Model 122A Sect. I Page 1
SECTION 1
GENERAL INFORMATION
1-1 GENERAL DESCRIPTION 1-3 POWER LINE VOLTAGES
The Model 122A is a dc to 200 kc dual-trace This instrument is designed to operate from a nom-
cathode-ray oscilloscope. It has accurately cali- inal 115 or 230 volt source. The instrument will
brated input sensitivity and sweep-speed ranges. operate satisfactorily over a *lo% variation from
This oscilloscope features dc-coupled differential the nominal value, i.e. 103-127 volts. Operationat
amplifiers and dual-trace operation. 130/260 volts will damage the instrument. If ab-
normally high line voltage is suspected monitor the
line voltage to be certain it does not exceed
Differential amplifiers are useful since they reject
127 volts.
the common-mode (in-phase) part of the input while
amplifying the differential (out-of-phase) part. For
instance, they will reject hum pick-up while am-
plifying the desired signal. In addition, using dif- 1-4 CONVERSION FOR 230 VOLT OPERATION
ferential amplifiers has other advantages. Nor-
The instrument can be converted from 115 v to
mally dc amplifiers are difficult to keep stable.
230 v operation by reconnecting the power trans-
Changes such as aging and changes of potentials
former dual primary windings as follows: Remove
cause this drift. However, these changes are of
the instrument from the cabinet by removing the
the common-mode type and are rejected by dif-
two large screws from the rear of the cabinet. Push
ferential amplifiers. Thus differential amplifiers
the instrument from the cabinet by pushing on the
are also used to stabilize dc amplifiers.
rear of the chassis.
Dual-trace operation is obtained with an electronic Locate the power supply terminal strip situated
switch. This permits observation of two signals next to the power transformer. The twoouter ter-
at the same time. The two signals may be viewed minals on each side are jumpered together connect-
either alternately during consecutive sweeps or ing the windings in parallel. Remove these jumpers.
chopped on each sweep. Chopped operation involves Connect an insulated jumper between the second
switching rapidly between the two signals so that and fourth terminals, connecting the windings in
both appear to be traced simultaneously. The most series. Refer to the Low Voltage Power Supply
useful type of presentation in each case will depend Schematic for details. Replace the 2.0 amp slow-
upon the frequencies involved. Generally, chopped blow fuse with a 1.0 amp slow-blow fuse.
operation is used with low frequency signals. These
signals may also be viewed separately or with their
difference (B-A) displayed on the screen.
1-5 ACCESSORIES AVAILABLE
An AC-83 Viewing Hood is available at extra cost.
This is a face-fitting moulded rubber hood used to
1-2 DAMAGE IN TRANSIT
shade the face of the cathode-ray tube under high
Refer to the warranty page in this manual if any ambient light conditions. It will permit the useof
damage is apparent upon receipt. lower beam intensity setting. |