Altec 436 a schematic

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Inc LANSING CURPURATIDN
YELEPHDNES CRestzw 551m BRADSHAW 77635.5

9356 SANTA MONICA BOULEVARD, BEVERLY HILLS, CALIFORNIA
AL-1277-1
TECHNICAL LETTER {fig /

b36A AMPLIFIER

The h36A Amplifier is described in the attached Operating Instructions. It is a
compressor of low cost and good quality. This amplifier is being used in a
number of unusual situations and some of these are outlined.

A local newspaper Want Ad Department receives want ads over the telephone from
varying local and suburban districts, and these are transcribed on a typewriter.
The volume has varied over a range of 20-30 db depending upon the loss of indi-
vidual circuits, and considerable parts of the message must be repeated because
of low intelligibility. When the h36A Compressor Amplifier was inserted in the
circuit, the volume from the distant originating area was raised so that it was
equal with the telephone call from a local area and satisfactory transcriptions
were made without repetition.

A local gas company recently instituted a program for teaching their employees

the proper conduct in discussing troubles with customers. An attempt was made

to tape record the telephone conversations and play them back to the employee,

but the volume varied over wide limits and unsatisfactory reproduction resulted.

The h36fi Compressor Amplifier was inserted between the telephone circuit and the .
tape recorder input and by means of the compressor action, the telephone conver- gfi
sation is of sufficient unifonnity in volume so that a good playback is obtained

for instructional purposes.

Recently one of the airlines in Los Angeles discovered that some of their
passenger agents were accepting gratuities so that a custmner could secure a
reservation on a plane and this had resulted in the plane being overbooked. A
supervisory circuit is being installed, using the h36A Compressor Amplifier, 50
that continuous monitoring of the incoming calls can be accomplished.

These examples indicate that there are many places in telephone company opera

tions with business concerns such as the airlines, Western Union, newspapers,
and department stores where this compressor anmlifier can be utilized to improve
services.

A freight trucking organization utilizes a telephone conference system to delay
discussing their many problems regarding re~routing of trucks and repairs on
equipment and other general business. These leased line facilities extend over
distances as great as 1,500 miles. There are several of their staff in each
city who participate in the discussion and a microphone and loudspeaker are
presently used on a press-to-talk basis. The h36A Compressor Amplifier enables
this conversation to be maintained at a uniform volume regardless of the cable'
losses.

AMPLIFIERS-TRANSFORMERS

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Rccently a drug company in Los Angeles installed a telephone conference hookup
so their main office executive organization could talk back and forth simul-
taneously to several distant city offices to save expense and travel time of
their executives to Los Angoles. The telephone company leased equipment for
this purpose as shown in schematic form in Figure 1. It is anticipated that
there will be a growing demand throughout the nation for this type of service
and Altec Lansing Corporation will provide the necessary'equipnent in complete
fonn, mounted and completely wired in a cabinet, so that it is only necessary
to make a connection to the phone line and the loudspeaker. In this applica-
tion, it proved desirable to increaSG the gain of the h36A, improve its input
balance, and raise its threshold to confine the range of compression to the
higher levels. The modification consists of replacing T1 with a TB-103 Input
Transfonner, removing R1, E2 and Cl, removing a connection between R10 and R11
junction and R7, installing 200K and 15K, 1/2 watt resistors and connecting
their junction with the junction of R10 and H11, and removing connection
between the primary of T1 and chassis ground. Drawing 6190 (attached) shows
the schematic after modification.

The h36A Compressor Amplifier has been used in conjunction with the 3i42A Ampli-
fier by making connections as described in Technical Letter #8.

Shielded wire of low capacity should be used between the amplifiers and should
be of minjmmn length. The build-out resistance 01 100K reduces the response of
the 3b2A L1 db at 50 cycles. This can be compensated for, if required, by
advancing the bass control from flat to a one o'clock position.

The procedure for proper operation is to open the input volume control to that
point where the desired amount or compression takes place. The master volume
control is then used to produce the required output power.

The 1136.. Amplifier is recommended for any public address system since it will
insure proper level with varying distance of the talker from the microphone, as
well as his relative loudness. ther unusual applications of this amplifier
will arise and we would appreciate being: infonned of them.

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