Advance acoustic SG62B User manual

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Signal Generator
SG62B
Instruction Manual
ADVANCE ELECTRONICS LIMITED
INSTRUMENT DIVISION
ROEBUCK ROAD, HAINAULT, ILFORD, ESSEX, ENGLAND
TELEPHONE; 01-500 1000 TELEGRAMS’ ATTENUATE ILFORD
Manual Part No. 21709 ACL 3/68/200 Printed in England

Contents
SECTION 1Introduction 3
SECTION 2Specification 4
SECTION 3Operation 5
3.
1
Power Supply 5
2.2 Function Selection 5
2.3 Frequency Setting 5
3^4 Output Level 5
2,5 Output Termination 5
2,5 Connections to Points of High Potential 6
section 4Circuit Description 1
4.1General 7
4.2 Signal Generating Stages 7
4.2(a) Radio Frequency Signals 7
4.2(b) Audio Frequency Signals 7
4.2 Ancillary Stages 8
4.3(a) Power Supply Circuit 8
4.3(b) Attenuation Stages 8
4.4 Functional Description 8
4.4(a) C.W. Mode 8
4.4(b) Modulated Mode 9
SECTION 5Maintenance 10
5,7General 10
5.2 Valve Replacement 10
5,2 Oscillator Recalibration Procedure 10
5.3(a) Setting Up 11
5.3(b) Overall Recalibration 11
5.3(c) SettingUpforOptimumTrackingOver Any One Range 12
5.3(d) Adjustment of A.F. Modulation Frequency 12
5.3(e) Checking Output Level 12
SECTION 6Components List and Circuit Diagram 14
SECTION 7Guaratee andService Facilitie 16
Illustrations
Fig. 1Functional Diagram—Overall 7
Fig. 2Functional Diagram—Recalibration 10
Fig. 3Component Location Diagram 1
3
Fig. 4Circuit Diagram 15

Introduction Section 1
The Signal Generator SG62B provides asine wave output over the.
range of frequencies between 150kHz and 220MHz which includes
most radio and television bands. Avariable frequency Colpitts
oscillator provides the basic radio frequency output in six switched
bands which cover the complete range of the instrument. The fre-
quency calibration accuracy of this oscillator is within ±1 %of scale
indication. Facilities are provided for amplitude modulation of the
radio frequency signal to adepth of 30 %from afixed frequency audio
signal (400Hzj generated by aHartley type oscillator.
To enable the output level to be set an attenuator is included in
the output circuit.
The instrument requires asingle phase a.c. power supplv of 105V to
125V, MOV to 160V or 210V to 250V at 45Hz to 60Hz.
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Specification Section 2
Frequency Ranges
A150kHz to 500kH
B500kHz to 1.8MH
C1.8MHz to 6MH
D6MHz to 20MH
E20MHz to 70MH
F70MHz to 220MH
Frequency Accuracy
Within 1%of scale indication.
Output Level
Continuously variable up to lOOmV by means of the fine (output
voltage) and course (output voLTAGE/dB) attenuators. Level is
correct to control settings only at 120V and 240V input supply, and
varies approximately proportionally with supply fluctuations.
Accuracy of maximum output ±3dB (Ranges Ato E),
Accuracy of step attenuator ±(3dB+3pV)
Output Impedance
75 ohms.
Via TP2B pad; 37.5 ohms.
Modulation
The r.f. signal is available as acontinuous sine wave, or as an
amplitude modulated sine wave with amodulation depth of 30°/
±3dB,at400Hz±10%.
Audio Frequency
An audio frequency sine wave of 400Hz at lOV (nominal) is available
at high impedance when switched to “mod” operation.
Accessories Supplied
175 ohms. Termination Pad, type TP2B.
1Connector Cable R.F., type PL28.
IInstruction Manual Part No. 21707
Power Supply
Single phase 45Hz to 60Hz.
105V to 125V
140V to 160V
210V to 250V
Consumption
Approximately 25 W.
Dimensions (excluding handles)
Length 5Jin, (15 cm) Width llin (23 cm). Depth 74in (19 cm)
Weight
II lb (5 kg.)
Finish
Blue case with light grey front panel.
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4

Operation Section 3
3.7 POWER SUPPLY
The Signal Generator Type SG62B is supplied with the power trans-
former connected for 210V/250V operation. If the local supply is in
the 105/ 125V or 140V/ 160V range the connection of the red lead to
the power transformer should be altered as follows :
—
(a) 140V/160V Operation: disconnect the red lead from the 210V/
250V terminal on the transformer (T2) and reconnect it to the
adjacent terminal.
(b) 105V/125V Operation: disconnect the red lead from the 210V/
250V terminal and reconnect it to the next but one terminal i.e.
the terminal adjacent to the 140V/160V terminal.
No other alterations should be made to the transformer wiring or
damage may be caused to other components in the instrument.
The instrument is switched on by setting the function switch to
MOD or cw as required and allowing at least two minutes to elapse
before attempting to obtain astable output. The presence of the
supply at the primary winding of the power transformer will be
indicated by the supply neon indicator being illuminated.
3.2. FUNCTION SELECTION
Wfien the function switch is set to the mod position the output
available at the r.f. socket will be the selected r.f. carrier signal
modulated to adepth of 30 %by a400Hz audio signal. The output
at the A.F. socket will be the 400Hz sine wave at anominal amplitude
of lOV from ahigh impedance source.
When the function switch is set to the cw position the output at the
R.F. socket will be an unmodulated sine wave at the selected radio
frequency.
3.3 FREQUENCY SETTING
The required frequency is selected by setting the range switch to the
required band and adjusting the slow-motion drive to obtain the
frequency indicated on the scale.
3.4 OUTPUT LEVEL
The c.w. output signal level at the r.f. socket is selected by setting the
calibrated potentiometer output voltage, and the switch attenuator
OUTPUT voLTAGE/dB, to obtain required output level up to lOOmV.
3.5 OUTPUT TERMINATION
The termination pad type TP2B matches the output into any low
impedance load and eliminates standing waves in the r.f. connector
cable. The pad includes a75 ohms, resistor, from which the output
signal should be routed to the instrument under test via the shortest
practicable r.f. connector. The output can also be fed directly to a
load of 75 ohms.
5

Operation Section 3
3.6 CONNECTIONS TO POINTS OF HIGH POTENTIAL
Since r.f. output from the instrument has arelatively low impedance
pain to earth ablocking capacitor (e.g. 0.05pF at 400Vwkg)must be
connected between the output and the external load if the load is at a
high potential. If the chassis of the instrument under test is live (as
on an a.c./d.c. type broadcast receiver) capacitors must be connected
in series with both the output and earth return leads of the Signal
Generator.
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Circuit Description Section 4
4.1 GENERAL
As can be seen from the functional diagram, Fig. 1, and the circuit
diagram. Fig. 4, the circuit of the instrument is basically two oscil-
lators. These circuits provide the r.f. output and a.f. modulation
signals via an attenuator network which permits the required output
level to be selected. The description is therefore divided into three
main parts viz; the signal generating stages, the ancillary stages and a
functional description.
R.f.
Fig. 1Functional diagram -overall For service Manuals contact
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4.2 SIGNAL GENERATING STAGES Tei>oi844-35i694F^x>?ia44-3525M
/\1-1 j- r- enQumes^mauritron.co.uk
ici) Radio Frequency Signals
As was stated in the introduction the r.f. signals are generated
by aColpitts type oscillator circuit comprising VI band the
associated components Cl, C8, R6, etc. Modifications have been
made to the basic Colpitts circuit to enable the output signal to
sweep the full wide frequency range required from the instru-
ment. The modifications consist of five switched resonant
coupling circuits (L1-L5) and the ganged variable tuning capaci-
tor, Cl. Initially the frequency sweep of Cl is set by adjustment
of the trimming capacitor C6 and the maximum and minimum
frequencies in each range selected by adjustment of the trim-
ming capacitor and core in appropriate coupling circuit; thus
providing the necessary degree of tuning accuracy.
{b) Audio Frequency Signals
The a.f. signals at afixed frequency of 400Hz are provided from
the Hartley type oscillator circuit formed by the triode Via and
its associated components C9, R16, R17, etc. The anode/grid
coupling link via the auto-transformer T1 is decoupled to pre-
vent r.f. noise altering its resonant frequency. Since the tolerance
of the inductance in T1 and capacitance in C16 is fairly wide the
capacitor is selected to provide the 10% tolerance on the400Hz
signal
7

Circuit Description Section 4
4.3 ANCILLARY STAGES
(a) Power Supply Circuit
The incoming a.c. supply is fed to the power transformer, T2 via
apair of r.f. suppression filters (L14/C24 and L15/C25) and the
on/off section of the function switch, S2. Three outputs are
derived from the power transformer which are utilised as
tollows:
—
IfD r-m.s. output is half-wave rectified via the diode,
MRl, and fed through asmoothing circuit (C23A/B and
R20) to produce anegative earthed 140V d.c. supply with
low ripple content.
(2) The 6V r.m.s. supply is used as the heater voltage for the
double-triode valve, VI. This supply is heavily decoupled to
r.t. via L9, L13, and CI2, to prevent extraneous signals
from being fed back to the power transformer.
(3) The third supply is derived by auto-transformer action
from the 105/125V primary winding of T2 to provide the
energisation voltage for the neon supply indicator when
S2 IS set to any position other than off.
(b) Attenuation Stages
The attenuation stages are provided in the outout circuit of the
insyument to enable the operator to control the r.f. output level
and, if necessary reset the output level accurately. The at-
tenuation controls consist of acoarse, step-attenuator, output
voLTAGE/dB, and acontinuously variable fine attenuator
OUTPUT VOLTAGE. Switch S3 and its associated resistors R8 to
KI5 form the coarse attenuator circuit whilst the fine attenuator
is formed by the variable resistor RVl.
4.4 FUNCTIONAL DESCRIPTION
{a) C.W. Mode
This ^ode of operation is selected by setting the function
switch, S.2, to the c.w. position. In this condition the MOV ht
supply is fed directly to the anode circuit of the r.f. oscillator”
Vib, which functions in the manner indicated in sub-section 4.2’
Although the h.t. supply is also applied to the anode circuit of
Via this stage will not oscillate since only part of the auto,
transformer T1 is in circuit; thus, the output at the r.f. socket
will be unmodulated r.f and no output will be available at the
A.F. socket.
8

Circuit Description Section 4
4.4 FUNCTIONAL DESCRIPTION (continued)
{b) Modulated Mode
This mode of operation is selected by setting the function
switch S2 to the mod position. In this condition the MOV h.t.
supply is fed to the anode circuit of Vlb via the auto transformer
T1 ;thus, since T1 forms the anode/grid coupling circuit for Via,
the h.t. supply to Vlb will vary with the oscillatory action of Via.
The output available at the R.F. socket will be the selected r.f.
signal amplitude modulated at 400Hz to adepth of approxi-
mately 30 %. The 400Hz a.f. signal will also be available at the
A.F. socket. When the function switch is set to the off position
after having been set to one of the other positions the supply to
the power transformer is isolated. In addition asecond section
of the FUNCTION switch provides adischarge path for the
smoothing capacitors, C23A, and C23B via the triode Via: the
period of thermal run-down of Via is sufficient to allow the
capacitors to discharge completely.
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Maintenance Section 5
5.7 GENERAL
Access to the controls and circuit components, mounted on afront
panel and chassis assembly, is gained by removing the wrap-round
case after releasing the two securing clips at the rear of the instrument.
Side panels may be removed, when necessary, after extracting their
four securing screws. Access to the oscillator valve and components
IS gained by removing the screening can in which they are contained
(see Fig. 3).
5.2 VALVE REPLACEMENT
The oscillator valve VI is secured in its valveholder by means of a
retaining clip. Changing the valve does not normally affect the
frequency calibration, but if any frequency scale requires recali-
bration, the procedure described in sub-section 5.3 should be
followed.
5.3 OSCILLATOR RECALIBRATION PROCEDURE IWN wolviuc iviaiiudio v^uillaUl
MAURITRON TECHNICAL SERVICES
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Fig. 2Functional diagram -recalibration
10

Maintenance Section 5
5.3 OSCILLATOR RECALIBRATION PROCEDURE (continued)
(a) Setting Up
(1) Remove the instrument case and the screening can.
(2) Switch the instrument on and allow at least twenty minutes
to elapse before commencing recalibration.
(3) Connect the r.f. output socket on the Signal Generator,
via asuitably matched coaxial cable, to :
—
(a) Ahigh input impedance diode voltmeter calibrated in
arbitrary units
(b) Ahigh input impedance mixer unit with acrystal
controlled reference oscillator. The mixer output is
then connected to aloudspeaker via an audio amplifier
(See Fig. 2).
(4) Set the output voltage and the output voLTAGE/dB
controls to their maximum settings.
(b) Overall Recalibration
(1)Set the RANGE control to F.
(2) Set the scale cursor at 70MHz.
(3) Set the crystal controlled oscillator to TOMHz. output.
(4) Adjust the Frange inductance strip curvature until the
loudspeaker gives anull frequency response.
(5) Note the indication given by the diode voltmeter.
(6) Set the scale cursor at 220MHz.
(7) Set the crystal controlled oscillator to 220MHz. output.
(8) Adjust the main trimmer (C6) until the loudspeaker gives a
null frequency response.
(9) Note the indication given by the diode voltmeter.
(10) Using anon-conducting tool, adjust the spacing between
the vanes of the tuning capacitor C7 in order to achieve
good tracking at frequencies intermediate between TOMHz
and 220MHz.
(11) Note the indications given by the diode voltmeter at the
selected intermediate frequencies. Check that these indi-
cations, and the indications noted in steps (5) and (9) are
within 3%agreement.
(12) Repeat the procedures of steps (2) to (11) (inclusive) until
the required accuracy of calibration and tracking has been
achieved.
(13) Set the range control to A.
(14) Set the scale cursor at 150kHz.
(15) Set the crystal controlled oscillator to output 150kHz.
(16) Adjust the core of the Arange inductor (LI) until the
loudspeaker gives anull frequency response.
11

Maintenance Section 5
(17) Note the indication given by the diode voltmeter.
(18) Set the scale cursor at 500kHz.
(19) Set the crystal controlled oscillator to output 500kHz.
(20) Adjust the arange trimmers (Cl and C26) until the loud-
speaker gives anull frequency response.
(21) Note the indication given by the diode voltmeter. Check
that this indication agrees with the indication noted in step
(17) within 3%.
(22) Repeat the procedures of steps (13) to (21) (inclusive) for the
remaining ranges B, C, Dand Ein turn, adjusting the
appropriate inductor core (L2 to L5) and trimmer (C2 to
C5)in each case.
(23) Finally, with the screening can in place, repeat step (22)
making final adjustments.
(c) Setting Up for Optimum Tracking Over Any One Range
Repeat the test procedures of 5.3 (b) steps (1) to (11) (inclusive)
for the required range, adjusting the inductor core and trimmer
appropriate to that range.
(d) Adjustment of a.f. Modulating Depth
The resistor R16 can be specially selected to obtain amodulation
depth of 30% ib 3dB, at 400Hz ±10%. The selected value of
R16 should lie within the range 4.7kO to 9.1k^2.
(e) Checking Output Level.
The output level on all bands should be checked to be within
±3dB. This may be accomplished by using the Advance Milli-
voltmeter VM79, coaxial “T” probe PL60A and a75H load.
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Fig. 3Component Location Diagram
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Components List and Circuit Diagram Section 6
RES/STORS (Carbon 10% unless
specified^
Ref. Value Description Part No.
R1 560 9236
R2 lOOK 1270
R3 27K 868
R4 33K 3434
R5 22K 3433
R6 22K 3433
R7 39 iw 978
R8 750 5%iW 3442
R9 91 5%iW 3441
RIO 750 5%iW 3442
Rll 91 57oiW 3441
R12 750 5%iW 3442
R13 91 5%iW 3441
R14 750 5%iW 3442
R15 82 5%iW 3440
R16 6.8K Selected on Test 6319
R17 470 5%iW 1606
R18 IK 5%iW 10263
R19 56K 3435
R20
R21 IK Not used 3424
R22 120K 4407
R23 47 iw 1818
R24 22 iW 4419
RVl 100 Plessey type E10374
Ref. Value Description Part No
C23 16+1 64F 350V Electrolytic
Hunts JF413K 7014
^25) 5000pF3KV Erie K3500 11 /CD8 1514
C26 Wire Trimmer 10681
INDUCTORS
LI Band “A” Tuning RF594
LI ABand “A” Coupling RF594
L2 Band “B” Tuning RF595
L2A Band “B” Coupling RF595
L3 Band “C” Tuning RF596
L3A Band “C” Coupling RF596
L4 Band “D” Tuning RF597
L4A Band “D” Coupling RF597
L5 Band “E” Tuning RF598
L5A Band “E” Coupling RF598
L6-7 Band “F” Tuning Silver Plated Strip
L8 Band “F” Coupling Part of Wiring
L9-10 R.F. Choke Dubilier 666 11212
Lll R.F. Choke C173
L12 R.F Choke Dubilier 666 11212
L13 Supply Filter choke C95
L14-15 R.F. Choke Dubilier 666 11212
CAPACITORS (Mallard 20% 150V unless
specified) MISCELLANEOUS
N1 Indicator Neon 125V 1165
Cl-6 Wire Trimmer 10681 MRl Rectifier 3560
Cl 532+532pF Variable ganged 11589 SI Range Switch 10364
C8 50pF 20% Lemco 350V 1562 S2 Function Switch 10364
C9 0.04pF 792 S3 Attenuator Switch A78
CIO 0.04pF 792 T1 Transformer (Modulator) MT348
Cll 0.04pF 792 T2 Transformer (Supply) MT345/B
C12 0.04pF 792 VI Valve 12AT7 (ECC81) 7106
Cl3-1 5300pF
C16-18 0.04pF
Cl9-22 300pF
TCC LT/3 Feed thro’ 7099
20% 400VW1MAM 3398
TCC LT/3 Feed thro’ 7099
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14

I
I
L.
For Service Manuals Contact
MAURITRON TECHNICAL SERVICES
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Oxon 0X9 4QY
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Email:- [email protected]^
70-220 I50-S00
MHz
C
-40
6-20 %
MHz
D
St S2 S3

Guarantee and Service
Facilities Section 7
This instrument is guaranteed for aperiod of one year from its
delivery to the purchaser, for the replacement of defective parts
other than valves, semiconductors and fuses. Valves and semicon-
ductors are subject to the manufacturers guarantee.
We maintain comprehensive after sales facilities and the instrument
can, if necessary, be returned to our factory for servicing. The type
and serial number of the instrument should always be quoted, together
with full details- of any fault and the service required. The Service
Department can also provide maintenance and repair information
by telephone or letter.
Equipment returned to us for servicing must be adequately
packed, preferably in the special box supplied, and shipped with
transportation charges prepaid. We can accept no responsibility
for instruments arriving damaged. Should the cause of failure dur-
ing the guarantee period be due to misuse or abuse of the inst-
rument, or if the guarantee has expired, the repair will be put in
hand without delay and charged unlessother instructions are received.
OUR SALES, SERVICEANDENGINEERING DEPARTMENTS
ARE READY TO ASSIST YOUAT ALL TIMES.
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16
Manual Part No. 21709