Sect. IV Page 5
5) Measure the voltage between pin 5 of tube V6 Control R49 varies the level to which the output of
and B-. This voltage should be about + 7 5 volts. the integrator rises in a positive direction and A51
Variations in OA3 tubes can cause this voltage to varies the level of the negative excursion. b6s The
fall at any point between 68 and 85 volts. levels of the shaper diodes are not variable and
therefore, the triangle input to the shaper can have
6) Repeat step 3 if you replace either V5 or V6. one and only one correct magnitude and average
The characteristics of cold-cathode regulator tubes level.
drift during about the first 72 hours of operation.
This drift can affect the 202A output. 72 A hour Figure 4-2 shows the situation at the shaper when
aging is recommended for a new tube for either the two reference levels are properly adjusted.
V5 or V6. Figure 4-2B shows the effect of having the reference
levels adjusted for too large a magnitude, but with
7) Test the regulated output voltage at pin 5 of tube the proper average value. Figure 4-2C shows the
V5 while varying line voltage between 103 and 127 effect of having reference levels adjusted for a
volts. The regulated voltage will normally not change triangle of the proper magnitude, but incorrect
by more than *l%. Check power supply tubes and average level. This indicates a close relationship
components if the change is excessive. between correct frequency calibration and minimum
distortion. In fact, the two conditions are simul-
taneously satisfied by optimum settings of the same
4-10 THEORY OF DC BALANCE AND adjustments.
DISTORTION ADJUSTMENTS
The output AMPLITUDE control is located at the
input to the output amplifier. If the dc component
4-11 DC BALANCE AND DISTORTION
at the output terminals is to be zero for all settings ADJUSTMENTS
of the AMPLITUDE control dc the levels at the ends
of the AMPLITUDE control must be the same and The following test procedure re@ires a dc voltmeter
also equal to the average level of the input wave. with an input resistance of at least 100 megohms
From the schematic wiring diagram, it is seen that such as an @Model 410B. In addition, the volt -
the common connection between the two sections of meter must not be grounded as the common side of
the control is connected to the cathode of V4. The the meter must be connected points to within the
level of this point can be adjusted to the desired value 202A that are not at ground potential. Distortion A
by R54. The signal impedance of this point is very Analyzer and an Oscilloscope will also be required.
low compared with the magnitude of the AMPLITUDE
control impedance, and therefore, the cathode of A 20 minute warm-up is recommended before you
V4 has virtually zero signal. start this procedure. You should also adjust the
power supply as outlined in paragraph 4-9.
When R49, R51, R54, and R60 are adjusted properly,
there is no dc component across either section of 1) Adjust the insulated 410B voltmeter to indicate
the AMPLITUDE control. 0.5 on the 1 volt range with the dc leads shorted.
Use either the "+" or the "-" position of the SEL-
When the FUNCTION switch is in the squarewave ECTOR switch -- whichever one will permit the
position, there is no signal input to one section of 0. 5 setting with the ZERO ADJ. control. This meter
the AMPLITUDE control, hence, the tap on that indication will be called "0 volts1' in the remaining
section merely carries the constant bias level set portion of this procedure.
by the cathode of V4. The other section is connected
through a network the to clamp section of the bi- 2) Connect the COMMON lead from the voltmeter
stable circuit. R22 d this network adjusts the aver- to the common junction of AMPLITUDE controls
age level of the squarewave applied to the amplitude R93A and R93B (violet wire).
control to the same value as the cathode of V4.
3) Connect the DC volts probe to the opposite end
The dc levels at the input to the amplifier are inde- of R93A. This is a slate wire connected to the AM-
pendent of AMPLITUDE control setting. dc The PLITUDE control.
levels of the two output terminals may be adjusted
to be equal by R65. Control R65 varies the dc level 4) Set the FUNCTION switch to TRIANGULAR and
of the signal on one grid of the second stage of the adjust R54 for a voltmeter indication of "0 volts".
amplifier. When these adjustments are made, the
dc component between the output terminals will 5) Move the DC volts probe to the arm of Rl18 and
remain at a very low value, independent of amplitude adjust R118 for an indication of approximately "0
setting or waveform selected. volts". |
ACEC
HEWLETT-PACKARD
