{"id":14291,"date":"2019-11-02T14:14:05","date_gmt":"2019-11-02T13:14:05","guid":{"rendered":"https:\/\/www.istitutomontani.edu.it\/museovirtuale\/?p=14291"},"modified":"2024-01-09T19:53:01","modified_gmt":"2024-01-09T18:53:01","slug":"oscilloscope-tektronix-type-565-serial-689-eighth-part","status":"publish","type":"post","link":"https:\/\/www.istitutomontani.edu.it\/museovirtuale\/oscilloscope-tektronix-type-565-serial-689-eighth-part\/","title":{"rendered":"Oscilloscope Tektronix Type 565 serial 689, sixth part (MITI Museum)"},"content":{"rendered":"

Oscilloscopio Tektronix Type 565. Sesta parte. <\/span>
\nNell\u2019inventario D del 1956 si trova al n\u00b0 3747 e risulta acquistato nell\u2019agosto del 1964; vi si legge: \u201cSilvestar ltd. Milano. Oscilloscopio Tektronix mod. 565 matr 689. Dest. Elettronica \u20a4 1^{\u0387<\/sup>678^{\u0387<\/sup>600\u201d. Insieme alla fotocamera che \u00e8 al n\u00b0 3746, dove si legge: \u201cSilvestar ltd. Milano. Macchina fotografica Tektronix mod. C-12 completa di Bezel-Tektronix. Dest. Elettronica. \u20a4 557^{\u0387<\/sup>700\u201d.
\n<\/span>Il testo continua dalla quinta parte.
\n<\/span>\u00a7\u00a7\u00a7<\/span><\/p>\n}}}

\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00abSECTION 3
\n<\/strong>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0CIRCUIT DESCRIPTION
\n<\/strong><\/span>General
\n<\/strong><\/span>This portion of the Instruction Manual presents a detailed
\n<\/span>discussion of the Type 565 circuitry operation. This discussion <\/span>refers to various block diagrams inserted in the text, and <\/span>to the circuit diagrams in the back of this manual.
\n<\/span>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0BLOCK DIAGRAM
\n<\/strong>A functional block diagram at the Type 565 Oscilloscope <\/span>is shown in Fig. 3-1. The relationship of the circuits in each
\n<\/span>block to those in other portions of the instrument is discussed<\/span>in the detailed description of that circuit.
\n $\"\"$
\n<\/span>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 TIME BASE TRIGGER
\n<\/strong><\/span>General
\n<\/strong><\/span>Time Base \u2018A\u2019 Trigger and Time Base \u2018B\u2019 Trigger circuits <\/span>are identical except for component reference numbers on
\n<\/span>the schematics. The following circuit description pertains
\n<\/span>to both circuits, but reference numbers for Time Base \u2018A\u2019
\n<\/span>Trigger are used.
\n<\/span>For best triggering stability, the Time Base Generator
\n<\/span>requires a trigger pulse that is representative of the selected
\n<\/span>triggering signal frequency, but otherwise consistent in
\n<\/span>amplitude and wave-shape. Available triggering signals often <\/span>vary in amplitude, waveshape, and frequency, and thus cannot <\/span>be used directly to trigger the time base. The Trigger <\/span>circuit is essentially a waveshaping circuit that converts a <\/span>sample of the input signal into a pulse having a reasonably <\/span>constant risetime and amplitude. Hence, frequency is the only <\/span>variable characteristic remaining in the output trigger pulse.
\n<\/span>The block diagram, Fig. 3-2, shows the two basic elements
\n<\/span>of the trigger circuit. The Trigger Input Amplifier amplifies
\n<\/span>(and when desired, inverts) the incoming triggering signal and <\/span>applies it to the input grid of the Trigger Multivibrator. The <\/span>Trigger Multivibrator is essentially a switch that is either <\/span>on or off, depending on the instantaneous voltage level at its <\/span>input.\u00a0 Its square wave output is applied to the Time Base <\/span>Generator where it is differentiated to form positive and <\/span>negative pulses. The negative pulses trigger the Time Base <\/span>Generator while the positive pulses are clipped and not <\/span>used.
\n $\"\"$ <\/span>For the following description, refer to the Time Base \u2018A\u2019
\n<\/span>Trigger schematic in the back of this manual.
\n<\/span>Trigger Input Amplifier
\n<\/strong>The TRIGGER source switches are used to select the
\n<\/span>appropriate trigger signal from one of four sources: upper beam <\/span>vertical plug-in unit (UPPER BEAM), lower beam vertical <\/span>plug-in unit (LOWER BEAM), TRIG. IN connector (EXT.), or <\/span>line-frequency signal from the power transformer (LINE). The<\/span>selected signal is then applied to the COUPLING switch. <\/span>(Information about the automatic mode, AUTO., of trigger <\/span>operation is given later in this circuit description).
\n<\/span>The COUPLING switch permits the operator to accept or
\n<\/span>reject certain characteristics of the triggering signal. In <\/span>the DC position, the coupling capacitors are shorted, coupling
\n<\/span>both dc and ac signals to the Trigger Input Amplifier. In
\n<\/span>the AC position, C7 and C8 in parallel are placed in the
\n<\/span>signal path. An RC circuit consisting of C7-C8 and R12 is thus <\/span>formed which blocks dc and attenuates ac signals below <\/span>about 20 cycles. In the AC FAST position, C8 alone is placed <\/span>in the signal path and R12 is placed in parallel with R10. This <\/span>RC network blocks dc and rejects ac signals below 1000 <\/span>cycles. The TRIGGER source and COUPLING switches are <\/span>wired so the AC FAST function is bypassed when the LINE <\/span>source is used.
\n<\/span>The signal from the COUPLING switch is applied to the
\n<\/span>SLOPE switch through R15-C15. (R15 and C15 prevent high <\/span>amplitude positive signals from drawing excessive grid
\n<\/span>current from V24.) The SLOPE switch determines whether or <\/span>not the triggering signal will be inverted by the Trigger Input <\/span>Amplifier. When the SLOPE switch is set to \u2014, the signal <\/span>is applied to the grid of\u00a0 V24A and will not be inverted. For <\/span>example, a positive-going signal at the grid of V24A will <\/span>cause a positive-going change in the common cathode <\/span>circuit. The fixed voltage at the grid of\u00a0 V24B and the <\/span>positive going change at its cathode reduce the current through <\/span>V24B. This results in a positive-going change in plate voltage; <\/span>hence, no inversion.
\n<\/span>If the SLOPE switch is in the + position, the signal is <\/span>applied to the grid of\u00a0 V24B. In this case, V24B inverts the
\n<\/span>signal in the manner characteristic of a single stage, <\/span>plate-loaded amplifier.
\n<\/span>The SLOPE switch also serves another function, it applies
\n<\/span>a dc voltage from the LEVEL control to whichever grid of V24 <\/span>is not connected to the COUPLING switch. (The need for this <\/span>dc voltage is explained in the Trigger Multivibrator portion <\/span>of this circuit description. At this point, however, the <\/span>important consideration is the effect the dc voltage has on <\/span>the amplified trigger signal at the plate of\u00a0 V24B.)*
\n<\/span>The voltage at the junction of R19 and R20 can be varied
\n<\/span>between about +15 and -15 volts by adjusting the LEVEL
\n<\/span>control. This voltage controls the average voltage at the <\/span>plate of\u00a0 V24B and the triggering signal either adds to or
\n<\/span>subtracts from that average. Thus, in addition to being an
\n<\/span>amplifier, the Trigger Input Amplifier is also a voltage
\n<\/span>comparator. (V24 is a voltage comparator rather than a
\n<\/span>difference amplifier since R24 and C24 balances the gain of V24A <\/span>to that of V24B.)\u00a0 This composite signal is applied to the <\/span>input grid of the Trigger Multivibrator.
\n<\/span>The Trigger Multivibrator is disabled unless R47 is grounded.
\n<\/span>If the UPPER HORIZ. DISPLAY switch, LOWER HORIZ.
\n<\/span>DISPLAY switch, or \u2018B\u2019 MODE switch is set for a function <\/span>in which the operation of Time Base \u2018A\u2019 is required, then
\n<\/span>R47 will be grounded.
\n<\/span>Trigger Multivibrator
\n<\/strong><\/span>The Trigger Multivibrator, V45, is a typical bistable Schmitt
\n<\/span>circuit. When the voltage at the grid of V45A is above a
\n<\/span>certain level, V45A conducts and V45B is cut off. In this state, <\/span>the output voltage at the plate of\u00a0 V45B is +300 volts. When <\/span>the voltage at the grid of\u00a0 V45A is below a certain level, V45B <\/span>conducts and V45A is cutoff. The output voltage at the plate <\/span>of\u00a0 V45B is then about +293 volts. The transition from one <\/span>state to the other occurs very rapidly, regardless of how <\/span>slowly the input voltage passes the trip-level. Thus, the <\/span>output of the Trigger Multivibrator is a square pulse of about <\/span>7 volts amplitude. The following example illustrates the <\/span>sequence of events.
\n<\/span>When a negative-going voltage change reaches about <\/span>+111 volts at the input grid, the plate of\u00a0 V45A rises and <\/span>carries the grid of\u00a0 V45B with it. V45B is driven into conduction <\/span>(see Fig. 3-3). Since the cathode resistor R47 is common <\/span>to both tubes, the conduction of\u00a0 V45B tends to raise the
\n<\/span>cathode voltage of\u00a0 V45A. This further reduces the current
\n<\/span>flow through V45A and compounds the original action of the <\/span>input signal. V45A and V45B rapidly change conduction <\/span>states; V45A cuts off and V45B conducts. The voltage at the <\/span>plate of\u00a0 V45B drops sharply. This voltage step is applied to <\/span>a differentiating network in the Time Base Generator and <\/span>becomes the negative-going trigger pulse required to start the <\/span>time base action.
\n $\"\"$
\n<\/span>As the input signal continues into the positive-going <\/span>portion of a cycle, the grid of\u00a0 V45A rises beyond +111 volts <\/span>to about +113 volts before the Trigger Multivibrator resets <\/span>to its previous state. This approximate 2 volt difference in <\/span>switching levels is the hysteresis range of the circuit.
\n<\/span>As Fig. 3-3 and the previous description suggest, there <\/span>are two basic requirements that must be met if the Trigger <\/span>Multivibrator is to generate an output pulse. First, the
\n<\/span>amplified signal at the grid of\u00a0 V45A must have enough
\n<\/span>amplitude to overcome the hysteresis of the circuit; that is, about <\/span>2 volts peak to peak, or more. Second, the signal must <\/span>be superimposed on a dc voltage that will permit it to <\/span>cross the upper and lower hysteresis limits of the circuit; <\/span>that is, about +111 volts and +113 volts. This second <\/span>requirement is met through the use of the LEVEL control <\/span>mentioned previously. Figures 3-4 and 3-5 illustrate the consequence <\/span>of improper LEVEL control adjustment. In both <\/span>cases, the signal amplitude is adequate to produce triggering, <\/span>but the dc level of the signal is incorrect.
\n<\/span>Automatic Triggering<\/strong>\u2014Automatic triggering may be
\n<\/span>selected by placing the LEVEL control in the AUTO. position.
\n<\/span>This changes circuit operation as follows:
\n<\/span>A section of the AUTO. switch in the input coupling <\/span>circuit selects AC coupling, regardless of the position of the <\/span>COUPLING switch, so the average voltage of the triggering <\/span>signal is reduced to zero. The junction of\u00a0 R19 and R20 is
\n<\/span>grounded so the amplifier will be balanced. <\/span>C31 is inserted between V24B and V45A and the Trigger <\/span>Multivibrator is converted into an astable or free-running <\/span>form by providing positive feedback to the input grid. In <\/span>the absence of an input signal, the multivibrator free-runs <\/span>at about 50 cps; a frequency determined primarily by C31 <\/span>and R40. An incoming signal having a frequency greater than <\/span>about 50 cps will force the multivibrator to run at the signal
\n<\/span>frequency.
\n<\/span>Resistance added in the plate circuit of\u00a0 V45A increases <\/span>the circuit gain and reduces the hysteresis to considerably <\/span>less than 2 volts. This permits low amplitude signals to <\/span>produce stable automatic triggering.
\n $\"\"$ $\"\"$
\n<\/span>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 TIME BASE GENERATORS
\n<\/strong>The following description pertains to both time bases, <\/span>but circuit reference numbers for Time Base \u2018A\u2019 are <\/span>used.
\n<\/span>The additional circuitry in Time Base \u2018B\u2019 is described in
\n<\/span> a later portion of this section under the title \u201cTime Base
\n<\/span>\u2018B\u2019 Lockout\u201d.
\n $\"\"$
\n<\/span>The Time Base Generator produces four output signals (see
\n<\/span>Fig. 3-6):
\n<\/span>1. a positive-going sawtooth which can be coupled to either <\/span>or both horizontal amplifiers by the appropriate setting <\/span>of the Horizontal Display switches. The sawtooth output <\/span>is also permanently connected to the Delay Pickoff circuit <\/span>(Time-Base \u2018A\u2019 only)
\n<\/span>2. a positive-going unblanking pulse having the same duration <\/span>as the sawtooth rise. Coupled to the Crt Circuit by
\n<\/span>the Horizontal Display switches to unblank the beam(s)
\n<\/span>being deflected by Time Base \u2018A\u2019.
\n<\/span>3. a positive-going pulse (+ GATE OUT) having the same <\/span>duration as the sawtooth rise. Coupled to a rear panel <\/span>connector for external use.
\n<\/span>4. a negative-going multi-trace sync pulse having the same
\n<\/span>duration as the sawtooth rise. Coupled to the appropriate <\/span>Vertical Plug-In Unit(s) by the Horizontal Display
\n<\/span>switches. The trailing edge of the pulse causes multi-trace
\n<\/span>plug-in units, operating in the alternate mode, to <\/span>switch channels.
\n<\/span>In most applications, each cycle of events is started by <\/span>a trigger pulse from the Time Base Trigger circuit. However <\/span>it is also possible to either disable the generator or to make <\/span>it free run; that is\u2014the end of one cycle will cause the next <\/span>cycle to begin. The desired mode of operation will be
\n<\/span>obtained through the appropriate setting of the STABILITY
\n<\/span>and LEVEL (FREE RUN position) controls. (See Section 2.)
\n<\/span>The block diagram, Fig. 3-6, shows the basic elements of
\n<\/span>the Time Base Generator. The Sweep Gating Multivibrator is <\/span>an electronic switch which turns the Disconnect Diodes on <\/span>and off. When the Disconnect Diodes are back-biased, the <\/span>Miller Runup begins to produce a sawtooth signal. A sample <\/span>of the sawtooth is fed back to the Sweep Gating Multivibrator <\/span>through the Holdoff Circuit. When the sawtooth <\/span>sample reaches a predetermined amplitude, the Sweep <\/span>Gating Multivibrator resets, switching the Disconnect Diodes.
\n<\/span>The Miller Runup then resets, forming the retrace or falling
\n<\/span>portion of the sawtooth. A sample of the sawtooth <\/span>retrace is fed back to the Sweep Gating Multivibrator, but is <\/span>delayed by the Holdoff Circuit. This delay prevents the <\/span>generator from beginning the next sawtooth until the circuits <\/span>have stabilized.
\n<\/span>In the following detailed circuit description, refer to the
\n<\/span>Time Base \u2018A\u2019 Generator schematic in the back of the manual.
\n<\/span>Unless otherwise stated, the STABILITY control is set <\/span>for triggered operation and the LEVEL control is set to mid- range.
\n<\/span>Quiescent Conditions
\n<\/strong><\/span>In the quiescent state; that is, when the generator is
\n<\/span>triggerable but no sweep is being generated, the circuit
\n<\/span>conditions are as follows:
\n<\/span>Sweep Gating Multivibrator<\/strong>\u2014V135A is conducting and
\n<\/span>V145A is cut off. The STABILITY control sets the grid voltage
\n<\/span>of\u00a0 V135A at about\u00a0 -50 volts. The approximate +25 volts at
\n<\/span>the plate is coupled to the cathode follower, V1358, and
\n<\/span>divided to about -55 volts at the grid of\u00a0 V145A. Since the <\/span>grid of\u00a0 V135A is about 5 volts more positive than the grid
\n<\/span>of\u00a0 V145A, V135A demands all available current from the
\n<\/span>common cathode circuit. With no current through V145A,
\n<\/span>its plate voltage is determined by the current through R147
\n<\/span>and the disconnect diodes.
\n<\/span>The voltage at the cathode at V135B (about +35 volts) <\/span>is coupled to the Crt Circuit to blank the appropriate beam.
\n<\/span>This same voltage is divided to about -25 volts and applied
\n<\/span>to the grid of\u00a0 V193A. Thus, V193A is cut off and the voltage <\/span>at the \u2018A’ + GATE OUT connector is zero.
\n<\/span>Disconnect Diodes<\/strong>\u2014V152A and V152B are conducting.
\n<\/span>V152A clamps the sawtooth output bus (the cathode of
\n<\/span>V161 B) at about -3.5 volts to provide a stable, repeatable,
\n<\/span>starting voltage for the sawtooth. V152B clamps the grid of
\n<\/span>V161A at about -2.5 volts.
\n<\/span>Miller Runup<\/strong>\u2014Since the grid of\u00a0 V161A is clamped at
\n<\/span>about -2.5 volts, the tube conducts heavily and the plate
\n<\/span>voltage is about\u00a0 +30 volts. The plate voltage is coupled <\/span>to the grid of\u00a0 V161B by the voltage divider, B167 and R167.
\n<\/span>This type of voltage divider reduces the dc level by about
\n<\/span>60 volts, but does not attenuate variations of the input voltage.
\n<\/span>Hold-Off Circuit<\/strong>\u2014V152C is conducting and V145B is cut <\/span>off. The voltage divider network, R177, R178, and R179,
\n<\/span>applies about -65 volts to the plate of\u00a0 V152C. Thus V152C
\n<\/span>conducts through R181 and sets the grid voltage of\u00a0 V145B
\n<\/span>at about\u00a0 -65 volts. V145B is cut off since its cathode <\/span>voltage is about\u00a0 -50 volts; the same as the voltage at
\n<\/span>the grid of V135A.
\n<\/span>Cycle of Operation
\n<\/strong><\/span>When a negative-going pulse is received from the Trigger
\n<\/span>Circuit at the grid of\u00a0 V135A, the Sweep-Gating Multivibrator <\/span>switches. Multivibrator action starts by V135A amplifying the <\/span>trigger pulse. The positive-going pulse at the plate of\u00a0 <\/span>V135A is coupled to the grid of\u00a0 V145A by the cathode <\/span>follower, V135B. V145A is driven into conduction, causing <\/span>a positive-going voltage change in the common cathode <\/span>circuit. This is positive feedback to the cathode of\u00a0 V135A <\/span>which further reduces its conduction. Thus, the original <\/span>action is compounded and the circuit rapidly switches.
\n<\/span>V145A conducts and V135A is cut off. V145A conducts more <\/span>heavily than did V135A. Therefore, the common cathode <\/span>voltage is about\u00a0 25 volts more positive than it was in the <\/span>quiescent state, and V135A remains deep in cut off after <\/span>the trigger pulse has ended.
\n<\/span>When V135A cuts off, the voltage at the cathode of\u00a0 V135B
\n<\/span>rises sharply from about +25 to about +128 volts. This <\/span>voltage step is coupled to the Crt Circuit and the + Gate <\/span>Out Cathode Follower. The crt is thus unblanked and the <\/span>beginning of the plus gate pulse is formed.
\n<\/span>With V145A now in conduction, its plate voltage has
\n<\/span>switched to a new level; about\u00a0 -6 volts. This negative
\n<\/span>voltage step cuts off conduction in the Disconnect Diodes.
\n<\/span>The current through the timing resistor, R160, is now diverted <\/span>and begins to charge the timing capacitor, C160. As the <\/span>timing capacitor charges, the grid of\u00a0 V161A goes negative.
\n<\/span>The greatly amplified positive-going change at the plate of
\n<\/span>V161A is coupled to the grid of\u00a0 V161B through the neon
\n<\/span>lamp, B167. The neon lamp lowers the dc level of the signal
\n<\/span>by about\u00a0 60 volts, but does not reduce the signal amplitude.
\n<\/span>The cathode of\u00a0 V161B provides the sawtooth output signal <\/span>plus feedback to two points within the time base generator.
\n<\/span>Feedback to the timing capacitor opposes the negative-
\n<\/span>going change at the grid of\u00a0 V161A. This action persists
\n<\/span>throughout the period of the sawtooth and limits the total
\n<\/span>change in grid voltage to less than one volt. Since the
\n<\/span>voltage drop across the timing resistor is held nearly
\n<\/span>constant, the current through the resistor is essentially a
\n<\/span>constant value. This constant current flows into the timing
\n<\/span>capacitor and the voltage across the capacitor increases at <\/span>a very linear rate. The rate of rise of the sawtooth is a function <\/span>of the RC time constant of the timing resistor and
\n<\/span>capacitor.
\n<\/span>An attenuated sample of the positive-going output <\/span>sawtooth is applied to the plate of\u00a0 V152C in the Hold-Off <\/span>Circuit. The steady rise in voltage at the cathode of\u00a0 V152C <\/span>charges the hold-off capacitor while raising the grid voltage <\/span>on V145B. When the sawtooth has reached about one-half
\n<\/span>its final amplitude, V145B begins to conduct. As the sawtooth <\/span>continues to rise, the cathode of\u00a0 V145B and the grid of\u00a0 <\/span>V135A also rise. V135A will begin to conduct when its grid <\/span>has risen about 20 volts. The plate voltage on V135A and <\/span>the grid voltage on V145A drop and the cathode current no <\/span>longer required by V145A is assumed by V135A. This positive <\/span>feedback rapidly drives V135A into heavy conduction <\/span>and V145A into cut off.
\n<\/span>The negative-going voltage step at the cathode of\u00a0 V135B
\n<\/span>blanks the crt and forms the end of the + Gate Out pulse.
\n<\/span>The positive going voltage step at the screen grid of\u00a0 V145A <\/span>is coupled to the appropriate vertical plug-in unit\u00a0 to cause
\n<\/span>a multi-trace plug-in unit, operating in the \u201calternate\u201d <\/span>mode, to switch channels.
\n<\/span>When V145A cuts off, its plate voltage rises sharply to
\n<\/span>about\u00a0 -3 volts and brings V152B into conduction. The grid
\n<\/span>voltage on V161A rises and its plate voltage drops, carrying <\/span>the grid and cathode of\u00a0 V161B with it. When the cathode of\u00a0 <\/span>V161B drops to about\u00a0 -3.5 volts, V152A conducts to clamp <\/span>the sawtooth output bus at that voltage level.
\n<\/span>A sample of the falling voltage at the cathode of\u00a0 V161B
\n<\/span>is coupled to the plate of\u00a0 V152C, cutting off its conduction.
\n<\/span>While the hold-off capacitor was charged through the diode,
\n<\/span>it must discharge through a large resistor, R181. This
\n<\/span>retarded discharge (holdoff) delays the fall in voltage at the
\n<\/span>grid (and hence, the cathode)\u00a0 of\u00a0 V145B. The STABILITY
\n<\/span>control voltage divider network cuts off\u00a0 V145B when its
\n<\/span>cathode drops to about\u00a0 -50 volts. Thus, V135A is reduced
\n<\/span>from a stale of heavy conduction to its original quiescent
\n<\/span>(triggerable) state.
\n<\/span>Triggerable pulses which may arrive at the grid of\u00a0 V135A
\n<\/span>while the sweep is in progress have no effect since V135A
\n<\/span>is already deep in cut off. When V135A is driven into <\/span>heavy conduction at the peak of the sawtooth, trigger pulses <\/span>still have no effect because their fixed amplitude is too low <\/span>to bring V145A out of cut off. The Hold-Off Circuit extends <\/span>this period of insensitivity and thus blocks the start of the
\n<\/span>next cycle until the circuits have stabilized. Hold off time <\/span>is required for stable triggering and is related to the timing <\/span>capacitor being used. The proper holdoff capacitor is <\/span>selected by the TIME\/DIV. switch (see the Timing Switch
\n<\/span>schematic).
\n<\/span>Special Component Functions<\/strong>\u2014C141 assures that the
\n<\/span>Sweep-Gating Multivibrator will switch rapidly from one
\n<\/span>conduction state to the other. R187 and R189 isolate the
\n<\/span>shunt capacitance of the unblanking cables from the
\n<\/span>Sweep-Gating Multivibrator so its switching speed is not degraded.
\n<\/span>C165 aids V161B in charging the shunt capacitance in its
\n<\/span>cathode circuit at the fastest sweep rates. C167 insures <\/span>that the voltage divider consisting of B167 and R167 will <\/span>have the proper frequency response. The SWEEP LENGTH <\/span>control, R178, is set during calibration for the proper
\n<\/span>sawtooth amplitude. D131 clips the positive-going portion of <\/span>the triggering signal and C130 bypasses it to ground.
\n $\"\"$
\n<\/span>STABILITY control<\/strong>\u2014Fig. 3-7 shows the relationship between <\/span>the voltage at the Sweep-Gating Multivibrator input grid and <\/span>the sawtooth output of the time base. Normally, the <\/span>STABILITY control is set near mid-range so the voltage at the <\/span>Sweep-Gating Multivibrator input grid will be at the level <\/span>represented by E_{2<\/sub> in Fig. 3-7. This voltage level is about 2 <\/span>volts above the trip level (E_{1<\/sub>) required to cause the multivibrator <\/span>to switch states. An incoming trigger from the Time <\/span>Base Trigger circuit will drive the grid below the trip level.
\n<\/span>The multivibrator will immediately switch states and a
\n<\/span>sawtooth cycle will begin.
\n<\/span>When the output sawtooth has reached about one-half of
\n<\/span>its final amplitude, the Hold-Off Cathode Follower begins to <\/span>conduct and raises the voltage on the Sweep-Gating Multivibrator <\/span>input grid. The voltage continues to rise until it <\/span>reaches the reset level represented by E_{3<\/sub>. At this level, the
\n<\/span>multivibrator resets to its previous state and the retrace <\/span>portion of the sawtooth begins. The falling voltage at the
\n<\/span>input grid of V135A is retarded by the Hold-Off circuit, but
\n<\/span>finally stabilizes at the quiescent level, E_{2<\/sub>. The entire circuit
\n<\/span>is then ready for the next trigger pulse.
\n<\/span>As you will note from the foregoing description and Fig. 3 7, <\/span>the stability voltage at the Sweep Gating Multivibratar
\n<\/span>input\u00a0 grid must be at the correct level for triggered operation <\/span>to occur. As the STABILITY control is turned
\n<\/span>counterclockwise, the quiescent voltage will become more positive <\/span>than E_{2<\/sub>. The amplitude of the trigger pulses will then be <\/span>insufficient to drive the grid through the trip level E<\/span>_{1<\/sub>. Since<\/span>the time base will not operate, this condition is referred to as \u201c<\/span>lockout\u201d.\u00a0 As the STABILITY control is turned clockwise, the <\/span>voltage becomes more negative than the trip level E_{2<\/sub>, and <\/span>the Sweep-Gating Multivibrator will switch without waiting <\/span>for a trigger pulse. As the sawtooth cycle thus initiated<\/span>carries the input grid of the multivibrator through the <\/span>retrace and hold-off period, the voltage will again fall <\/span>below the trip level. Thus, another cycle will be initiated.
\n<\/span>The sweep generation will repeat without the need for <\/span>trigger pulses as long as the voltage from the STABILITY
\n<\/span>control is sufficiently negative. This condition is referred to <\/span>as \u2018free run\u2019 and can also be obtained by setting the LEVEL
\n<\/span>control\u00a0 to the FREE RUN position (provided UPPER HORIZ. <\/span>DISPLAY is set to \u2018A\u2019 TIME BASE)\u00bb.
\n<\/span>\u00a7\u00a7\u00a7
\n<\/span>Il testo prosegue nella settima parte.
\n<\/span>Per consultare le altre schede dedicate a questo oscilloscopio esposto al museo MITI (su proposta di Fabio Panfili)<\/span> scrivere \u201c565\u201d su Cerca.
\n<\/span>Elaborazioni e testo a cura di Fabio Panfili.
\nPer ingrandire le immagini cliccare su di esse col tasto destro del mouse e scegliere tra le opzioni.<\/span><\/span>
\n
\n<\/span><\/p>\n}}}}}}}

<\/p>\n","protected":false},"excerpt":{"rendered":"

Oscilloscopio Tektronix Type 565. Sesta parte. Nell\u2019inventario D del 1956 si trova al n\u00b0 3747 e risulta acquistato nell\u2019agosto del 1964; vi si legge: \u201cSilvestar ltd. Milano. Oscilloscopio Tektronix mod. 565 matr 689. Dest. Elettronica \u20a4 1\u0387678\u0387600\u201d. Insieme alla fotocamera che \u00e8 al n\u00b0 3746, dove si legge: \u201cSilvestar ltd. Milano. Macchina fotografica Tektronix mod. … <\/p>\n