Dynaco FM3 Tuner Amplifier Schematic

Page 3

This completes the assembly of your Dynatuner. You
should now make one final inspection of the unit to see
that all connections are soldered. One poor solder connec-
tion can upset the performance of your tuner, or prevent
proper alignment. Be sure that there are no loose wire
clippings.,or pieces of solder, and that there are no bridges
of solder across insulated areas of the circuit boards.

Check to be sure that the position of the wires in your
tuner agrees closely with the pictorial diagrams and with
the photographs. The diagrams must sometimes be exag-
gerated for clarity, but any discrepancies between them and
the photographs are of no consequence.

Insert the tubes into their sockets and install the dial
lamp and the fuse. Install the tube shields, making sure
that the ground strap of each socket slips between the tube
and the shield. The larger shields go on the 9 pin tubes, and
the smaller ones on the 7 pin tubes. V8 and V9 do not
use shields.

There are two small brass~plated self-tapping serews
which will be used to secure the aluminum front plate to
the front panel. To avoid scratching the front plate, it is
wise at this point to cut their threads into the holes above
and below the tuning capacitor shaft by inserting these
screws part of the way, and removing them. This will
enable much easier insertion when the front plate is
installed.

Remove the % nut holding the volume control in posi-
tion. Insert the rectangular plastic insert into the front
plate cutout from the rear. The top edge is narrower than
the. bottom. Place the front plate against the steel front
panel so that the plastic insert is held between the two
plates. Install the 3/3 nut on the volume control shaft and
tighten it. Now install the two small brass self-tapping
screws above and below the tuning shaft. Rotate the volume
control shaft fully counter-clockwise and install the small
knob with the pointer at the 7 oclock position. Install the
large knob on the tuning shaft, and tighten the set screws
of both knobs.

Install the rubber feet in the corner holes of the bottom
plate by inserting a #8 screw in the. recess of each foot,
and secure each with a nut on the inside of the bottom
plate. Secure the bottom plate and cover with the tour
sheet metal screws. The flange on the front of the cover
slides between the steel front panel and the aluminum front
plate. Care should be exercised when handling the unit,
for the gold anodized panel and knobs will not withstand
undue abuse.

Now plug the Dynatuner in (to AC current sources
only) and turn it on. Allow it to operate for an hour or
more to allow the tubes to age and for operating conditions
to stabilize before proceeding with alignment. During this
time you should be able to enjoy reception from local
stations.

ALIGNING YOUR DYNATUNER

The Dynatuner is unique in its simplicity of alignment.
Every stage can be aligned using the dual beam tuning eye
as an indicating instrument, and this alignment is as pre-
cise as can be accomplished with the most complex labora-
tory equipment. The ability to achieve this measure of
accuracy without external test equipment is a Dynatuner
exclusive, and the indicating accuracy of the tuning eye
circuit surpasses that of any comparable meter system.

16

It is important to emphasize that when this procedure
has been carefully followed. it. is not possible to improve
on this alignment, and the Dynatuner will meet the most
rigorous performance standards. It is essential that any
servicemen who works on this tuner be informed of this
procedure, and that he is also advised that conventional
sweep alignment techniques are not considered either
satisfactory or desirable.

It should be understood that successful alignment is
dependent on a properly constructed tuner. A wiring error
or a poor solder connection could prevent satisfactory com-
pletion of some steps, or could cause erroneoue, settings to
the extent that additional test equipment might then be
required to reestablish the proper Operating conditions fer
realignment. Certain parts of the Dynatuncr have been
preset close to the proper operating point. These include
the LP. transformers, the discriminator transformer, the
multiplex transformers, and the slug-tuned coils on the
PG? board.

The cover and bottom plate must be removed for align-
ment. The complete stability of the Dynatuner allows pre-
cise alignment without special shielding. Before proceed-
ing with alignment, three approximate adjustments should
he made, which will permit reception of local stations dur-
ing the hour of operation while tube conditions stabilize.
A similar aging period should he allowed before realign-
ment following any tube replacement on PC-7 and lJC-S.

On top of the tuning capacitor Cl there are two adjust-
ment screws (trimmer capacitors) accessible through the
two holes in the top of the shield. The center screw [Cl-D)
adjusts the mixer, and the rear screw Cl-B adjusts the RF.
stage. The approximate settings given in steps #1 and #2
below have already been made as the capacitor is supplied
to you.

ll .J Turn in the screw Cl-n on the center (mixer) sec-
tion until it is in all the way. it should be snug,
but do not force it. Then back it off 1:1 turn counter-
clockwise.

2l 2) Turn in the screw 01-3 on the rear lRF.) section
until it is in fully, but do not force it. Then back it

off a turn counter-clockw isc.

3( J The oscillator trimmer capacitor CH screw (ac-Cos
sible from below the chassis) should be turned until
the head of the screw is he from the triangular nut.

With an antenna attached, and with the tuner connected
to an amplifier and a speaker, turn the tuner on. The dial
lamp should light, and there should be a slight glow visible
in each tube, and then the tuning eye should glow. All of
this should take only about 15 seconds. When turning the
tuning knob, some deflection of the lower beam of the tun-
ing eye should be apparent as the tuning passes the fre-
quencies of local stations. At higher settings of the volume
control, it should be possible to hear some hiss between
stations and sound from the stronger stations. If all of these
effects cannot be obtained, refer to the section In Case of
Difficulty before attempting to use the tuner further or to
align it.

Two tools are necessary for alignment: a small tipped
screwdriver with an insulated handle, and a plastic tool
(supplied) which has a hexagonal end for adjustment of
the tuning slugs in the LR, discriminator and multiplex
transformers. Only the plastic too] should be used to adjust