Tape Recording Magazine - AmericanRadioHistory.Com

In this well in the side of the case can be
found the power and audio inputs as well as
a 110 volt output receptacle.
turntable, a pre -amplified microphone,
AM -FM tuner, etc. in addition to the
tape recorder.
HUM -( Continued from page 45)
impedance microphone type not in excess
of 25 feet in length. The transformer
is an interstage audio type available
at any amateur radio supply store.
If possible, stick closely to the values
shown or you may get distortion. UTC
or other medium quality interstage
transformers "plate to single grid" 10,-
000 to 50,000 ohm or "push-pull plate
to grid" of low ratio ( omit the center
tap) will be satisfactory. Connect the
high impedance side to the audio
device.
The method shown in Figure 3 may
provide an acceptable recording but its
shortcomings lie in high hum level except
in exceptional audio systems. Extraneous
noise and room noise pickups,
caused by the loudspeaker acting as a
microphone and impedance variations
due to speaker load changes at various
frequencies may give trouble. This
method is at best an expedient. R -1
should be a one watt carbon resistor,
R -2 a 2 watt carbon and the cable
should be (high impedance) shielded
microphone type, not in excess of 25
feet. The transformer is a UTC or
other medium quality "plate to voice
coil" 10,000 to 4 ohm. It is inverted in
connecting and bridged across the voice
coil of the loudspeaker using the impedance
matching "pad" as shown.
Pickups made by placing the microphone
in front of the loudspeaker may
provide experience in microphone use
but in general will result in poor recordings.
If a mike pickup is your only
choice, wrap the mike loosely in gauze
or a handkerchief, place it close to the
speaker and hope for the best.
Where long runs between units (in
excess of 25 feet) must be used, im-
Also provided is a power output receptacle
in the well on the side of the
case and an extension speaker jack on
the face of the panel.
The speaker jack can be used to feed
a major speaker enclosure or PA system
and when in use the speaker in the
case is cur off. This feature enables
the amplifier alone to be used.
The 620 was a stock model in its
original carton. The workmanship of
the unit showed care. It was well assembled
and had a fine, quality appearance.
We feel that this unit is worth the
price asked and that we can recommend
it without hesitation for its fine performance.
As noted above, it exceeded
the claims made for it by Ampex.
pedance conversion is required. See
Figure 4. A choice of two low itripedances
is available and the quality of
either method is excellent. One or the
other may be used, depending upon
your choice of material; however, once
you settle on one method don't try to
mix components.
Figure 4A indicates connections and
materials for a 30/50 ohm connecting
system and the two transformers are
used "back to back" using conventional
hi -lo units made by Shure, Electro-
Voice, UTC and many others. The
transformer ratio is nominally 15,000
to 30/50 ohm ratio. The cable is 30/50
ohm single conductor shielded microphone
cable of the "Belden" type. Runs
in excess of 250 feet require equalization
to compensate for the attenuation
of the high frequencies.
Figure 4B is for 500/600 ohm conversion
and the transformers may be
any good "plate to line" UTC, Chicago
or other make, connected "back to
back" at each end of the shielded two -
conductor (600 ohm nominal) inside
wire. This is commercially coded SH 22
or 19 gauge inside wire. Lengths up to
500 feet may be used without the need
of equalization.
Competent and balanced equalization
is much too complicated a subject to
take up here but in general the bass
and treble boost of your amplifier will
more than compensate for moderately
longer extensions of Figure 4B.
The hookups shown are for average
recorders and will produce good to excellent
results. If you desire perfection
then you will have to buy professional
radio -station type equipment which
runs into hundreds and sometimes thousands
of dollars.
TERADO - for
Tape Recording
Jrtywliere
the
'CHIEF"
Auto -
matic
On -Off
Switch
Trav- Electric
CONVERTERS
Provide House Current in
Truck, Boat, Plane.
Hail to the "CHIEF"
6 -81160 - FOR 6 VOLT BATTERIES
OUTPUT 75 TO 100 WATTS - LIST $49.95
12 -81160 - FOR 12 VOLT BATTERIES
OUTPUT 100 TO 125 WATTS - LIST $54.95
Indispensable
in Mobile Units
The "CHIEF" operates:
-TAPE RECORDERS
-WIRE RECORDERS
-AMPLIFIERS
-PUBLIC ADDRESS SYSTEMS
ELECTRIC DRILLS
DICTATING
MACHINES
LIGHTS
and also
HAND
VACUUM
CLEANERS
BUSINESS
MACHINES
-other Tray-Electric Models
from 10 to 75 Watts
List -511.95 to $37.95
operate Electric Shavers, lights, Phonographs,
Test Equipment, Heating Pods, Small Soldering
Irons, Short, Long Wave Radios, Turn -
lobles.
See your Electronic, Automotive,
or Hardware Jobber or Dealer, or
Write Direct
TERADO COMPANY
Mfrs. of Electronic Equipment
1054 Raymond Ave., St. Paul 14, Minn.
In Canada Write: Atlas Rodio Corp., Ltd.
560 King St. West, Toronto 2E, Ont.
Export Soles Division:
Scheel International, Inc.
4237 N. Lincoln Ave., Chicago 18, 'II., U.S.A.
Cable Address- Harsheet
49