{"id":14201,"date":"2019-10-25T17:39:20","date_gmt":"2019-10-25T15:39:20","guid":{"rendered":"https:\/\/www.istitutomontani.edu.it\/museovirtuale\/?p=14201"},"modified":"2024-01-08T22:00:41","modified_gmt":"2024-01-08T21:00:41","slug":"oscilloscopio-tektronix-type-515a-matr-005869-6a-parte","status":"publish","type":"post","link":"https:\/\/www.istitutomontani.edu.it\/museovirtuale\/oscilloscopio-tektronix-type-515a-matr-005869-6a-parte\/","title":{"rendered":"Oscilloscopio Tektronix type 515A matr. 005869 5\u00aa parte"},"content":{"rendered":"

$\"\"$
\nOscilloscopio a tubo catodico Tektronix Type 515A serial 005869. Quinta parte.<\/span>
\n\u00a0Della Tektronix, Inc. Portland, Oregon, Usa.\u00a0 Nell’inventario D del 1956, in data aprile 1961, al n\u00b0 1899 si legge: \u201dImp. Silvestar-Milano – Oscilloscopio Tektronix tipo 515A. Destinazione Elettronica. \u20a4 840000\u201d. <\/span>
\nIl testo continua dalla quarta parte.<\/span>
\n\u00a7\u00a7\u00a7
\n $\"\"$ <\/span>
\n\u00abSchmitt Multivibrator
\n<\/strong>The dc-coupled multivibrator, shown in the <\/span>time-base diagram, turns on the time-base <\/span>generator upon receipt of a negative trigger <\/span>from the trigger shaper, and holds off <\/span>subsequent trigger signals until after the sweep <\/span>is completed. The multivibrator consists of <\/span>V110A and V120 with both common-cathode <\/span>and plate-to-grid coupling. Plate-to-grid coupling <\/span>is by means of a cathode follower.<\/span>
\nIn the quiescent state V110A is conducting and <\/span>its plate is down. Cathode-follower V110B <\/span>holds the grid of V120B below cutoff through <\/span>voltage divider R115 , R116. Cathode-follower <\/span>V110B isolates the plate of V110A from the<\/span>
\nvarious loads, and thereby permits a faster<\/span>
\nstep.<\/span>
\nWhen the negative trigger pulse from the <\/span>trigger-shaper stage reaches the grid of V110A <\/span>it is coupled to V120B and V120B starts to <\/span>conduct. The multivibrator switches quickly <\/span>to its second state with V120B conducting <\/span>and V110A cut off. The biases and plate loads <\/span>are adjusted so that when V110A is conducting, <\/span>the grid of V120B is held below cutoff, and <\/span>when V120B is conducting the cathode of V110A <\/span>is held above cutoff.<\/span>
\nThere are thus two stable states, in either <\/span>of which the multivibrator will remain until <\/span>a signal of the proper polarity and amplitude <\/span>to the grid of V110A switches it to the other <\/span>state. To return the multivibrator back to<\/span>
\nthe quiescent state with V110A conducting, a <\/span>positive voltage is required at the grid of <\/span>V110A which is high enough to cause plate <\/span>current to flow. The positive voltage for returning <\/span>the multivibrator to its quiescent state <\/span>is supplied from the time-base generator when <\/span>it has completed its sweep.<\/span>
\nThe STABILITY and PRESET controls adjust <\/span>the grid voltage of V110A near the point of <\/span>free running.<\/span>
\nTime- Base Generator
\n<\/strong>The time-base generator is a Miller integrator <\/span>circuit. The circuit includes disconnect diodes <\/span>V150A and V150B, cathode-follower V160A, <\/span>timing capacitor C160 and the Miller tube, <\/span>V160B. In the quiescent state between sweeps, <\/span>the plates of diodes V150A and V150B rest <\/span>at -2.5 volts. Very little current flows through <\/span>V150B to the grid circuit of V160B, and the<\/span>
\ngrid of V160B rests at -2.5 volts. More current <\/span>flows through V150A so that its cathode is <\/span>about .5 volt lower at -3 volts. The timing <\/span>capacitor, C160, which is connected between <\/span>these two points, therefore has a charge of
\n<\/span>about .5 volt. <\/span>The grid of cathode-follower V160A is<\/span>
\nconnected to the plate of Miller tube V160B through <\/span>neon glow tube B160. The grid of V160A <\/span>therefore follows the plate changes of V160B <\/span>but remains 55 volts below the plate. Network <\/span>C161, R161, improves the risetime of the <\/span>circuit.<\/span>
\nThe -2.5 volt bias on the grid of V160B <\/span>places the tube in the class A region of its <\/span>operating characteristic, where the plate-to-<\/span>cathode voltage is inversely proportional to <\/span>the grid to cathode voltage. The plate rests <\/span>at about +55 volts. The negative step from <\/span>the multivibrator to the plates of diodes V150A <\/span>and V150B lowers the plates below their cathodes<\/span>
\nand they no longer conduct. The Miller-tube <\/span>grid, and the cathode follower are thus released <\/span>to seek their own voltage levels. The grid <\/span>of Miller tube V160B, which is returned to<\/span>
\n-150 volts through R150, starts negative. When <\/span>the grid starts negative the plate starts-positive <\/span>carrying cathode-follower V160A grid and <\/span>cathode positive. This raises the top end <\/span>of C160 positive which thus tends to prevent <\/span>the Miller tube grid from going negative.
\n<\/span>The gain of the Miller tube as a class-A <\/span>amplifier is so high that the plate signal <\/span>coupled back through charging capacitor C160 <\/span>keeps the grid voltage constant within a fraction <\/span>of a volt. Meanwhile, C160 is charging with <\/span>current through R150 from the -150-volt bus.
\n<\/span>Since the grid of V160B remains constant <\/span>within a fraction of a volt, the current through <\/span>R150 remains constant, and C160 thus charges <\/span>at a constant rate. As C160 charges the voltage <\/span>of the upper end therefore rises linearily.<\/span>
\nAny departure from a linear rise of the cathode <\/span>of cathode follower V160A will result in a change <\/span>in Miller-tube grid voltage in the direction <\/span>that will correct for the error. A bootstrap <\/span>capacitor, C165, increases the plate current <\/span>in V160B at the higher sweep speeds to help <\/span>maintain a linear voltage rise.
\n<\/span>The linear rise of the cathode of V160A <\/span>is used as the time-base sawtooth. Charging <\/span>capacitor C160 is selected by means of a step <\/span>switch, SW155, labeled TIME\/CM on the front <\/span>panel. Charging resistor R150 is also selected <\/span>by the TIME\/CM switch so that both the size <\/span>of the capacitor being charged and the current <\/span>charging the capacitor can be selected to cover <\/span>a wide range of sawtooth slopes.<\/span>
\nThe cathode of V160A continues to rise <\/span>linearly until a positive step from the <\/span>multivibrator, V120B, returns the disconnect diode <\/span>plates back to their quiescent state raising<\/span>
\nthe Miller tube grid. When the Miller tube <\/span>grid rises, its plate drops carrying cathode-<\/span>follower V160A with it until its cathode clamps <\/span>again through V150A at the quiescent level <\/span>of -2.5 volts. The Miller-tube plate will always <\/span>rest at about +55 volts after the sweep, because, <\/span>as V150A begins to conduct, its plate drops <\/span>slightly. This reduced plate voltage allows <\/span>the Miller-tube grid to go slightly more negative, <\/span>stopping the fall in plate voltage.<\/span>
\nSawtooth Amplitude
\n<\/strong>The positive step from multivibrator V120B, <\/span>which stops the sweep, occurs when a positive <\/span>voltage is delivered to the grid of multivibrator <\/span>V110A. The time-base sawtooth is applied <\/span>to the multivibrator through cathode followers <\/span>V140A and V140B from a tap on the cathode- <\/span>load resistor of V160A. This tap is adjustable <\/span>by means of potentiometer R156, labeled <\/span>Sawtooth Amplitude, a screwdriver adjustment.<\/span>
\nWhen the voltage of this tap is properly set, <\/span>the sawtooth will terminate when the spot <\/span>has passed the right-hand limit of the graticule.<\/span>
\nC130 on the grid of V140B retards the return <\/span>of V140B grid to the quiescent level after <\/span>the passage of the positive voltage. This prevents <\/span>any trigger signals from retriggering the <\/span>multivibrator until all other capacitances in the <\/span>circuit have had time to reach their quiescent <\/span>voltage levels. Proper sizes of capacitor C131 <\/span>are switched with the TIME\/CM switch so <\/span>that more recovery time is permitted for <\/span>the slower sweep rates and the least necessary <\/span>recovery time is allowed for the faster sweep <\/span>rates.
\n $\"\"$
\n $\"\"$
\n<\/span>Horizontal Amplifier
\n<\/strong>The time-base waveform passes through the <\/span>frequency-compensated positioning network, <\/span>R210, R211, to the grid of cathode-follower <\/span>V210B. This cathode follower provides the <\/span>necessary low impedance to drive the switch <\/span>capacitances and the second cathode follower, <\/span>V210A. In the NORM. position of the HORIZ. <\/span>DISPLAY switch, an attenuation network is <\/span>inserted between the cathode of the Input C.F., <\/span>V210B and the Driver C. F., V210A. In the <\/span>MAG. position of the HORIZ. DISPLAY switch, <\/span>this attenuator network is bypassed, so that <\/span>the amplitude of the input signal to the Amplifiers <\/span>is multiplied by a factor of five. In the EXT <\/span>position, the HORIZ. DISPLAY switch connects <\/span>the amplifier to the EXT. HORIZ. INPUT <\/span>binding post to display the signal applied to <\/span>this binding post.<\/span>
\nCathode-follower V210A applies the signal <\/span>to the output amplifier, V250A and V270A.
\n<\/span>The output amplifier, converts the signal for <\/span>push-pull application to the deflection plates. <\/span>R259 varies the degeneration in the cathode <\/span>circuits to set the gain of the amplifier. C260 <\/span>provides high-frequency compensation of the <\/span>output amplifier by reducing the high-frequency<\/span>
\ndegeneration. R214B provides horizontal <\/span>positioning when the HORIZ. DISPLAY switch is <\/span>in the EXT. position.<\/span>
\nThe waveform at the plates of the output <\/span>amplifier is applied to the crt horizontal-<\/span>deflection plates via cathode followers V250B <\/span>and V270B. Bootstrap capacitors C246 and <\/span>C272 increase the current in the output <\/span>amplifiers at the high sweep rates to improve <\/span>time-base linearity. Neon diodes B253 and <\/span>B280 protect the cathode followers from excess <\/span>grid to cathode voltage when the instrument <\/span>is first turned on.
\n $\"\"$ <\/span>
\nCALIBRATOR
\n<\/strong>The calibrator is a symmetrical multivibrator <\/span>with V550A and V550B connected so as to <\/span>turn cathode-follower V570 on and off as it <\/span>oscillates. During the negative pulse at <\/span>multivibrator V550A, the grid of the cathode follower <\/span>is driven well below cutoff , so the cathode is <\/span>at ground voltage. During the positive pulse <\/span>at the multivibrator, the plate is cut off and <\/span>rests slightly below +100 volts. The voltage <\/span>of the plate during cutoff is determined by <\/span>the setting of R560, part of a divider between <\/span>+ 100 volts and ground. R560 is a screwdriver <\/span>adjustment labeled CAL. ADJ.<\/span>
\nCathode follower V570 has a tapped, calibrated <\/span>voltage divider for its cathode resistor. When <\/span>the CAL. ADJ. control is properly set, the <\/span>cathode-follower cathode is at +100 volts when <\/span>V510B is cut off. The taps on the divider <\/span>provide eleven fixed calibrated amplitudes. <\/span>No internal connection from the calibrator <\/span>to the vertical-deflection circuits is provided.
\n $\"\"$ <\/span>
\nPOWER SUPPLY
\n<\/strong>Transformer
\n<\/strong>Plate and heater power for the Type 515\/515A <\/span>is provided by a single power transformer, <\/span>T600. The transformer has two equal 117-volt <\/span>windings that can be connected either in parallel <\/span>for 117-volt operation, or in series for 234- <\/span>volt operation.<\/span>
\nRectifiers
\n<\/strong>The ac voltage from the high-voltage windings <\/span>is rectified by bridge-connected full-wave <\/span>selenium rectifiers.<\/span>
\n-150 Volt Supply
\n<\/strong>All dc voltage furnished by the power supply <\/span>are regulated with the exception of the +360-<\/span>volt supply which is used only to supply circuits <\/span>which are insensitive to voltage variations.<\/span>
\nReference voltage for the regulators is <\/span>established by means of a gas-diode voltage reference <\/span>tube, V602. The voltage-reference tube determines <\/span>the grid voltage of a comparator amplifier, <\/span>V607, in the -150-volt supply.
\n<\/span>The grid potential of V607B is compared <\/span>with the voltage obtained from a divider, R616, <\/span>R617, R618, between the -150-volt bus and <\/span>ground. R617, labeled -150 ADJ., determines <\/span>the percentage of the total voltage that appears
\n<\/span>at the grid of V607A and thus determines the <\/span>total voltage across the divider.
\n<\/span>The voltage difference between the two grids <\/span>of V607 appears as an amplified error signal <\/span>at the plate of V607B. The amplified error <\/span>signal is dc coupled to the grid of the series-<\/span>regulator tube, V610. This dc-coupled error <\/span>signal controls the plate resistance of the <\/span>series regulator tube, changing it in the right<\/span>direction to compensate for any change in <\/span>output voltage. C613 increases the ac gain<\/span>
\nof the feedback loop to reduce the ripple.
\n<\/span>The screen of V607B has a small amount <\/span>of the ripple that exists ahead of the series <\/span>regulator tube connected to it through R605.
\n<\/span>The phase of this ripple is such as to reduce <\/span>the ripple of the -150-volt bus. This circuit <\/span>also improves the regulation in the presence <\/span>of line-voltage variation. R620 bypasses the <\/span>series tube to reduce the amount of load <\/span>current through it.<\/span>
\n+100-Volt Supply
\n<\/strong>The -150-volt supply serves as reference <\/span>voltage for the +100-volt supply. The voltage <\/span>at the tap on the voltage divider, R639, R640, <\/span>is applied to the grid of V631. The error <\/span>signal is amplified in V631 and applied to <\/span>the grid of V635B, the series-regulator tube, <\/span>R633, at the screen of V631, reduces ripple <\/span>and improves the regulation of the supply. <\/span>C636 increases the ac gain of the feedback <\/span>loop.
\n<\/span>+300-Volt Supply
\n<\/strong>Rectified voltage from terminals 8 and 9 <\/span>of the power transformer is added to the <\/span>voltage supplying the +100-volt regulator to <\/span>provide about 400 volts for the +300-volt <\/span>regulator and other points in the instrument <\/span>which do not ned a regulated voltage. The <\/span>+300-volt circuit is similar in operation to <\/span>the + 100-volt regulator.
\n $\"\"$ <\/span>
\nCRT CIRCUIT
\n<\/strong>High-Voltage Supply
\n<\/strong>Accelerating voltage for the cathode-ray tube <\/span>is obtained by rectifying a 60-kc voltage <\/span>produced by a vacuum\u2014tube oscillator. V705 is <\/span>the oscillator tube with the primary of T701 <\/span>serving as a tapped inductor. Rectifier V720 <\/span>supplies -1675 volts to the crt cathode and V721 <\/span>supplies +2325 volts to the post-acceleration <\/span>helix to provide a total acceleration voltage <\/span>of 4000 volts.
\n<\/span>High-Voltage Regulator
\n<\/strong>A divider from the crt cathode to the +300-<\/span>volt bus applies a sample of the negative <\/span>accelerating voltage to the grid of V710B. <\/span>R741 varies the voltage at the tap to adjust <\/span>the high voltage. The -150-volt supply,<\/span>connected to the cathode of V710B, serves as <\/span>a reference voltage. The amplified error signal <\/span>at the plate of V710B is applied to the grid <\/span>of the shunt regulator tube, V710A. The shunt <\/span>regulator tube determines the screen voltage <\/span>of the oscillator tube and thus controls the <\/span>oscillator output voltage.
\n<\/span>If, for example, the output voltage becomes <\/span>too high, the regulator reduces the voltage <\/span>on the screen of the oscillator tube. The <\/span>output voltage of the oscillator decreases and <\/span>the output voltage is corrected.<\/span>
\nUnblanking
\n<\/strong>The crt control-grid voltage is produced <\/span>by a winding and rectifier, V724, similar to <\/span>the cathode supply but insulated from it. The <\/span>positive end of the control-grid supply is <\/span>connected to the unblanking cathode follower.<\/span>
\nWhen the unblanking pulse is produced at <\/span>the cathode of the unblanking cathode follower, <\/span>it drives the whole grid-voltage supply with <\/span>it so that the pulse appears at the crt grid. <\/span>Since this is a dc connection, the unblanking <\/span>pulse can have any duration with no change in <\/span>grid voltage. The INTENSITY control, R731, <\/span>varies the bias on the grid to determine trace <\/span>brightness.
\n<\/span>CRT Geometry Control
\n<\/strong>The second-anode voltage required for best <\/span>linearity at the extremes of deflection may <\/span>vary somewhat between tubes. R753, labeled <\/span>GEOM. ADJ. on the chassis, permits this
\n<\/span>voltage to be adjusted\u00bb.<\/span>
\n\u00a7\u00a7\u00a7
\n<\/span>Per consultare le parti dedicate a questo oscilloscopio scrivere: \u201c515A\u201d su Cerca.<\/span>
\nFoto di Claudio Profumieri, elaborazioni, ricerche 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><\/p>\n

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

Oscilloscopio a tubo catodico Tektronix Type 515A serial 005869. Quinta parte. \u00a0Della Tektronix, Inc. Portland, Oregon, Usa.\u00a0 Nell’inventario D del 1956, in data aprile 1961, al n\u00b0 1899 si legge: \u201dImp. Silvestar-Milano – Oscilloscopio Tektronix tipo 515A. Destinazione Elettronica. \u20a4 840000\u201d. Il testo continua dalla quarta parte. \u00a7\u00a7\u00a7 \u00abSchmitt Multivibrator The dc-coupled multivibrator, shown in … <\/p>\n