Jackson Bell Co., Ltd. 28 Schematic

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Manufacturer:Jackson Bell Co., Ltd.

Schematics Content:

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Page 1:


Service NotesY


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Alignment Data.


Make all adjustments with volume control at maximum.

To align 175 K0 I.'F. stage -
Set switch in broadcast position and short out middle, or oscillator section of
variable condenser. Apply 175 K0 modulated signel'to front section of variable
condenser or grid cap. Chassis must be grounded to 175 K0 oscillator. Remove
27 and 24 short-#wave tube beside LF. transformer and adjust all LF. trimers
to maximum output. This should be checked by an output meter.

To align Broadcast Bend.
Close variable condenser and set dial at last division mrker past 550 KC. Open
variable condenser to 1550 KC and with 1550 KC modulated oscillator signal.
Adjust middle or oscillator section trimmer of variable condenser tc maximum
response. RJ. and antenna section of trimmers are adjusted likewise at this
frequency. Signal generator at 850 K0. Set dial at 850 KC and resonate by bending
of slit plites on variable condenser. Repeat above at 650 KC and 550 KC.

To align 84:0 K0 Short-wave LF.
Place the type 24 and 27 shortwave tubes back in the chassis, and after `they have
warmed up, turn wave selector, short-wave, to any one of the short-#wave positions.
Connect output of 840 KC modulated signal generator tc grid cap of short-wave 24
tube. Notez- When short-wave is in short-wave position the variable condenser no
longer tunes the broadcast coils. These are tuned to 840 K0 by means of large
trimmer condensers, adjusted from top of chassis beside variable condenser. Each
840 KC trimmer is beside the section of the variable condenser which it substitutes
for. Note :v In location where a broadcast station is on or too close to 840 KC,
adjust above cr below if interference is encountered.

To aligz short-'wave oscillator and modulator.

Hotea- In the short-weve bands the front and rear of the variable tuning condenser,
are connected in series with semi-variable padding eondensers. These reduce the
effective tuning cap of the tuning condenser to the low value necessary for tuning
the short-wave coils.

In the absence of the short-wave signal generator, the broadcast signal gen-
erator may be set to 1000 KC. This will give harmonics on short-wave at 150 Meters,
100, 75, 60, 50, 42.8, 37.5, 53.5 and 30 meters. The best harmonic to use is the
'I5 meter one as it is just below the amateur 85 meters phone band.

Lift front of chassis up until set lays on its back. Three trimmer ccndensers
will be seen in upper left hand corner of chassis. These are reading from top to
bottom. The short-wave oscillator padder (in series with front section of tuning
condenser). The short-wave modulator padder (in series with the rear section of
tuning condenser), and last the trimmer tuning the modulator plate choice to 840 KC. \

With the wave selector short-wave in 40 to 80 meters position and signal gen-
erator at 1000 KC. Adjust the top or short-'wave oscillator padding condenser until
the harmonics appear in their proper places at '75, 60 and 50 meters. Nortez- Disre-
gard weaker intermediate harmonics. Then adjust the short-wave modulator pedder
for m.th response. Notex- Tho tuning condenser must be swung back and forth
across the signal when this is being done as it effects the oscillator tuning. The
tuned choke trimusr is then packed on any signal.

The harmonics in the 20-40 meter band will be only approximately correct be-
cause of extremly high frequencies involved. However, they will be within one
meter correct on this bend.

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