TM 11-6625-1559-12
Item
Trouble symptom
No.
Checks and corrective measures
Probable trouble
Check tube V401; replace as neces-
N o 1-MHa markers appear
6----
assembly.
Check tubes V401 and V402; replace
7---- No 10MHz markers appear
Check tube V402 or V403; replace
8---- No 100-MHz markers
Defective 10-MHZ or 100-MHZ
a s necessary (pars 4-15).
appear on oscilloscope
pattern.
fect is obvious or if the tube tester shows it to
4-15. Tube-Testing
Techniques
be defective. Do not discard a tube that tests
When trouble occurs, check all wiring and con-
at or near its minimum test limit on the tube
nections before removing any tubes. Try to iso-
tester. Put back the original tube, or insert a
late the trouble to a component or stage. If
new one if required, before testing the next one.
tube failure is suspected, use the applicable pro-
cedure described below to check the tubes.
Caution: Do not rock or rotate a tube when
a. Turn the fuseholder cap counterclockwise
removing it from a socket; pull it straight out
and remove it from the fuseholder.
with a tube puller.
b. Remove the defective fuse from the fuse-
a. Tube Substitution Method. Replace a sus-
holder cap.
pected tube with a new one. If the equipment
still does not work, remove the new tube and
put back the original tube. Repeat this procedure
Note. Be sure the B+ and B- fuses (F2 and F3) are
with each suspected tube until the defective tube
slow-blow types with a rating of 0.1 ampere.
is located.
b. Use of Tube Tester. Remove and test one
tube at a time. Discard a tube only if its de-
holder and turn it clockwise to tighten.