it should be returned to
the factory to re-adjustment.
1.7 MC/S OSCILLATOR/AMPLIFIER
54. With a valve voltmeter connected to SKT306, adjust the core of L330 for maximum
meter indication.
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