Dynaco FM 1 Owners Manual

Page 1

SERIAL NUMBER

dymaca

This number must be men-
tioned in all communications

T u N E R F M - 1 concerning this equipment.

Ln xv. ::::

ASSEMBLY
ALIGNMENT
OPERATION

Price $1.00

Nymca iNC. 3060 Jefferson St.. Philadelphia, Pa. 19121 U.S.A.

-OO' ' o,ao.com

Page 2

SPECIFICATIONS

BASED ON II'IPM STANDARD I-IOO

Unable Semitivltyx

SIgnal-te-Nolse latle:
Hal-monk Dletertlen:
Drltt:

Frequency Response:

Capture latlo:
Selectivity:
Audie Hum:

AM Suppresslent

4 microvolts for total noise and dis-
tortion 30 db below 100% modulation

70 db below 100% modulation level
less than 0.25% @ 100% modulation
less than 0.03%

$0.25 db 20cpeto20KC
3:0.5 db lOcpsto40KC

5 db

54 db

73 db below 1 volt output
greater than 63 db

ADDITIONAL SPECIFICATIONS

IM Dlstertlent

Audio Output:

Output Impedance:

Olsctlmlnator Peal: to
Peak Separation:

Antenna Input:

DlaI Callbratlon
Accuracy:

Power Consumption:

less than 0.5% from 10 microvolts to
100,000 microvolts @ 100% modulation

2 volts @ 100% modulation
less than 5000 ohms

greater than 900 KC

300 $2 balanced
75 12 unbalanced

0.2 (0
50 watts

Bob01605@aol.com

Page 4

The LP. Amplifiers and limiters

Phase shift in an FM signal corresponds to amplitude
non-linearity or distortion in an AM signal or in an audio
amplifier. Accordingly, the LE amplifier circuits were
designed for minimum phase shift across the pm band.
Since this occurs with undercoupled transformers, the
alignment of the I.F. section is greatly simplified. Simple
peak tuning (tuning for maximum signal) is the optimum
adjustment for the undercoupled I.F. transformers. This
minimum phase shift approach maintains low distortion
of the audio signal all the way down into the noise and
permits useful reception of weak signals even without full
limiting action.

A 6BA6 variable-mu pentode is used for the first and
second I.F. stages, and 6AU6 sharp-cutoff pentodes are
used for the succeeding two stages. Each LF. stage acts as
a limiter when the signal input to that stage reaches a
pre-determined point. Thus no automatic volume control
circuit is needed and no additional recovery time constants
exist to introduce delay on fading signals. There is suffi-
cient gain in the receiver so that the last limiter is effective
on input noise.

The Discs-initiator

A balanced-bridge discriminator configuration is used
in place of the conventional unbalanced circuit. This circuit
balances out any noise and signal rectification occurring
in the plate circuit of the last limiter tube and is the key
to the phenomenally low distortion figures achieved by the
Dynatuner. A wide band discriminator transformer is used
to obtain the full benefit of this design, and matched semi-
conductor diodes are used in place of vacuum tubes to
avoid heater hum at this critical point in the circuit.

The balancing action of this circuit reduces the inter-
channel noise (between stations) by a factor as great as
10 db in level over many conventional tuners which use
limiter-discriminator ciicuits.

The Audio Section

The first section of the 12AX7 dual triode is used as a
direct-coupled cathode follower between the discriminator
and the de-emphasis network. This prevents loading of the
high impedance discriminator circuit by the de-emphasis
network with its consequent reduction of high frequency
transient (square wave) response. A low impedance
de-emphasis network is used to feed the volume control
of the tuner directly. Also a multiplex take-off point is
provided at low impedance which will not affect the regular
operation of the tuner.

The second section of the 12AX7 is a feedback plate
follower audio amplifier compensated for the very wide-
band response inherent in the rest of the tuner circuitry.

"to Tuning Eye

In operation this eye acts as an indicator showing when
a station is tuned properly, and is connected through the
appropriate network to the last limiter grid circuit. During
a portion of the alignment prowdure, the eye is connected
to other specified parts of the circuit to indicate correct

alignment. This is the only instrument required during the
alignment procedure. The operating point of the eye has
been set for extremely precise indication of the optimum
tuning (or alignment) condition, and is a more accurate
indicator than tuning meters.

The action of the eye in tuning is very sensitive. It will
indicate a signal as low as 1 microvolt; it approaches
maximum closure at 10 microvoltsmyet it cannot be over-
lapped at higher signal strengths. The center of channel is
always indicated precisely. There is no flat spot in
tuning.

The Power Supply

The power supply is a conventional full wave pi"
rectifier using a 6V4IEZBO rectifier. Additional power
handling capability is included to power a Dynaco multiplex
adapter in the space provided on the chassis.

The Dynatuner is engineered to provide the finest
available overall performance. It is also designed to main-
tain this performance level for many years. Unlike other
tuners which must be factory aligned to give rated perform-
ance, the Dynatuner can be adjusted to. and kept at
optimum performance by its owner.

USING YOUR DYNATUNER

Your Dynatuner has been designed to give you the
highest quality of FM reception combined with permanence
of its excellent operating characteristics. A few moments
learning how to use it will amply repay you with increased
satisfaction.

The tuner must be connected to either a preamplifier or
directly to an amplifier using shielded cable of the type
supplied. It is acceptable to use cable lengths up to 25 feet
if the tuner is required to be located away from the associ-
ated equipment.

The audio cable can be plugged into either of the two
output sockets as normally wired. The second socket can
be used to connect to the other channel of a stereophonic
system or to a tape recorder, or it can be left unused.
Later, if you wish to add a Dynaco multiplex adapter, the
extra socket will be the output for the second stereo channel
by connecting it internally to the adapter, for which space
has been left on the chassis. The extra socket can also be
connected to the multiplex output of the tuner for use with
external adapters. See the Appendix for specific informa.
tion on this.

The front panel controls of the Dynatuner have been
made as simple to use as possible. The function of the
on-off switch is obvious. This switch also controls the AC
outlet on the rear of the tuner so that it is possible, if
desired, to turn both tuner and amplifier, for example, on
and off simultaneously. It is also possible when using the
Dynatuner with equipment which has additional switching
facility, such as the Dyna PAS-2, to leave the on-off switch
on" and use the auxiliary equipment for all the switching.

The tuning knob of the Dynatuner enables tuning from
one end of the FM band to the other. By observing the
tuning eye, it is simple to see precisely when a station is in

Bob01605@aol.com

Page 14

23( ) Remove the wire from the center ground pin of
socket V7.

24( ) Cut a piece of wire exactly 15/16" in length. Strip
exactly 'A " 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, to 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 of 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
correct orientation.

26( 3 Turn the tuning knob until you have located an
FM station of known frequency at the high end of
the band (close to 108 megacyclm). the higher the
better.

27( ) Adjust the oscillator trimmer capacitor CS through
the hole in the bottom plate. using a small screw-
driver. At the same time readjust the tuning knob
until the stations 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 stations 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 accurately, the dial readings will not
coincide with station frequencies across the dial.

29( ) 'lune accurately to a station near 108 megacycles
and adjust the two trimmer capacitors 01-8 and
01-0 on the tap 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 V4" open) or proper alignment will not
be realized.

BobO1605@aol.com

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
is very few microvolts) it will be noticed that the
eye is sensitive to flutter as a result 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 Cl-B and Cl-D.

30( ) 'lune carefully to a station near 88 megacycles and
adjust the two brass slugs in the mixer coil L3 and
the RF. coil Ll for maximum eye closing.

The last two adjustments should be repeated,
since there is interaction between adjustment of the
trimmer capacitors and the slugs of the coils. This
adjustment of L] and L3 is not critical, and may be
a broad peak, necessitating an approximate center
setting.

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 DIFFICUIJY

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 OS, 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-ot'f switch, and power
transformer primary winding are all properly connected
into the circuit.

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