Sect. IV Page 4 Model 130B
push the chassis forward. At the primary of the ment, check the tubes. Adjustments made in an
power transformer (marked A), remove the wires attempt to compensate for a defective tube will
connecting terminals 2 and 5, and 1 and 4. Then often complicate the repair problem.
connect 1 to 2 as shown in Figure 4-2, and re-
place the 2 amp slow-blow fuse (F301)witha 1-1/4 It is a good practice to check tubes by substitution
amp slow-blow fuse. The instrument may now be rather than by using a ?tube checker?. The re-
connected to the 230 volt line. sults obtained from the ?tube checker? can be mis-
leading. Before removing a tube, mark it so that
if the tube is good it can be returned to the same
115 V CONNECTION 230V CONNECTION socket. Replace only tubes proved to be weak or
defective.
Any tube with corresponding standa.rd EIA (JEDEC)
characteristics can be used as a replacement.
Where variation in tube characteristics will affect
circuit performance, an adjustment is provided.
The following table lists the tests and adjustments
which should be performed if such tubes are re-
placed.
The chart in Table 4-2 lists all tubes in the 130B
Figure 4-2. Line Voltage Connection with their functions and adjustments required when
replacing tubes. The heaters of some tubes are
operated in series from a regulated dc voltage
obtained from the Low-Voltage Power Supply.
These tubes are identified in the chart with an
4-6 TUBE REPLACEMENT
asterisk and their heaters are shown in the Fila-
In many cases instrument malfunction can be cor- ment and Primary Detail Schematic. If a tube in
rected by replacing a weak or defective tube. Be- the dc string is pulled or burned out, all tubes in
fore changing the setting of any internal adjust- the string will be turned off. |