RCA 77-DX User manual

4
BROADCAST AUDIO EQUIPMENT
Type 77-DX
Polydirectional Microphone
RADIO CORPORATIOn OF AMERICA
EnGInEERInG PRODUCTS DIVISIOn CAMDEn, n. J.
IB 24884 2

EQUIPMENT LOST OR DAMAGED IN TRANSIT
When delivering the equipment to you, the truck driver or carriers agent will pre,ent a receipt for your signature.
Do not sign it until you have (a) inspected the containers for visible signs of damage and (b) counted the containers and
compared with the amount shown on the shipping papers. If a shortage or if evidence of damage is noted, insist that
notation to that effect be made on the shipping papers before you sign them.
Further, after receiving the equipment, unpack it and inspect thoroughly for concealed damage. This should be done within
15 days, if possible. If concealed damage is discovered immediately notify the carrier, confirmed in writing and insist upon an
inspection and report.
In addition to the above, the shortages or damages should also be reported to RCA, but do not return any damaged equipment
unless we have furnished complete return shipping instructions.
Transportation companies are required to adjust for damage resulting from their negligence and RCA will assist you, if
necessary, in obtaining settlement. Accordingly, you should save all shipping papers, letters or invoices concerning the
shipment until it is certain that the equipment was delivered in good condition or until any damage has been adjusted.
REPLACEMENT PARTS
When ordering replacement parts, please give symbol, description, and stock number of each item ordered.
The part which will be supplied against an order for a replacement item may not be an exact duplicate of the original part.
However, it will be a satisfactory replacement differing only in minor mechanical or electrical characteristics. Such differences
will in no way impair the operation of the equipment.
The following tabulations list service parts and electron tube ordering instructions according to your geographical location.
SERVICE PARTS
LOCATION ORDER SERVICE PARTS FROM:
Continental United States, Alaska and Hawaii Service Parts Order Service, Bldg. 60, 19th & Federal Sts., Camden 5,
New Jersey or through your nearest RCA Regional Office. Emergency
orders may be telephoned, telegraphed, or teletyped to RCA Emergency
Service, Bldg. 60, Camden, N. J. (Telephone: WO 3-8000).
Dominion of Canada RCA Victor Company Limited, 1001 Lenoir Street, Montreal, Quebec
or through your local Sales Representative or his office.
Outside of Continental United States, Alaska,
Hawaii and the Dominion of Canada RCA International Division, Clark, N.J., U.S.A. or through your
local Sales Representative.
ELECTRON TUBES
LOCATION ORDER ELECTRON TUBES FROM:
Continental United States, Alaska and Hawaii Local Tube Distributor
Dominion of Canada RCA Victor Company Limited, 1001 Lenoir Street, Montreal, Que-
bec or through your local Sales Representative or his office.
Outside of Continental United States, Alaska,
Hawaii and the Dominion of Canada Local Tube Distributor or from:
Tube Department
RCA International Division
30 Rockefeller Plaza
New York 20, New York, U.S.A.
If or any reason, it is desired to return tubes, please return them to the place of purchase.
PLEASE DO NOT RETURN TUBES DIRECTLY TO RCA WITHOUT AUTHORIZATION AND SHIPPING
INSTRUCTIONS.
It is important that complete information regarding each tube (including type, serial number, hours of service and reason for its
return) be given.
When tubes are returned, they should be shipped to the address specified on the Return Authorization form. A copy of the
Return Authorization and also a Service Report for each tube should be packed with the tubes.
LIST OF RCA REGIONAL OFFICES
Boston 16, Mass. Chicago 5-i, Ill.
Room 2301, John Hancock Bldg. 1186 Merchandise Mart
200 Berkley St. Delaware 7-0700
Hubbard 2 -1700
Hollywood 28, Calif.
RCA Bldg., 1560 N. Vine St.
Hollywood 9-2154
Branch-San Francisco 2, Calif.
420 Taylor St.
Ordway 3-3027
Atlanta 3, Georgia
522 Forsyth Bldg.
Lamar 7703
Dallas 1, Texas
1907-11 McKinney Ave.
Riverside 1371
Plaza
Kansas City 6, Missouri
340 Dierks Bldg.
Harrison 6480
Cleveland 15, Ohio
1600 Keith Bldg.
Cherry 1 -3450
New York 20, New York
36 W. 49th St.
Judson 6-3800

BROADCAST AUDIO EQUIPMENT
INSTRUCTIONS FOR
Polydirectional Microphone
Type 77- DX
MI-4045-F and MI-11006-C
RADIO CORPORATION OF AMERICA
ENGINEERING PRODUCTS DEPARTMENT, CAMDEN, N. J.
P r i n t e d i n L. S. A.
5105-576

Figure I - Type 77 -DX Microphone
MI- 4045-F
Figure 2 - Type 77 -DX Microphone
MI- 11006-C

TECHNICAL DATA
Output Impedance
250 ohms may be changed to 30 or 150 ohms
Load Impedance
Unloaded input transformer
Effective Output Level
(all output connections)
Bi-directional (B) -50 dbm' GM -144db
Uni -directional (U) -53 dbm' GM -147db
Non-directional (N) -56 dbm' G M -150db
L -1, L-2, L -3, between -50 and -53 dbm
(GM = RETMA rating)
Hum Pick-up Level**
-128 dbm
Dimensions and Weight
Length - 11-1/2 inches
Width - 3 -3/4 inches
Depth - 2 -1/2 inches
weight - Total - 4 -1/2 pounds
Less cable - 3 pounds
Cable
MI -43 -c, 3 conductor, shielded,
30 feet long, no plug
Finish
TV Gray and Satin Chrome (MI- 4045 -F)
TV Gray (MI- 11006-C)
Stand Fitting
1/2 inch pipe thread
'Sound Pressure = 10 dynes /cm2
"Referred to a hum field of 1 x 10 -3 gauss.
DESCRIPTION
The RCA Type 77-DX Polydirectional Micro-
phones MI-4045 -F and MI- 11006 -C are high -
fidelity microphones of the ribbon type which
may easily be adjusted to obtain a variety of
directional patterns. Since the MI- 4045 -F
microphone is primarily intended for broad-
cast use, it is finished in satin chrome and
a low -gloss umber -gray enamel. The MI- 11006 -C
microphone is intended for television use and
is therefore completely finished in a low-
gloss umber -gray enamel which eliminates
glaring reflections usually seen on highly
polished microphones.
1
Instead of being open on both sides as in
the conventional velocity microphone, the
ribbon element in this microphone is coupled
to an acoustic labyrinth which forms the body
portion of the microphone. The tube connect-
ing the back of the ribbon to the labyrinth
is slotted directly behind the ribbon and
fitted with an adjustable shutter to secure
various areas of opening. When the opening is
completely closed, the microphone operates as
a non -directional pressure microphone; at the
wide -open position the microphone becomes bi-
directional. With the proper size opening the
pattern becomes a cardioid by virtue of
the phase shift which occurs. Openings
smaller or larger than this critical size
produce directional patterns with various
sized rear lobes.
Different amounts of low- frequency attenu-
ation are obtained by a reactor shunting the
output.
APPLICATION
The microphones are intended primarily for
indoor use and if used outdoors may require
some additional protection against the wind.
The choice of directional patterns makes
possible a considerable degree of control of
the ratio of direct sound to reverberant
sound as well as the possible reduction of
unwanted sound such as audience noise in a
studio. The wide angle of pick -up provided by
the cardioid pattern is useful in covering
large groups with a single microphone. For
"close- talking" applications the non -
directional characteristic is of considerable
value since the low- frequency response is not
accentuated as in the case of a velocity
microphone. Numerous other applications of
the various directional patterns as well as
the different response curves will no doubt
suggest themselves to the user.
OPERATION
Mounting
The microphone will mount on any stand
having a 1/2 -inch pipe thread. Other stands
will require a suitable adaptor. The micro-
phone is cushion -mounted, and a fork mounting
is provided so that the microphone may be
fitted to the desired position.

2
Connections
As shipped the microphone is connected for
an output impedance of 250 ohms. To connect
the microphone for an output impedance of 30
or 150 ohms, first lower the bottom cover by
removing the four machine screws around the
rim of the cover. Pull the cover down until
the transformer terminal board connections
are accessible. For the proper cable con-
nections, refer to figure 3.
Directional Characteristics
The adjustable shutter over the slot in
the tube leading to the acoustic labyrinth
may be rotated by means of a screwdriver ad-
justment extending through the rear screen
flush with a designation plate.
The plate is marked U, N and B, as symbols
for the uni -directional, non -directional and
bi-directional patterns. Three additional
markings L -1, L -2, and L -3 are used as
reference points for other directional
patterns which may be obtained. Refer to
figure 4 for the patterns associated with
each of the six symbols. Stops are provided
on the continuously-variable pattern selector
at the six marked positions, although the
shutter may be set at any intermediate
position.
Frequency Response
At the bottom of the lower shell is a
screwdriver -operated selector marked M (music)
V1 and V2 (voice). The voice positions
connect a reactor across the entire secondary
or part of the secondary of the output trans-
former, depending on the switch position (see
diagram, figure 3). Refer to figure 5 for the
frequency-response characteristics of each
setting. As can be seen from the curves, the
reactor attenuates the low- frequency response.
This is especially desirable when the micro-
phone is less than three feet from the source
of sound and the low-frequency response would
otherwise be exaggerated.
Phasing
The Type 77 -DX Microphone is phased so that
the red cable lead is electrically positive
when the sound pressure on the front of the
microphone is in the positive half of the
cycle.
When the outputs of two or more microphones
are connected into a mixing circuit, it is
necessary that the outputs of all such micro-
phones h'ave the same phase relation. Other-
wise, the output of one microphone will
oppose the output of another, resulting in a
reduction in output, and introducing varying
degrees of distortion.
To check the phasing of two or more micro-
phones, connect one microphone to the associ-
ated amplifier input and set the volume
control to obtain the desired output, while
talking into the microphone. Then, connect
the second microphone in parallel with the
first and, without changing the volume
control setting, hold both microphones close
together and talk into them. If the volume
decreases from the previous level, reverse
the connections of one of the microphone
cables at the microphone plug. Check each
additional microphone for phasing in this
manner, and, if necessary, reverse the cable
connections to correct the phasing to agree
with that of the microphone already connected.
When the sound source is directed toward
the back of the microphone, there will be a
large phase shift when changing the pattern
selector from bi- directional to non-direction-
al or the reverse. The safest way to avoid
undesirable directional effects resulting
from the above is to set microphones operating
close to one another on the same directional
response position, or at least avoid having
some on the non-directional pattern and the
others on the bi- directional pattern.
Directional Setting
The proper position of the pattern se-
lector depends upon the particular instal-
lation. The same holds true for the placement
of the microphone. Consult figure 4 for the
directional patterns of the six reference
positions.

3
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CABLE CONNECTIONS
M I- 4045 E aMe! M/-404SF
MI - I 1 706 B an! MI-//006C
M - 149778
Figure 3 - Schematic and Connection Diagram
Frequency Response Settings
For sound sources greater than three feet
from the microphone the frequency response
selector can be used in the M position for
any of the directional response patterns. If
the non -directional characteristic is used,
no low- frequency attenuation should be re-
quired even for very small distances. If
the bi- directional or uni- directional
patterns are used, low- frequency attenuation
will be required when the sound source is
less than 3 feet from the microphone, unless
special effects are desired. It is suggested
that the VI position be used for distances
down to 1 foot and the V2 position for still
shorter distances. Refer to figure 5 for
frequency-response curves of the M, V1, and
V2 settings.
Hum
Hum may originate in any part of the audio
system. In the microphone circuit, it may
result from ground loops or unbalance caused
by improper cable connections to the pre-
amplifier terminal board or microphone plug.
Hum may also be induced into the microphone
transformer or ribbon by magnetic fields
emanating from power transformers or electri-
cal machinery. In the Type 77 -D Microphone
the design of the ribbon circuit and the
transformer, and the thorough shielding of
the transformer have reduced hum pickup from
these sources to a minimum. In the event that
exceptionally strong fields are encountered,
the induced hum may be minimized 6,y turning
or tilting the microphone, or changing its
location. Turning the frequency response
selector to the VI or V2 positions will also
reduce the hum together with the overall low-
frequency response.
MAINTENANCE
It is recommended that no attempt be made
to make repairs other than replacement of
screens, transformers, mounting parts and
cables. For microphone mechanism repairs,
return the unit to the factory. Secure a
Repair Order and Returned Apparatus Tag from
the RCA Field Office or write to RCA Service
Company, Returned Apparatus Control, Carden,
N.J. Attach the tag, properly filled out, to
the damaged equipment and send the equipment
and the repair order to the manufacturer.
CAUTION: To prevent permanent damage
to the ribbon do not test continuity
of the microphone with a circuit
checker without connecting a resistor
of at least 5o,000 ohms. in series.

4
Figure 4 - Directional Patterns

5
+5
0
VlJ 5
WCO
W 10
0
15
20
+5
0
OPEN CIRCUIT RESPONSE
OF A TYPICAL
TYPE 77DX MICROPHONE
M
V2
UNIDIRECTIONAL POSITION
60 100 1000 10,000 15,000
15
+5
0
5
V2 BIDIRECTIONAL POSITION
60 100 1,000 10,000 15 000
V2
NONDIRECTIONAL POSITION
60 100 1,000
FREQUENCY IN CYCLES PER SECOND
10,000 15,000
472178-0
Figure 5 - Frequency Response Curves

6
SCREEN ASSEMBLY
50906
RIBBON CLAMP
*54127
RIBBON
1145385
RIBBON CLAMP
*54329
RIBBON CLAMP
*52920
THUMBNUT
95219
FORK
818393
REACTOR
097504
RIBBON CLAMP SCREW
*97472
SCREW
*54327
SCREW
54327
SCREW
*52469
SCREW
*97472
STOP
WASHER
*95220
BUSHING
095218
THRUST
Wf SH ER
*97502
ACOUSTIC LINE
ASSEMBLY
93981
TRANSFORMER
097503
SWITCH
THUMBNUT 1 ,I - 050915
50907
CUSHION
44677
CUSHION
MOUNTING
SSE M BLY
50925
. MN !Igibl
m..114144
STUD
93817
CAP NUT
*95216
PLATE
850909
INDICATOR
56702
SHUTTER
050910
GASKET
*44671
MOTOR AS EMILY
REAR VIEW
SPRING
NUT *44440
*50908
CABLE CLAMP
M 19828
CABLE
MI -43C
SPECIFY
LENGTH
STRAIN RELIEF
*58678 ,a45.2
Figure 6 - Parts Location Diagram of MI-4045 -F
with the checker. When testing the
microphone lines, observe the same
precautions or rake certain that the
microphones are disconnected.
To remove the top screen assembly for re-
placement, first remove the side thumbscrews
and mounting hardware at the top of the
microphone fork. Then, unscrew the two
machine screws on the side bands near the
top, and lift the screen assembly off the
microphone.
To remove a transformer, reactor or cable
for replacement purposes, first lower the
bottom cover as described under Connections.
Before removing the cable, be sure to loosen
the cord guard and cable clamp.
CAUTION: Xeep the microphone away
from iron filings or magnetic dust.
Although the screens provide ex-
cellent protection, minute iron
particles commonly found on work
benches and in maintenance shops
may be drawn through the screen by
the powerful magnet. If allowed to
accumulate, these particles may
mar the quality of reproduction.
REPLACEMENT PARTS
The following parts list is included to
provide identification when ordering replace-
ment parts. Order from RCA Replacement Parts
Department, Camden, New Jersey, giving the
Stock Number and Description of the parts
wanted. Replacement parts supplied may be
slightly different in form or size from the
original parts but will be completely inter-
changeable with them.

LIST OF PARTS
Description Stock
No.
MI- 4045-F
Acoustic, line assy. less band,
transformer 6 switch assy. 93981
3ushing, brass, microphone fork,
swivel 0.296" 1g. x 0.373 0.D.
x 0.261 I.D. with 9/16 dia.
x 0.030 thick shoulder
95218
Clamp, cable, incl. bushings,
hex nut, and screw 19828
Cushion mounting assy. complete 50925
Cushion, rubber 1" dia. x 9/16"
thick with 1 /4" dia. hole in
center
44677
Fork, microphone fork casting only,
with 1/8" pipe threaded hole in
base and 1, 3/8" hole in ends of
prongs
18393
Gasket, cable, rubber 7/16" 0.D.
x 9/32 I.D. x 7/32 thick 44671
Aut, thumb, 1" dia. x 3/16" thick
with 1/8" pipe threaded hole in
center fork base locking
50907
7
Description Stock
No.
Nut, cushion retaining knurled
cap nut, with k1 1/8-32 inside
thread
95216
Nut, knurled, cable guard spring
retaining, 5/8 0.D. x 7/16 lg.
with 9/16-18 thread
50908
Aut, thumb, knurled fork swivel 95219
3/4" 0.D. x 7/32 thick with
1/4 -28 tapped hole in center
Plate, designation for poly-
directional char., diamon205158
shape with 1 /4" dia. hole
in center 6 2 mtg. holes
.104" dia.
Screen Assy. comprising front 50906
6 rear screen 6 band
Screw, washer hd. Á2-56 x 3/16" lg.
for screen 6 cover 52469
Spring, cable guard 4444Ú
'Stud, cushion mtg. 2 -3/32" lg.
with 1/8 pipe thread one end, 93817
1/4 " -20 x 3/8 lg. thread other end
SCREEN ASSEMBLY
x'93818
RIBBON CLAMP
54127
RIBBON
85385
RIBBON CLAMP
*44446
RIBBON CLAMP
.54329
RIBBON CLAMP
+52920
THUMBNUT
*95224
FORK
.'93975
RE ACTOR
97504
SCREW
-97472
SCREW
54327
SCREW
,154327
SCREW
*P52469
SCREW
i97472
STOP
WASHER
0,95225
BUSHING
J5223
THRUST
WASHER
4r 97505
ACOUSTIC LINE
ASSE MOLT
*93981
TRANSFORMER
97503
TUMBNUT
-93974
CUSHION
X44677
CUSHION
MOUNTING
ASSEMBLY
."93973
SWITCH
*509,5
STUD
93817
CAP NUT
95221
GASKET
*314671
NUT
W'50908
CABLE CLAMP
m.95972
STRAIN
REL IEF
158BTN
MOTOR ASSEMBLY
REAR VIEW
SPRING
*44440
CABLE
MI -43C
SPECIFY
LENGTH
Figure 7 - Parts Location Diagram of MI- 11006 -C

8
LIST OF PARTS (Continued)
Description Stock
No.
MI-4045-F (Continued)
Strain relief, black neoprene 58878
2- 5/16" .1g. with 0.308 dia. hole
Switch, rotary, single circuit, 50915
3 Pos. screw driver slotted
shaft, music -voice
Reactor, iron core, impedance at 97504
50 CPS, 0.5 v, 91 ohms, +7%,
-5% D.C. res. 28 ohms, round can
Transformer, microphone, tapped for 97503
30, 150, 250 ohms, output
impedances turns ratio 1:23.5
±2% round can
Washer, aluminum alloy, fork swivel
thrust, 9/16" 0.D. x 0.260 I.D.
x 0.190 thick
97502
Washer, stop, microphone fork
swivel stop washer, 9/16" 0.0.
x .0598 thick, with 1/4" x
95220
11/64" elongated hole in center
MOTOR ASSEMBLY
Clamp, ribbon, top large 54127
Clamp, ribbon, bottom large 54329
Clamp, ribbon top small 44446
Clamp, ribbon bottom small 52920
Indicator, shutter position,
indicator and adjuster 56702
Plate, shutter pressure, .012 thick
phos. bronze 2 -1/16" lg. x 7/16"
wide
50909
Ribbon, microphone, corrigated
aluminum foil, 2" 1g. x .054 wide 45385
Screw, fil. hd. *1-72 x 5/16" lg.
large ribbon clamps 97472
Screw, fil. hd. *0-80 x 1/8" 1g.
small ribbon clamps 54327
Shutter, acoustic tube, .005 thick
phos. bronze, cam shaped 50910
MI- 11006 -C
Acoustic line assy. less band
transformer 6 switch 93981
Bushing, brass, microphone fork
swivel, 0.296 lg. x 0.373 0.D. x 95223
0.261 I.D. with 9/16" dia. x 0.030
thick shoulder
Clamp, cable clamp including
bushing & hardware 93972
Cushion, mtg. assy. complete 93973
Cushion, rubber, 1" dia. x 9/16
thick with 1/4" dia. hole in
center
44677
Fork, microphone fork casting only,
with 1/8" pipe threaded hole in
base and 1, 3/8" hole in ends of
prongs
93975
Gasket, cable, rubber, 7/16" 0.D.
x 9/32 I.D. x 7/32" thick 44671
Nut, cushion retaining knurled cap
nut, with *1-1/8-32 inside thread 95221
Description Stock
No.
Nut, thumb, 1" dia. x 3/16" thick,
with 1/8" pipe threaded hole in
center, fork base locking
93974
Nut, thumb, knurled fork swivel, 95224
3/4" 0.D. x 7/32" thick, with
*1 -4-28 tapped hole in center
Nut, knurled, cable guard spring
retaining, 5/8 0.D. x 7/16" lg.
with 9/16-18 thread
50908
Plate, designation, for poly-
directional char., diamond shape
with 1/4" dia. hole in center,
and 2 mtg. holes .104 dia.
205159
Reactor, iron core, impedance at 97504
50 CPS 0.5 v 91 ohms, +7%, -5%
D.C. res. 28 ohms round can
Screen assy. comprising front 6
rear screen and band 93818
Screw, for screen 6 cover 52469
2 -56 x 3/16" lg.
Spring, cable guard 44440
Stud, cushion mtg. 2 -3/32" lg. with 93817
1/8 pipe thread one end, 1/4-20 x
3/8 lg. thread other end
Strain relief, neoprene black, 58878
2 -5/16" lg. with 0.308 dia. hole
Switch, rotary, single circuit, 50915
3 pos. screw driver slotted shaft,
music -voice
Washer, aluminum alloy, fork swivel
thrust, 9/16" 0.D. x 0.260 I.D., 97505
0.190 thick
Washer, stop, microphone fork
swivel stop washer, 9/16" 0.D. x 95225
.0598 thick with 1/4 x 11/64"
elongated hole in center
Transformer, microphone, tapped
for 30, 150, 250 ohms output
impedance turns ratio; 23:5
97503
±2%, round can
MOTOR ASSEMBLY
Clamp, ribbon, top large 54127
Clamp, ribbon, bottom large 54329
Clamp, ribbon, top small 44446
Clamp, ribbon, bottom small 52920
Indicator, shutter position,
indicator and adjuster 56702
Plate, shutter pressure, .012 thick
phos. bronze 2-1/16" lg. x 7/16"
wide
50909
Ribbon, microphone, corrigated
aluminum foil, 2" lg. x 0.054 wide 45385
Screw, fil. hd. *1-72 x 5/16 1g.
for large ribbon clamps 97472
Screw, fil. hd. N0 -80 x 1/8" lg.
small ribbon clamps 54327
Shutter, acoustic tube, .005 thick
phos. bronze, cam shaped 50910

MIME
MEE
MIRINIIII
IEEE
INNS
MIMI
RADIO CORPORATIOCI OF AMERICA
EnGInEERIfG PRODUCTS DIVISIOn CAmDEn, n. J.