Dynatuner FM-1 Instrucciones de montaje Operación de alineación - Página 15

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23(

Remove the wire from the center ground pm of

socket V7.

24( ) Cut a piece of wire exactly 15/16" in length. Strip

exactly

of insulation from one end. The other end

need not be stripped. Insert the stripped end

fully

into the bottom of eyelet #29 (S). This wire should

stand up straight from the PC-8 board with the

other end free,

a height of 11 /16". Dress adjacent

wires away to permit this wire to stand straight

without touching any others.

This wire may seem to be unusual, as it is con-

nected at one end only. However, it is what is known

in electronic parlance as a "gimmick" and it is

actually a small capacitor which corrects for the

effects of interaction between the adjustments of the

two slugs in the discriminator transformer. At such

time as realignment is performed, this "gimmick"

should be removed before aligning the discriminator.

Alignment 01 the Front End

The oscillator must now be adjusted. In this sec-

tion, dial tracking will be simplified if another FM

radio is available to enable you to identify stations

readily.

25(.,;(Place the bottom plate on the tuner. See that the

side holes are aligned with the chassis holes, for

/on'ect orientation.

26(0 Turn the tuning knob until you have located an

FM station of known frequency at the high end of

the band (close to 108 megacycles), the higher the

better.

27( ) Adjust the oscillator trimmer capacitor C8 through

the hole in the bottom plate, using a small screw-

driver.

At the same time readjust the tuning knob

until the station's frequency is indicated in the

plastic window by the tuning dial. In other words,

you set the dial to show the correct frequency and

adjust the trimmer capacitor until the eye closes to a

maxImum.

28( ) Now find a station of known frequency at the lowest

end of the dial (close to 88 megacycles). Using a

small screwdriver, and touching only the insulated

handle. adjust the brass slug in the oscillator coil L4

while setting the tuning dial to the station's broad-

cast frequency. This is the same type of adjustment

as was made in the preceding step.

It may be necessary to repeat the adjustments at

the two extremes of the dial several times in order to

have the tuner "track" properly. If the adjustments

are not made accurat=ly, the dial readings will not

coincide with station frequencies across the dial.

29i ) Tune accurately to a station near 108 megacycles

and adjust the two trimmer capacitors C1-B and

C l-D on the top of the tuning capacitor. The screw-

driver should not touch the capacitor shield when

making these adjustments. The adjustment should

be made for maximum eye closing. If the eye is

closed to its normal maximum, the effects of these

adjustments will not be readily apparent, so it is

essential that a weak signal be used here (where the

eye is about

II,"

open) or proper alignment will not

be realized.

To obtain a sufficiently weak signal, it may be

necessary to remove the antenna and substitute a

short piece of wire. Shorting out half the antenna is

another alternative. With signals of this magnitude

(a very few microvolts) it will be noticed that the

eye is sensitive to flutter as a !"esult of airplanes

passing overhead, or varying signal strength as a

result of atmospheric conditions. Care must be

taken not to allow this sensitivity to influence the

actual adjustment of C1-B and CloD.

30( ) Tune carefully to a station near 88 megacycles and

adjust the two brass slugs in the mixer coil L3 and

the R.F. coil L1 for maximum eye closing.

The last two adjustments should be repeated,

since there is interaction between adjustment of the

trimmer capacitOl's and the slugs of the coils. This

adjustment of L1 and L3 is not critical, and may be

a broad peak, necessitating an approximate center

setting.

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This completes the alignment of your Dynatuner.

No further alignment should be required unless

there is a change in tubes or components. At that

time, you have the means of re-aligning it so that

your Dynatuner will always be at the very peak of

its performance capability. However, one word of

caution is in order-do not make these adjustments

unnecessarily, as the various slugs will eventually

loosen and cause tuning shifts to the detriment of

performance. Alignment adjustments should be con-

sidered as a semi-permanent type of adjustment,

and not an operational adjustment.

After completion of alignment, install the rubber

feet in the corner holes of the bottom plate, and

secure the bottom plate and the cover with the four

sheet metal screws. The flange on the front of the

cover goes between the steel front panel and the

brass front plate.

Your Dynatuner is now ready for long pleasureable

use.

IN CASE OF DIFFICULTY

In the event that your first attempt at listening to your

Dynatuner is unsuccessful, a systematic approach to locat-

ing the difficulty will save you much time and trouble.

Because 90% of the difficulties which are encountered

can be attributed to either incorrect wiring or a poor solder

connection, it is strongly recommended that you first ask

someone else to check the wiring against the pictorial

diagrams. as frequently one person will make the same

error twice.

Drift, or shifting of the tuned signal frequency, should be

cause to suspect poor mounting or soldering of C7 or C8, or

a defective 6AT8A tube.

If the dial light and tubes do not light when the set is

plugged in and turned on, check to see if the fuse is all

right. A continuity test at the prongs of the line cord with

a meter will show if the fuse, on-off switch, and power

transformer primary winding are all properly connected

into the circuit.