Dynaco FM 3 Owners Manual

Page 1

SERIAL NUMBER

STE R E0 M ATIc This number must be men-
tioned in all communica-
M u LT I P L E x Hons concerning Dynakit.

MODEL FM-3

ENS?E§%£§§E§§§@N$ Frill???

ASSEMBLY
ALIGNMENT
OPERATION

Price 39/. 00

126416

DYNA COMPANY my: :2:::::::.1°",.f:::

Bob01605@aol.com

Page 2

-: "Qparating Instruotwns . t . ., .'
"Teghnical Description . I .......... _
~ , IJVGeneraI wilting Practice ._ ._ ...... 3. ; .., . .,

A I Assemblyklnstmctions I . t, .

AIignmemt- Ifistructians ;

Z 1240 Volt Power Transformer ..... ,.
In Case of Difficulty » _
Stamina and Warranty . . ._ ........
How to Make a Fouled Dipole Antenna
_FartsList,..x.y..~,.,.-.,..l....L.y

__Voltage, Check Pnjnts '.. . . . .s. . .

CDNTENTS

SPECIFICATIONS

BASED ON

Useable SansltIvlty:

Signal-to-Nolsa Ratio:
Harmonlc Distortlon:
Drift:

Frequency Response:
Capture Ratlo:
Selectlvlty:

Audio Hum:

AM Suppression:

IHF STANDARD T-IOO

4 microvolts for total noise and distortion
30 db below 100% modulation

70 db (q; 100% modulation

less than 0.25% Q1; 100% modulation
less than 003%

:I: 0.5 db 10 cps to 15 KC

5 db

54 db

73 db below 1 volt output

greater than 63 db

ADDITIONAL SPECIFICATIONS

IM Dlstortlon:

Audla Output:
Output Impedance:

Dlscrlminator Peak to
Peak Separatlon:

Antenna Input:

Dlal Calibration Accuracy:

Power Consumption:

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

2 volts (47 100% modulation
less than 5000 ohms

greater than 900 KC

300 Q balanced
75 Q unbalanced

0.2 %
55 watts

STEREOPHONIC PERFORMANCE

Unable Sencltivlty:

IM or Harmonic Dlstartlon:

Separation:

3 db less than mono mode

less than 1 % (including 19 KC and 38 KC
residual)

80 db

Bob01605@aol.com

Page 5

2. An oscillator-mixer stage using a 6AT8A high con
version triode-pentode with screen injection.

3. Four I.F. amplifier stages with progressive limiting
using two 6BA6 pentodes and two 6AU6 pentodes.

4. A symmetrical wide band discriminator with matched
semi-conductor diodes.

5. A cathode follower providing discriminator isolation
and low impedance source to the multiplex and audio
channels using one~half of a 12AX7/ECC-83.

6. A feedback audio amplifier using one-half of a
12AX7/ECC-88.

7. A 19KC amplifier and doubler using a pentode-triode
6BL8/ECF-80.

8. A balanced bridge synchronous detector using four
matched semi-conductor diodes.

9. Stereo audio output stages consisting of feedback plate
followers using a 12AX7/BOOBS.

10. A dual indicator EMM»801 acts as a tuning eye and
as a stereo indicator.

11. The power supply, which uses a 6V4/EZ-80 full wave
rectifier.

The Antenna Circuit

Provision is made to match either a 75 ohm unbalanced
or a 300 ohm balanced transmission line, thus accommo-
dating any standard antenna array used for FM reception.

The R.F. Stage

The cathode coupled dual triode RF. amplifier circuit
was chosen for the input stage. It combines the high gain
and low noise figures of the commonly used grounded grid
input with a tuneable input~a necessary feature to pre»
vent overloading from strong signals which might cause
cross»modulation and spurious responses.

The Oscillator-Mixer

The triode section of the 6AT8A is used in a tickler
feedbac tuned grid oscillator circuit. Careful temperature
stabilization and choice of operating parameters result in
an oscillator circuit with sufficient stability to obviate any
need for automatic frequency control with its inherent
degradation of the audio signal.

The pentode section of the 6AT8A is used as the mixer.
The oscillator is injected into the screen circuit to provide
complete isolation of the oscillator tuning circuit from the
signal tuning circuit at the mixer grid. Oscillator drag
(change in oscillator frequency as themixer tuning is ad-
justed) is virtually nonexistent, greatly simplifying the
adjustment and tracking of the front end. This isolation
also reduces ire-radiation of the. oscillator energy into the
antenna which might cause interference in other nearby
receivers and television sets.

Circuit constants of the oscillator and mixer circuits
have been adjusted to give uniform sensitivity over the
entire FM band.

The M7. 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 LF. amplifier circuits were de-
signed for minimum phase shift across the pass 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

Bob01605@aol.com

the audio signal all the way down into the noise and per-
mits useful reception of weak signals even without full
limiting action.

A 6BA6 variable-ma pentode is used for the first and
second LF. stages, and 6AU6 sharp-cutoff pentodes are
used for the succeeding two stages. Each I.F. stage acts as
a limiter when the signal input to that stage reaches a pre»
determined point. Thus no automatic volume control cir~
cuit 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 Discriminafor

A symmetrical 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 and
matched semi-conductor diodes are used to obtain the full
benefit of this design.

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
limiterdiscriminator circuits.

The discriminator signal goes first through one-half of a
12AX7 functioning as a cathode follower and then through
the second half of this stage which is used as an audio
amplifier with plate to grid feedback. The output of the
cathode follower also is used as a source to a portion of
the multiplex circuitry.

The Multiplex Integrator

The first portion of the multiplex section is fed from the
cathode follower. This signal is Q-multiplied and amplified
at 19KC in the pentode half of the GBLS. Then it is
further amplified and doubled to 38KC in the triode sec-
tion of this tube. This triode section also acts as a limiter,
holding a constant 38KC level regardless of signal strength
and pilot amplitude. Such limiting greatly reduces noise
through the stereo gates and preserves equally good
separation at all level signals.

The audio signal from the plate circuit of the 12AX7 is
shaped in a 67KC band reject filter. Then it is mixed with
the reconstructed 38KC signal in a balanced transformer.
A four-diode bridge provides synchronous detection of left
and right channels which then are passed through a com-
bined 38KC rejection filter and audio de-emphasis network.

A signal from the 19KC amplifier section is used to acti»
vate the upper beam of the EMM~801 tuning eye which
illuminates the word STEREO when there is a stereo trans~
mission.

The action of the multiplex section is automatic as the
38KC channel is quenched in the absence of a pilot signal
from the broadcast station. However, it can also be shifted
to locked mono reception by use of the push~pull Stereo-
matic~mono switch which can deactivate the automatic
stereo feature.

The Audio Section

A 12AX7 is used for audio output, with one half for each
stereo channel. This tube has plate~to~grid feedback and is
used as a plate follower. It has low impedance output, per-
mitting up to 25 feet of shielded cable, It has very low
distortion and minimum frequency discrimination.

En

Page 10

1(

2(

3<

4(
5(

6(

7(

8(

9(

10(

10

CHASSIS ASSEMBLY

) Install the on-otf switch inside the front flange of
the chassis, noting the position of the lugs in the
pictorial diagram, Use two #4 (smallest nickel-
plated) screws. Lockwashers and nuts are not neca
essary as the holes in the switch are threaded.

) Install the three screw terminal strip with two sets
of #4 hardware. The screws go through the strip
first, which is mounted on the outside of the rear
flange of the chassis, Refer to the pictorial for
proper orientation of the lugs. Secure it with a lock-
washer under each nut.

) Insert the fuse holder into the special D shaped
hole. Note the orientation of the lugs. The rubber
washer fits between the shoulder and the outside

-of the chassis. Fasten in place securely with its
lockwasher and nut, but do not tighten excessively.

) Install the AC outlet with two sets of #4 hardware.

) Install the two audio output sockets on the inside
of the chassis using two sets of #4 hardware for
each. Note the orientation of the ground (short)
lugs in the pictorial.

) Install one of the two nine pin sockets which have
mounting flanges, in the center of the chassis. Note
the location of the blank space between the pins in
the pictorial. The socket is mounted on top of the
chassis with two sets of #4 hardware.

) Install the 3 rubber grommets. The larger one is
inserted into the line cord hole at the rear of the
chassis, and the other two are fitted into the holes
in the dividing partition in the middle of the chassis.

) Hold the PC-7 board as shown in the pictorial, with
the LR transformer away from you, and carefully
pick up the tuning capacitor C1, holding it so that
the shaft points away from you. Be particularly
careful that you do not touch the semicircular cop
per and aluminum colored plates of the capacitor.
If these are bent, even slightly, it will be difficult
to get the tuner to track accurately across the dial
when you come to the alignment procedure. Now
insert the small tabs which protrude from the bot-
tom of Cl into the corresponding five holes in the
top of PC-7. Be careful capacitor C7 is not dam-
aged. This fit is especially snug, but be sure that
the tuning capacitor is fully seated against the
board. Two of the threaded studs of the capacitor
will also engage the board, The shoulders of these
studs should seat against the board.

) Mount the PC»77C1 assembly on the top of the
chassis, locating it by the four threaded studs of
Cl. Install four sets of #6 (medium size) lock-
washers and nuts on these studs but do not tighten
them.

) Fasten the PC-7 board in place with five sets of
#4 (smallest size nickel plated) hardware. Install
the screws from the top, and secure with a lock-
washer under each nut. Tighten these, and also
tighten the nuts on the capacitor studs.

11(

12(

13(

l4(

15(

) Install the tuning capacitor shield, using three sets
of #4 hardware. Make sure that capacitors CG and
C7 do not touch the shield. The tab of the shield
is fed through the hole in PC-7 for the mounting
tab of T1. Solder both of these tabs to the board.
Be certain that no bare leads contact the shield.

) Install the LE circuit board PC-S on the top of the
chassis. Fasten with eight sets of #4 hardware.

) Install the multiplex circuit board PC-12 on top of
the chassis using four sets of #4 hardware. Follow
the orientation in the pictorial diagram.

) Feed all the power transformer (PA~509 or PB-012)
leads through the one-half inch hole as shown in
pictorial. Position the five lug terminal strip over
the power transformer mounting hole in the chassis
between the hole for the transformer leads and the
nine pin tube socket. Note the orientation of the
lugs in the pictorial. Fasten this corner of the
transformer and the terminal strip with #8 hard
ware (the largest size). Use #8 hardware to fasten
the remaining three corners of the transformer to the
chassis. Be sure all transformer mounting bolts are
tight, and recheck all other hardware to make sure
that all components are securely in place.

) Mount the filter capacitor C32 in the center of the
chassis. Note the identifying marks at each lug of
the capacitor (semi-circle, square, triangle, and
blank) and orient the capacitor according to the
pictorial diagram. Fasten it rigidly in position by
twisting the four mounting lugs 14 turn with a pair
of pliers.

WIRING THE FRONT PANEL SUB-ASSEMBLY

Unless otherwise specified, the insulation should be
stripped from each length of wire for a distance of 1A at
each end prior to installation.

1(

2(

3(

4(

5(

> Mount the tuning eye socket V8 (with mounting
flange) on the front panel with two sets of #4
hardware. Note that it is installed with the blank
space between pins #1 and #9 at the top of the
panel. The mounting flange is flush with the bracket
if the socket is mounted correctly.

) Strip the insulation back 1/2 from one end of a 2%
black wire. Remove the normal 1A, of insulation
from the other end. Feed the 1/2 bare end through
pin #3 of socket V8 and connect it to pin #1.
Keep it clear of pin #2. Solder pins #1 and
#3. Position this wire under the right»angle mount-
ing bracket for V8 and close to the front panel.

) Connect one end of an 81/2 red wire to pin #6 of
socket V8 (S).

) Connect one end of an 8 green wire to pin #7 of
V8 (S).

) Place the 5% lockwasher on the shaft of the volume
control assembly and mount the assembly in the
front panel. Locate the lugs as shown in the pic-
torial diagram. Fasten with the 3/3 nut.

Page 14

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 screws
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 % 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 #6 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 four
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
seruiceman 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 tuneri A wiring error
or a poor solder connection could prevent satisfactory com-
pletion of some steps, or could cause erroneous settings to
the extent that additional test equipment might then be
required to reestablish the proper operating conditions for
realignment. Certain parts of the Dynatuner have been
preset close to the proper operating point. These include
the LF. transformers, the discriminator transformer, the
multiplex transformers, and the slug-tuned coils on the
PC-7 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 proceede
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 be allowed before realign-
ment following any tube replacement on PC-7 and PC-S.

On top of the tuning capacitor C1 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.

1( ) Turn in the screw C1»D 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 Vi turn counter
clockwise.

2( ) Turn in the screw Cl-B on the rear (R.F.) section
until it is in fully, but do not force it. Then back it
off In turn counter-clockwise.

3( ) The oscillator trimmer capacitor C8 screw (acces-
sible from below the chassis) should be turned until
the head of the screw is 5/16 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 tune
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 tool should be used to adjust