HEWLETT PACKARD (HP) 212A
Manual de Servicio

The greatest duty cycle for the stop thyratron, V l b , occurs at m a x i m u m pulse rate and minimum pulse length. A t that time it is conducting for the longest period of time. Under these conditions the stop thyratren
w i l l be most subject to jitter and slowness.

ultivibrator tubes V l O l and V105 a r e particularly subject to microphonica. When changing V l O l and V105, it may be necessary to try several n e w tubes to obtain one which is not microphonic and which gives the required advance and delay. A small jump i the n trailing edge only would indicate that VlO8 is microphonic. .

-- Microphonic s usually appear as a small jump in pulse

A quick operational check for L2AU7 tubes can be made by exchanging with a 12AU7 not in a critical circuit, any position other than V l O l or

V105.
Interference Through Power Line Interference through the p o w e r line can occur when instruments on the line are not filtered or i f transformers connecting to the line do not have shields between the p r i m a r y and s e c ondary windings. The interference may appear i various forms. A n visual indication m a y be seen when viewing very low amplitude pulses on a very high sensitivity oscilloscope. The interference will cause ~ i n g i n g the leading and trailing edges of the pulse. at
Zn some models of the 212A Pulse Generator the filament transformer w a s constructed without an internal shield, Some of these models contained a line filter which is not shown in the schematic diagrams. If an instrument is known to cause interference through the power line, the line filter circuit s h o w n at the rear of the manual should be added.
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ADJUSTMENTS

Pulse Length Calibration The PULSE LENGTH dial is hand calibrate d to the potentiometer in the pulse length multivibrator circuit. Composition potentiometers vary greatly in taper and can change taper after use. The calibration of the P U L S E LENGTH dial will be onlyapproxim a t e l y correct a l t e r the potentiometer has been replaced or has aged. An external time standard is necessary where high accuracy is required.
Following replacement of a component within the circuits V108 the calibration of the P U Z S E LENGTH dial should be checked, I necesf sary, the dial calibration m a y be adjusted for greater accuracy as fallows:

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1.
2.

With pulse generator connected to a calibrated oscilloscope, s e t the PULSE LENGTH dial to 1Q.

If necessary, adjust C128 to obtain a pulse length of exactly 10
microseconds.