tvr-c3.doc

INSTRUCTIONS FOR USING THE

UNIVERSITY

CATHODE RAY OSCILLOSCOPE

MODEL TVR-C3

UNIVERSITY GRAHAM INSTRUMENTS PTY. LTD.

For all Measuring and Testing Instruments

5 NORTH YORK ST., SYDNEY 

APPLICATIONS .

The Model TVR-C3 is a small, truly portable oscilloscope. A new type of cathode ray tube, type DG7-32 together with miniature components have enabled a reduction in the weight and size of the instrument, whilst still offering the quality and features available in larger models.

This oscilloscope will be found quite suitable for TV servicing and general servicing in repair shops, laboratories and workshops. The selectivity curve of TV, RF and IF circuits can be displayed on the cathode ray tube screen in con­junction with a "Sweep Oscillator" and all adjustments and aligning can he done while actually observing their effect on the curve shape. Vertical amplifier response to 1 mc/s enables examination of synchronising and deflection waveforms. Other applications include checking audio amplifiers, broadcast receivers, tape recorder servicing, distortion measurements etc. A tape playback head can be directly attached to the vertical amplifier of the CRC and output checked, in­cluding supersonic bias.

CIRCUIT DESCRIPTION.

The circuit, shown at the rear, can be divided into four main sections - cathode ray tube, power supply, vertical amplifier and time base with attached horizontal amplifier.

The cathode ray tube DG7-32 employs electrostatic deflection, and focusing of the beam. It is designed to operate with a final anode voltage of about 500 and this H.T. supply is obtained from 500 volt winding on the transformer rectified by using a high voltage metal rectifier. Large capacity filter condensers are used to ensure a minimum of ripple voltage.  The final anole of the cathode ray tube is earthed and the rectifier provides a negative output which is applied to its cathode. A separate heater winding is provided for the tube, on the mains transformer to avoid a large potential difference existing between heater and cathode.

The sawtooth scanning voltages are applied in antiphase to the two horizontal plates of the tube and the use of push-pull output reduces trapezoidal effect of the trace, as short, low voltage cathode ray tubes have an inherent degree of trapezoidal effect.

Voltages under examination are applied to one vertical plate either directly or from the output stage of the vertical amplifier. The "Focus" control applies a varying degree or voltage to grid No. 2 and enables a sharp and fine trace to be obtained.

The "Intensity" control sets the DC level of the grid. Pulses are applied from the time base to achieve fly-back suppression. These pulses are applied through a frequency compensated network and the degree of fly-back suppression can be controlled by the Intensity control.

TIME BASE

The time base has six positions, five sweep ranges and an "off" position which

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disconnects the time base. In this position the tube can be used as horizontal amplifier or amplifier for external sweep. The five ranges cover frequencies from l5 c/s to 25 Kc/s and can be accurately adjusted by the potentiometer marked "Fine". All ranges are overlapping. The sawtooth waveform can be externally synchronised and the time base output is available at the "Horizontal Plate" socket at top of the instrument if required for external use.

A triode amplifier is provided for horizontal deflection giving a partial push-­pull effect for the deflecting plates. The tube can be used as a separate horizontal amplifier with or without internal time base.

All input sockets and controls are located on the front panel.  The top row comprises three combined sockets (the function of these is explained later, for connection to the vertical plate direct, the modulation grid of the cathode ray tube direct and the horizontal plate direct.

The purpose and location of controls is clearly labeled on the panel and is shown in Fig.2.

SPECIFICATIONS:

Power supply: 220 - 240, volts, 40-60 c/s.

Power consumption: 33W.

Amplifiers and time base H.T. = 250-375volts.C

Cathode Ray Tube E.H.T. = 560 volts.

Cathode ray tuba DG7-32, diameter 2¾". Green trace, sensitivity: 22V R.M.S. or 62V peak-to-peak/inch direct to plates. Horizontal sensitivity: 20V R.M.S, or 56V peak-to-peak/inch direct to plates. Input impedance directly to plates from front panel 3 megohms, 7 pf.

TIME BASE   Miller - phantastron time base with paraphase amplifier - push-pull deflection of trace when horizontal amplifier is used to extend the trace.

FREQUENCY RANGE: 15 c/s to 25 Kc/s.

Switched range control with tire base "off" in position 1.

Continuously variable frequency control.

Time base output available at the top right hand socket - "Horizontal Plate" - at medium or high impedance,

Flyback:  Degree of suppression controllable by "Intensity" control. Can be

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switched off by inserting a dummy plug into top centre socket (External Modulation) or external modulation can be applied at same place.

SYNCHRONISATION is of a lock-in type, design typical of "Miller" time bases, and is internally controlled. By plugging in a dummy plug this synchronisation can be disconnected, or external synchronisation applied in the vicinity of .5-2V.

VERTICAL AMPLIFIER

The vertical amplifier consists of two stages, being essentially flat from 15 c/s to 150 Kc/s plus or minus 1 db and 6 db down at 1 Kc/s with the gain control in "full gain" position.

A usable trace is available up to 1 Mc/s and an undistorted, output can be obtained up to a trace amplitude of 2¼ inches height.  Average gain is approximately 500.  Deflections sensitivity at full gain being of the order of 70mv R.M.S./inch.  The gain output is continuously variable - for both amplifier inputs- i.e. for              "V. Amp" input socket, and for the "V. Amp ÷10" socket.

HORIZONTAL AMPLIFIER

The horizontal amplifier consists of a single stage with fully variable gain control, Gain a proximately 10.

Essentially flat from 10-150 Kc              (plus or minus 1 db) with response 6 db down at 1 Kc/s with the gain control at "full gain" position. Maximum input at this setting l0V R.M.S. . (equals nearly twice screen width.) Deflection sensitivity 1.6V R.MS./inch. The amplifier is normally connected to the time base and works as a paraphase amplifier compensated to offset any non-linearity of the time base at high frequencies.

A spring handle is fitted to the top of the oscilloscope, folding flat if not in use.              The instrument is 42 inches wide, 8½  inches high, 11½ long.  Weight 14 lbs.

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