TM 9-4935-282-34
803D
(4) Allow to dry for 10 minutes. When it is cool or
recalibrated as in paragraph 4-4c.
humid, it may be necessary to place area under a lamp to
(2) Failure of the standard cell may occur if
ensure thorough drying.
subjected to below freezing temperature. The electrolyte will
(5) Coat any uncoated areas around R301 through
start to freeze at about 5 F and operation below 32 F is
R310 on the range resistor board and around the input to the
definitely not recommended. The life of the cell will also be
null detector chassis (tube V202, 5751, and chopper) with
greater if the 803D is not operated at elevated temperature.
Humi-Seal 1B12 (manufactured by Columbia Technical Corp.
The 8 to 15 year figure holds for operation of the instrument at
of Woodside, N.Y.).
normal room temperature, 72(+3)F.
e. STANDARD CELL PROBLEMS. The standard cell of
(3) The emf of the standard cell will change if the
the 803D and 803DR deserves special consideration if it is
cell has been inverted, or if the cell has been inadvertently
suspected of being faulty:
short-circuited. If the emf has changed, the 803D will naturally
(1) The standard cell used is a miniature
be out of calibration on all ranges. In either case, the cell will
unsaturated cell which has excellent long term stability and
return to its original emf. If the cell were inverted or shorted for
negligible temperature-voltage hysteresis.
(Temperature-
only a few seconds, the 803D should be able to measure
voltage hysteresis is the erratic behavior of the voltage while
voltages within specifications after several hours recovery time.
the cell is coming to equilibrium following a change in
f. DECIMAL LAMP REPLACEMENT.
The decimal
temperature.) Under normal conditions this cell should last
lamps are normal 6.3 volt lamps. To prolong their life these
from 8 to 15 years. In rare instances, failure has occurred in
lamps are operated from a 5 volt transformer winding.
less than 2 years. End of life is usually marked by an increase
However, these lamps do occasionally fail. To replace,
in temperature voltage hysteresis affect. That is, reading
proceed as follows:
errors in excess of 0.01% will result when the same voltage is
(1) On cabinet models , remove screws at back of
read with the 803D hot and cold. The emf of different cells
cabinet and slide instrument out of case. If only the upper
may vary as much as 0.05% and each instrument is calibrated
most decimal lamp needs to be replaced, proceed to step (6).
to its own particular standard cell. Thus, when the standard
(2) Remove four screws that hold front panel
cell is replaced, the 803D reference supply must be
assembly to chassis.
Symbol & Type
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
Pin 9
V101, 6BQ5
No
495
500
Heater voltage
No
680 to
No
680 to
Conn.
6.3 volts ac
Conn.
730
Conn.
730
V102, OG3
85
0
Int.
0
85
Int.
0
No
No
Conn.
Conn.
Pin
Pin
V104, 12AX7
217
84
36
Heater voltage
217
84
86
5.9 volts dc
See
Pin
V105, 12AX7
495
217
220
Heater voltage
500
217
220
4&5
6.3 volts ac
V202, 5751
60
-
0
Heater voltage
100
-
1.5
No
12 volts dc
Conn.
V203, 6AW8
47
45
140
Heater voltage
0.7
-
25
50
6.3 volts ac
V204, OA2
150
0
Int.
0
150
Int.
0
No
No
Conn.
Conn.
Pin
Pin
V501, 6EJ7
1.3
-
1.3
0
150
93
1.3
Heater voltage
5.9 volts dc
V502, 6AW8
28
-
200
1.8
-
100
150
(+50%)
This chart is to be used under the following conditions: (a) RANGE switch set to 500; (b) NULL switch set to VTVM: (c) all voltage
readout dials set to zero; (d) polarity switch set to +; (e) line voltage at 115/230 volts, 50 - 60 cycles; (f) all measurements made with
vtvm from negative binding post to specified terminal; and (g) all voltages may vary by 20% unless otherwise indicated.
Figure 4-2. TUBE VOLTAGE CHART
4-4
