HP 212A - Page 22

When replacing V6 and Vlb, the replacement tube should be a
type WP45B.
The HP45 is specially manufactured for use in the
Model 21ZA.
If a standard 3C45 thyratron is used for replace-
ment, aging will be necessary (see following paragraphs).
It may
be expected that a high percentage of standard 3C45 replacements
will not successfully operate in this instrument, If a type HP45B
is used, aging and tube selection should not be required.
When a 3C45 is used to replace a thyratron in the Model 212A
Pulse Generator, proceed as follows:
1.
Remove screen cover from the back of the instrument.
2. Release tube clamp and remove suspected thyratron. Place
asbestos cover over replacement tube, place tube in socket
and tighten clamp.
On V6 also change plate shield to new
tube.
3. Prepare to operate instrument. Set the SYNC SELECTOR
switch to the - or +. position ea the instrument will not pulse
when turned on.
Set RATE control to minimum and the
PULSE LENGTH contra to 10 microseconds.
4.
Turn instrument on and allow to heat for approximately
ten minutes.
5, Set the SYNC SELECTOR switch to the Xl position. The re-
lay may chatter for up to one minute and stop.
6.
',Increase RATE control and decrease PULSE LENGTH con-
trol until a maximum rate and minimum pulse length are
obtained without relay chatter.
This process may take an
hour or more for some tubes.
7.
Allow instrument to run at maximum rate and minimum
length for approximately twenty -four hours.
Observe output
pulse,
If pulse is unsatisfactory due to excessive jitter or
slow rise or decay time, allow to run an additional twenty-
four hours. Again observe pulse. If, after seventy-two
hours of operation, the output pulse is still unsatisfactory
and the thyratron is known to be the cause of the trouble,
try another replacement thyratron.
5 REPLACEMENT OF LOAD RESISTOR R21 AND R22
The resistors used for R21 and R22 may be any of several differ-
ent types. A replacement resistor need not be identical, however,
it
must be non-inductive such as the deposited-carbon or metalized-
film types. The resistor must have not less than a 5 watt dissap-
ation rating.and should be within 5% of the value shown on the
schematic diagram.