Telequipment S51E, S51B Service manual

TELEQUIPMENT

OSCILLOSCOPE

TYPE

AND

S51E

S51B

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: [phone]
Cables: TELEQUIPT LONDON N 14

VERTICAL AMPLIFIER

CIRCUIT DESCRIPTION

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

V3 consists of a long-tailed pair with the signal taken to

shift applied to

V2b

acts as a low impedance HT supply for

15OV

resistor

TRIGGER CIRCUIT

for Y shift and timebase circuits.

The signal at the anode of
The HT supply for the trigger circuit, V4 and

R15

in the cathode circuit of V3.

V2a.

V3b.

V1,

also providing approximately

V3b

is taken to the INT-EXT trigger switch.

V5b

is taken from a common

Vla and b form a

V3a

and the vertical

The trigger selection is performed by three switches in the
S51E; S2
splitter
connects it to S4 which either passes the signal directly or via an integrating circuit
to V4a.
waveform and attenuates the line pulses allowing the time base to be triggered by
the field sync pulses.

bistable switch, the switching level being adjusted by the grid potential of
On the AUTO position the switch S5 is opened and the grid of
the grid of

determined by the time constant R42 and C19, but as soon as any input signal
between about
ceases and the multivibrator
appearing at the anode of
and the negative pulse used to trigger the time base.

selects the INT-EXT triggering signal and connects it to the grid of phase

V4b.

The latter position,

From

S3 selects the positive or negative output of the phase splitter and

TV FIELD, integrates the field pulses of a television

S4

the signal is fed to

V5b.

In the absence of a signal

50Hz

and

1MHz

V5b

V4a

and

is applied to the grid of

synchronises

is differentiated,

V5b

which form a cathode coupled

V4a

and

to the signal frequency.

the positive pulse removed by MR7

V5b

oscillate at a frequency

V4a,

S51B

and one in the

V4a.

V4a

is returned to

the self-oscillation

The square wave

TIMEBASE &

V6a

S8

and the VARIABLE speed control.

HORIZONTAL AMPLIFIER

is the Mi l ler sweep generator,

the speed of run down being controlled by

The Miller valve is keyed by

V5a

and

V6b

multivibrator.

In the rest position of the timebase,

clamped by MR8 and 9.

lowers the grid potential of

coupled to the grid of

V6b

is conducting.

V6b

and hence that of the anode of

V6a,

so reducing the valve current.

screen potential developed across

V5a.

This causes

whereby

V6b

becomes quickly cut off and

V5a

anode voltage to

R65

V5a

is coupled via R54 and

fall;

which leads to regenerative action

V5a

When the run down has reached the point where the cathode voltage of

has fallen to near that of the grid,

applied to the grid of

V6b

and

to conduction.

V5a.

The positive going voltage at

S6b

coupled via

to the modulator plate of the CRT, to provide trace unblanking.

V6b

starts to conduct and a negative pulse is

Regeneration again takes place driving

V6b

anode, developed during the sweep, is

The STABILITY control RV49 serves to set the grid potential of

point just short of the free running condition of

which together form a d

.c.

coupled

is off and its anode potential is

A negative trigger pu Ise from

V6a.

This is

The resulting rise in

S6a

to the grid of

hard on.

V5a

to cut off

V5a

to the

V5a

and

V6b.

V5b

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

VARIABLE speed control.

being applied to its grid.

V5a

The signal at

anode is coupled via

V5a
Cathode bias is provided by RV56, decoupled by C25.

timebase

is then switched for use as a preamplifier, thesignal

to the horizontal output amplifier V7.
V5a

and

V6b

anodes are switched by

should be switched off with the

V6b,

acting as a cathode follower, and

In order to keep the d.c. conditions correct,

S6b

to the 150V HT supply and in addition

S6d

V6b

anode is decoupled by C26.

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