Telequipment_S51B_and_S51E.pdf part of Telequipment D1010 & D1011 s51_s51e_s51t.pdf, Full Manual for Telequipment Single Beam oscilloscope. text manual preview

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T E L E Q U I P M E N T

OSCILLOSCOPE TYPE S51B A N D S51E

All TelequipmenT instruments are the subject of continuous development and improvement, and, in consequence, may incorporate minor detail changes from the information contained herein.

TelequipmenT is a registered trade mark of TELEQUIPMENT LIMITED* 313 Chase Road Southgate London, N. 14. England. Telephone: 01-882 1166 Cables: TELEQUIPT LONDON N 14

CIRCUIT

DESCRIPTION

VERTICAL AMPLIFIER Vla and b form a The vertical amplifier consists of three double triodes. cathode coupled amplifier stage with RV6 acting as the gain control. The signal is taken from Vlb anode and drives the output stage V3 via cathode follower V2a. V3 consists of a long-tailed pair with the signal taken to V3a and the vertical shift applied to V3b. V2b acts as a low impedance HT supply for V1, also providing approximately 15OV for Y shift and timebase circuits. The signal at the anode of V3b is taken to the INT-EXT trigger switch. The HT supply for the trigger circuit, V4 and V5b is taken from a common resistor R15 in the cathode circuit of V3.

TRIGGER

CIRCUIT the S51B and one in the it to the grid of phase the phase splitter and via an integrating circuit pulses of a television

The trigger selection is performed by three switches in S51E; S2 selects the INT-EXT triggering signal and connects S3 selects the positive or negative output of splitter V4b. connects it to S4 which either passes the signal directly or to V4a. The latter position, TV FIELD, integrates the field

waveform and attenuates the line pulses allowing the time base to be triggered by the field sync pulses. From S4 the signal is fed to V4a and V5b which form a cathode coupled bistable switch, the switching level being adjusted by the grid potential of V4a. On the AUTO position the switch S5 is opened and the grid of V4a is returned to In the absence of a signal V4a and V5b oscillate at a frequency the grid of V5b. determined by the time constant R42 and C19, but as soon as any input signal between about 50Hz and 1MHz is applied to the grid of V4a, the self-oscillation The square wave ceases and the multivibrator synchronises to the signal frequency. appearing at the anode of V5b is differentiated, the positive pulse removed by MR7 and the negative pulse used to trigger the time base.

TIMEBASE & H O R I Z O N T A L

AMPLIFIER

V6a is the Mi l ler sweep generator, the speed of run down being controlled by S8 and the VARIABLE speed control. The Miller valve is keyed by V5a and V6b which together form a d .c. c o u p l e d multivibrator. In the rest position of the timebase, V5a is off and its anode potential is clamped by MR8 and 9. V6b is conducting. A negative trigger pu Ise from V5b This is The resulting rise in lowers the grid potential of V6b and hence that of the anode of V6a. coupled to the grid of V6a, so reducing the valve current. V5a.

screen potential developed across R65 is coupled via R54 and S6a to the grid of This causes V5a anode voltage to fall; which leads to regenerative action whereby V6b becomes quickly cut off and V5a hard on. When the run down has reached the point where the cathode voltage of V6b has fallen to near that of the grid, V6b starts to conduct and a negative pulse is applied to the grid of V5a. and V6b to conduction. The positive going voltage at V6b anode, developed during the sweep, is coupled via S6b to the modulator plate of the CRT, to provide trace unblanking. The STABILITY control RV49 serves to set the grid potential of V5a to the point just short of the free running condition of V5a and V6b. The linear sweep voltage at the anode of V6a is taken via R64, C41 and R73 to one grid of the horizontal amplifier V7, horizontal shift voltage is applied to the other grid and the output at the anodes drives the CRT X plates in push-pull. Transistor TR1 in the common cathode circuit, acts as a constant current source and provides a balanced output at the two anodes. An external signal may be applied through a connector at the rear of the instrument. In this condition, the timebase should be switched off with the V5a is then switched for use as a preamplifier, thesignal Cathode bias is provided by RV56, decoupled by C25. In order to keep the d.c. conditions correct, VARIABLE speed control. being applied to its grid. Regeneration again takes place driving V5a to cut off

The signal at V5a anode is coupled via V6b, acting as a cathode follower, and S6d to the horizontal output amplifier V7. anode is decoupled by C26. 10 V5a and V6b anodes are switched by S6b to the 150V HT supply and in addition V6b

POWER

SUPPLY

Silicon rectifiers MR1 and 2 in a voltage doubling circuit supply the various HT voltages via smoothing resistor R24. The negative EHT supply for the CRT and STABILITY control via R29 is provided by MR3, 4 and 5, C8, 9 and 11. CRT. The positive EHT supply is derived from MR6 and C12. C 12 is returned to the HT line. The negative end of

It is applied via voltage reference

1 n e o n s N and 2, in parallel with the BRIGHTNESS control, to the cathode of the

CRT Intensity modulation signals may be applied via Cl6 to the grid of the CRT. The interplate shield potential is adjusted by RV88 to the mean potential of the deflector plates for optimum geometry or freedom from bowing of the display. RV89 provides preset astigmatism adjustment and RV92, blanking, allows the beam intensity to be adjusted to a maximum by varying the first anode potential.

MAINTENANCE

ADJUSTMENTS

The simplicity of the circuitry of the S51 makes it an extremely reliable instrument, and for the most part servicing will be limited to the replacement of Valve replacement will have little effect on performance and defective va Ives. If for any reason the should not necessarily entail readjustment of preset controls. internal presets do require adjustment, the following detailed instructions will al low this to be done quickly and accurately. The case may be removed after unscrewing the two screws at the rear of the instrument.

INPUT ATTENUATOR & PROBE In order to adjust the input attenuator compensation a squarewave generator is required with a frequency of approximately 2kHz and whose output can be varied The rise time of the squarewave need not be particularly between 0.2 and 1OOV. Connect the squarewave generator to fast, but it must have a flat top and bottom. Set the input the input socket and adjust the output to approximately 0.2V. 1 attenuator to . and adjust the sweep controls so that 3 cycles of the squarewave Now carry out the following procedure step by step, adjusting are displayed. On each setting of the each trimmer to give a square corner to the squarewave. input attenuator the output of the squarewave generator should be adjusted to give a display of approximately 2-3 cm amplitude. Set VOLTS/CM to: .2 .5 1 2 5 10 Adjust C112 C111 Cl04 Cl08 Cl09 C105

If these adjustments have been carried out correctly the 20 and 50V/cm ranges are automatically compensated. In order to adjust Cl02 and 103 it is necessary to use a high impedance probe, Remove as these two capacitors only affect compensation when a probe is in use.

the squarewave generator from the input socket and plug in the high impedance probe, connect the output of the squarewave generator to the probe tip and set the

, input attenuator to .l, set the output of the squarewave generator to give approximately 2cm amplitude and adjust the probe trimmer to give a flat top to the wave. generator and adjust C102. and adjust C 103. squareNow switch the input attenuator to 1, readjust the output of the squarewave Set the input attenuator to 10, readjust the generator All other ranges will automatically be correct.

VERTICAL

AMPLIFIER

Adjustment of the high frequency compensation of the vertical amplifiershould only be carried out if a squarewave generator is available which is capable of producing an accurate squarewave at a frequency of about 250kHz with a rise time of less than 1OOns and which is known to be absolutely free from ring or overshoot. The compensation circuits in the vertical amplifier are extremely stable and, unless such a generator is employed readiustment is undesirable. Set the input attenuator switch to 0.1 and adjust the output of the squarewave generator to give a trace of approximately 2-3cm amplitude (the output frequency of the generator should be between 200 and 300kHz). L is adjusted to give a flat 1 topped squarewave with a fast -rise time, square corners and no overshoot.

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The only other variable on the vertical amplifier is the SET Y G A I N c o n t r o l , which should be adjusted with a signal of known amplitude with appropriate setting of the VOLTS/CM switch.

TRIGGER

CIRCUIT

The only adjustment necessary in the trigger circuit is an occasional resetting of the trigger sensitivity control RV48; this should be set so that the trigger circuit If any attempt Now will operate when the trace amplitude on the screen exceeds 2mm. inevitably result.

is made to increase the sensitivity beyond this point erratic operation will almost Connect a signal, say a 2kHz squarewave, to INPUT.
SO

set the input attenuator and squarewave generator to give a trace 2mm high and adjust the TRIG SENS control t h a t , at a critical setting of the TRIG LEVEL Reduce the trace amplitude to lmm and make control, the sweep will just trigger.

sure that the sweep will not trigger on this signal.

SWEEP GENERATOR & HORIZONTAL AMPLIFIER To make a complete readjustment of the sweep generator and horizontal amplifier, carry out the following procedure:Remove the lead to the modulator anode, pin 7 on the CRT. Set the TIME/ Now advance the BRIGHTNESS control until the spot at the CM switch to 1 O O ľ S . beginning of the trace may be seen. By adjusting C41 a small tail may be made to appear on one side of the spot or the other. The correct setting for C41 is the point at which this tai l just disappears into the spot. Reconnect the lead to the modulator anode on the CRT. Now set the TIME/CM switch to 100ľs and the VARIABLE speed to the CAL X GAIN should be at minimum and the trace centred by the X SHIFT posit ion . control. Connect accurately known 100ľs marker pulses or an accurate 1OkHz squareAs adjustwave to the input terminals and adjust RV72 for 1 pulse or cycle per cm. ment of RV72 wi I I cause the trace to move horizontally, it should be recentred using For greatest accuracy, calibration should be carried out over the X SHIFT control. the centre 4 cm of horizonta I trace. To set up the X amplifier, adjust X SHIFT until the start of the sweep is at the centre of the screen. Turn the VARIABLE speed control to the timebase off position and adjust trace position (RV56) so that the spot is in the centre of the screen. Feed Now adjust X GAIN until 5cm of trace is into X IN a sine wave of 0.5V P.-P. displayed. The X amplifier is now set to lOOmV/cm.

CRT CIRCUIT

Feed 0.5V P.-P. into both X and Y inputs, with VOLTS/CM at

. , and a 1

By varying the X and Y shifts, see that the trace diagonal line will be produced. If any bowing occurs, adjust interplate remains undistorted over the tube face. shield potentia I, (RV88), to straighten. Remove the X input and set TIME/CM to a convenient speed, adjust RV89, ASTIG, in conjunction with FOCUS for optimum trace definition.

Remove the Y input and reduce BRIGHTNESS, adjust RV92, BLKG, for maximum trace intensity. On tube replacement, the link across N2 is removed if the range of the BRIGHTNESS control is not adequate to cut off the beam.