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Model 1415A Section IV
Paragraphs 4- 19 to 4-28
setting, this additional delay would place the leading and R423 to charge the input capacity ofV401. As the in-
edge too far to the right, and is therefore not used. put signal is gradually scanned, thevoltage on this ca-
pacity will vary accordingly and will be amplified by the
4-19. RAMP COMPARATOR. vertical amplifier for display on the CRT screen.
4-20. The ramp comparator compares the amplitudes 4-23. VERTICAL AMPLIFIER.
of the slow and fast ramps, and when they are the
4-24. The vertical amplifier, Figures 4-4 and 5-23,
same, produces a trigger pulse which operates the amplifies the input signal appearing at the grid of
sampler circuit. The slow ramp is applied through V401 in the sampler circuit. The first three stages
emitter follower Q301 to Q302, which is normally
conducting through CR301 and R302. When the fast comprise a differential feedback amplifier which
ramp, applied to the base of Q303, passes the has a gain inversely proportional to the value of
feedback resistance inserted by SENSITIVITY switch
instantaneous amplitude of the slow ramp, the com- S502. Zero Set adjustment R527 sets the voltage at
parator switches, with Q302 cut off and Q303 con- the grid of V503 to be zero with the VERTICAL
ducting. The resulting negative step at the collector
of Q303 causes tunnel diode CR303 to switch also, POSITION control centered, so that switching of the
and the sharp negative step at the base of Q304 Neg Up/Pos Up control will not cause a vertical
(+15 volts to +14. 5 volts) turns this transistor on. shift of the trace. The vertical signal may be inverted
by switching S501 to Neg Up, which reverses the dif-
The inverted (positive) step at the collector of ampli- ferential signal applied to the grids of V502A/B.
fier Q304 is differentiated by C306 and R305 to pro- Calibration of the vertical amplifier is accomplished
duce a positive spike which triggers sampler trigger
generator Q307/Q308. Negative spikes are removed by adjusting STEP CAL R574, which shunts part of
by CR304. The positive spike cuts off Q307, which the signal at the input of V502, and variable VERNIER
turns on Q308, and an output step rising from - 12. 6 control R575 which adjusts the degree of degeneration
in the output stage. Broad bandinterference is elimi-
volts to 0 is applied to Q401 in the sampler circuit. nated, or attenuated in the case of a high amplitude
This step is the trigger which initiates sampling, and interference, by adjusting R598A/B (BW) which re-
since the slow ramp applied to the comparator is
gradually rising in voltage, each output trigger to duces the bandwidth of the vertical amplifier, there-
the sampler will occur slightly later from the refer- by rejecting more of the interference band. Differ-
ential output signal is applied through pins 12 and 24
ence time (start of the first ramp). Thus, since the of P1 to the CRT vertical deflection plates in the
signal to be sampled occurs at a fixed, specific time oscilloscope. A single-ended output is taken from
after the reference time, scanning of the signal will the plate of V502A and passed through Q505 to be
begin before the step output appears, and will con-
tinue considerably after it appears (depending on made available at the front-panel RECORDER OUT
DISTANCE/ TIME settings). The steeper the slope of connector. The BEAM FINDER switch (located on
the oscilloscope front panel), when pressed, allows
the fast ramp (or the lower the slope of the slow ramp), R585 to be inserted in series with the V502 cathode
the faster will be the effective time scale; the deter- supply. This greatly reduces the tube current and
mining factor is how soon coincidence of the compara-
tor occurs after the reference time. stage gain, so that an off- screen beam will be brought
into view. Requiredadjustment of appropriate ampli-
4-21. SAMPLER. fier controls will then keep the trace on-screen when
the button is released.
4-22. The sampler circuit, Figures 4-4 and 5- 18, re-
ceives positive-going trigger steps from Q308 (nega- 4-25. HORIZONTAL AMPLIFIER.
tive steps from multivibrator Q307/Q308 have no effect 4-26. The horizontal amplifier, Figures 4-3 and 5-22,
on the following circuitry), eachwith gradually increas- receives the horizontal scan voltage, either the slow
ing separation from the reference time. The positive ramp or a manually determined voltage, amplifies
steps are differentiated by C401 and R402 into posi- this voltage, and applies it differentially to the hori-
tive spikes which trigger sampler pulse generator zontal deflectionplates of the CRT. DIST/TIME CAL
Q402, a blocking oscillator. The blocking oscillator adjustment R503 controls the degree of degeneration
waveform is converted by pulse transformer T401 in- in the amplifier, and HORIZ POS control R512 adjusts
to balanced voltage spikes: positive at terminal 4 of the DC level of the plates of V501A/B. The BEAM
the transformer, and negative at terminal 3. These FINDER operates in the Same way as in the vertical
spikes apply reverse bias to step-recovery diodes amplifier, described in Paragraph 4-24.
CR402 and CR403 which have an extremely sharp
recovery transition characteristic. Diode Biasadjust- 4-27. POWER SUPPLY.
ments R410 and R412 set the forward bias of CR402 4-28. Supply voltages of +250 volts, +lo0 volts, -100
and CR403 respectively for optimum pulse shape. volts, and -12. 6 volts are supplied by the oscillo-
The resultant sharp spikes (sampling pulses) are scope for operating most of the circuits in the Model
applied through C421 and C422 to forward-bias sam- 1415A. Two additional supply voltages are derived
pling diodes CR404 and CR405 respectively. Capa- from the +lo0 volts supply, as shownin Figure 5-24.
citors C421 and C422 almost immediately charge Two 15-volt avalanche diodes, CR601 and CR602 are
(or discharge) to the level of the input signal at that connected in series to provide a voltage of +30 volts,
instant, and after the very short samplingpulse ends, and an amplifier/emitter-follower circuit, Q60l and
the charge on these capacitors leaks through R422 Q602, provides an output of +15 volts.
01944-2 4- 5 |
ACEC
