Marconi CR.100 Release Note

AM"

0 ikT
; 
1 - 4
12._
RECEIVER
Type CR.100
TECHNICAL HANDBOOK
No. T 1868/1
NorE.—The photographs, drawings and letterpress used in this handbook are copyright
Maicom
MARCONI'S WIRELESS TELEGRAPH COMPANY LIMITED
Head Office: Marconi House, Chelmsford • Telephone: Chelmsford
3221 •
Telegraphic Address: Expanse, Chelmsford

RECEIVER TYPE CR. 100/2.
A.
Fine and Coarse Tuning Controls.
E.
H.F. Gain Control.
B.
Band-Change Switch.
F.
L.F. Gain Control.
C.
Aerial Trimmer.
G.
Beat Frequency Oscillator Control.
D. Pass-band Switch.
H.
Operational Switch.

DATA SUMMARY.
TYPE ..
FREQUENCY RANGE . .
SUPPLY REQUIREMENTS
Self-contained Communications Receiver of superheterodyne type
with A.V.C. for use on C\V or Phone reception.
60 kc/s to 420 kc/s
500 kc/s to 30 Mcls
• '  in 6 bands.
• •
(A) D.C. Supplies.
(1)
H.T. and L.T. Batteries.
H.T. 250 volts 100 mA. reduced to
160 Nolts 60 mA. if desired.
L.T. 6 volts 4 Amps.
or
(2)
Battery and Rotary Converter.
6 volts 8 Amps. total supply.
(B) A,C.
Supplies.
200/250 volts 50 c/s. 85 watts.
RECEIVER INPUT 
. .  .. 
100 ohms, balanced or unbalanced, or high impedance aerial.
SENSITIVITY . .

. . 
. . 
For 20 db signal-to-noise ratio on C.W.

(Average Receiver)

60 kc/s to 11 Mc/s. 1 to 2µV.
11 Mc/s to 30 Me/s. 1.5 to 4
µV.
VALVES 
.. 
. .  . . 
See page 9.
RECEIVER
OUTPUTS
Loudspeaker (3 ohms or 1,000 ohms) 2 watts maximum, approx.
Line (600 ohms) of the order of 2 mW.
Phones (high or low resistance) depending on impedance of Phones
and Receiver Edition.
MODIFIED EDITIONS

A number of Editions exist carrying modifications to suit the needs
of various Services, the principal models being CR. 100, CR. 100/2,
CR. 100/4, CR. 100/5, CR. 100/7, CR. 100;8 and CR. 100;8 Mod.
WEIGHT AND DIMENSIONS ..

Dimensions overall : Width 16 in ; Depth 161 in ; Height 12+ in ;
Weight 82 lb.

MARCON/
TYPE CR. 100 SERIES
OF RECEIVERS
SECT.ION 1.
G ENE't AL CHARACTERISTICS.
The receiver when operated from an A.C. supply is self-contained. It combines extreme
flexibility with high sensitivity and select-y:7.y, and is equally suitable for providing good quality speech
output at loudspeaker level as for the recep'..ion of C.W. signals under difficult conditions. it may be
operated from Batteries or Rotary Converter if desired.
SALIEi , ir FEATURES.
(1) Suoitieily and Image Protection.
By the use of two stages of high frequency amplification preceding the mixer, great sensitivity
and prctection against interference on image frequencies are obtained. image protection is of the
order of 30 db. (30 to Oat 23 Mc/s, and is greater than 60 db. (1,000 to 1) on frequencies below 11 MO.
(2)
Se!ectifi4 (Variable).
Protection against adjacent channel interference is made high by the use of a crystal gate and
three stages of Intermediate Frequency Amplification employing coupling circuits of high Q. A low
frequency filter preceding the output valve can be used to reduce further the pass-band width to 100
cycles if desired.
(3)
Automatic Volume Cont.:ol.
A.V.C. may be used on both phone and C.W. reception, and a suitable delay voltage and time
constants have been provided.
(4)
CLI:brF.tion and Log Bing Scales.
Easy tuning and accurate re-setting to any known frequency are ensured by the iliuminaLeci
scale co'dbiated directly in frequency, and the separate Logging Scale which has a high discrimination
and is driven from the same control spindle.
(5)
Side-Tone Facility.
Facilities are provided on certain models for muting the receiver during transmissions from
associated equipment.
( 1 )

(in
O
O
SECTION 2.
OPERATION.
Assuming that the receiver has been correctly installed the following instructions give all the
information essential for its correct use. Most of this information is also to be found in concise form
on a bound card supplied with later receivers.
Fig. 1. The numbered controls correspond to the numbers in brackets below.
PRELIMNARY ADJUSTMENTS FOR OPERATING THE RECEIVER.
(1)
MAINS SWITCH to ON. Dial lamps should light up. Allow a few minutes for warming up,
and longer if possible. This switch is not in circuit if operating the receiver from batteries.
(2)
OPERATIONAL SWITCH to " C.W.—A.V.C."
(3) PASS-BAND SWITCH to " 3,000 cis."
(4) H.F. GAIN at or near maximum clockwise.
Fig. I. Panel Controls.
L.F. GAIN adjusted to give a comfortable level of noise in phones or loudspeaker.
BAND-CHANGE SWITCH to the frequency band required.
TUNING. Adjust the pointer on the calibration scale to the desired frequency by the larger tuning
knob, and rock the smaller knob
slowly,
about one revolution on either z,ide, until the carrier of
the wanted station is heard. If RiT (telephone) is to be received change the Operational Switch (2)
to " MOD—A.V.C." and retune slightly if necessary.
B.F.O. Do not use the B.F.O. for fine tuning. When the receiver has warmed up (15 minutes
or longer if convenient) this should be adjusted and thereafter not varied, except for occasional
checking. See General Notes below.
AERIAL TRIMMER. If signals are weak this should be adjusted for best results. The optimum
setting for any frequency in use is found by reducing the H.F. Gain to a level at which strong
incoming signals do not sump the amplifiers or work the A.V.C., and then adjust for maximum
signal strength or maximum 1st circuit noise. The setting is more eritieed and important at the
high frequency end of the band in use.
( 2 )
(5)
(6)
(7)
(8)
(9)

GENERAL NOTES ON OPERATING THE RECEIVER.
Adjustment of Beat Frequency Oscillator.
To enable full use to be made of the selectivity of the receiver the B.F.O. must be accutately set
to give the optimum beat note of about 1 kcfs in the phones when the receiver is accurately tuned to the
signal. A convenient method of finding this setting is to make use of the characteristics of the L.F.
Filter, which is adjusted to have maximum response at this frequency. Proceed as follows : After
the preliminary warming up period put the Pass-band switch to 100 cis, the Operational switch to
C.W.--MAN and both gain controls at or near maximum so as to have a high level of receiver noise.
Adjust to a frequency where no signals are received, or disconnect the aerial. For maximum receiver
noise choose the high frequency end of Band 4. Rotate the B.F.O. Control knob to one of the points
at which the maximum rinning noise is heard, and leave it in this position. Checks should rarely be
necessary if the receiver is left switched on for long periods.
Use of Pass-Band Switch.
Once the wanted signal has been found the operator should endeavour to use a narrower pass-
band so as to get greater protection from interference. A very slight and careful readjustment of tuning
may be necessary when switching to the narrower pass-bands.
6,000 c/s Pass-band. Gives best intelligibility of speech, and makes tuning broader, but can only
be used when signals are strong and there is little interferenee. Used for C.W. signals only
in exceptional citcumstances.
3,000 c/s Pass-band. Better selectivity and less background noise. Recommended for use
on speech and when searching.
1,200 c/s Pass-band. High selectivity. Not used on speech. Useful chiefly on Bands 4, 5
and 6.
300 c/s Pass-band Higher selectivity. Used on C.W. only, chiefly
on
17.!:vids 1, 2, 3 and 4.
Can be used with care on Band 5, but not recommended for use on Band 6.
100 cis Pass-band. Hi Lest possible selectivity. For use on C.W. only, chiefly on Bands 1
and 2. If used on Bands 3 and 4 greater care in tuning is demanded as I the correct setting
of B.F.O. becomes increasingly important. Not recommended on Bands 5 and 6.
The narrowest pass-bands can only be employed where the frequency of the transmitted signal
is reasonably constant, and the speed of sin-nallin.
,
relatively low.
Vnen receiving C.W. on the broad pass-bar;ds and tuning through zero bmt it will be found that
the signal is equally strong on both sides, but en narrower pass-bawds one side will give a stronger
note than the other. The weaker signal may even be inaudible. Always tune to the stronger of the
two.
Should a signal be tuned-in on a wide pass-band and the wrong side of zero beat be selected,
the signal will probably be lost if the operator decides to change to a narrow paso I:and. Because of
this and the difficulty of distinguishing the stroneer signal it is recommended that the 6 kc/s pass-band
should not normally be used when tuning-in or searching for a C.W. signal.
Use of A.V.C.
The use of A.V.C. will be determined chiefly by the conditions prevailing and the shill of the
operator. It is given as a general rule,however, that A.V.C. should always be 
except whore the
wanted signal is weak and in danger of being lost because the gain has been reamed by the at tion of a
strong interference on the A.V.C. diode. Examples of this are peaky types of static, and pulse trans-
missions.
The II.F. Gain must be controlled ?nanually when transmitting on the same frevency, wiless the
receiver is being muted by the Side Tone Facility (as in the Type CR. 100/2
receiver) or other effective
device.
On C.W. the A.V.C. is given an increased recovery tine-constant. This will tend to broaden
the apparent selectivity when searching tnrousgh strong signals, and thus make tuning slower. To
switch off A.V.C. put the Operational Switch to MAN
( 3
)

Use of Gain Controls.
The relative positions of H.F. and L.F. gain controls will depend largely on whether the operator
is controlling the gain manually to prevent overloading of the H.F. and I.F. amplifiers or relying on the
A.V.C. to do it. The rule laid down for general guidance is
On C.W.--A.V.C..kH.F. Gain Control at maximum, except for very strong signals.
or MOD.—A.V.C. f L.F. Gain Control as desired.
On C.W.—MAN. H.F. Gain Control as desired.
or MOD.--MAN.
f L.F. Gain Control at approximately mid position.
" Off " Position of Operational Switch.
Frequency drift of the oscillator due to temperature fluctuation is reduced to a minimum if the
receiver is left switched on for long periods.
During short stand-by periods the H.T. to certain stages may be cut off by putting the Operational
switch to the OFF position.
Use of Logging Scale.
Fig. 2. Logging Scale.
This scale is not for reading frequency directly but for noting how to reset the tuning control
to a station which has once been found. Some slight allowance for initial drift should be made if the
receiver has not been running for 2 hours or more.
The main divisions 0 to 25 are read on scale " A " and sub-divisions on scale " B." 1 he example
shows a reading of 12-61.
(4)

SECTION 3.
TECHNICAL DESCRIPTION.
(A) ELECTRICAL.
CIRCUIT ARRANGEMENT. (See Drg. WZ.1943, page 47.)
Two signal frequency stages of amplification employing variable-mu valves arc used before
the mixer valve, which is of the triode hexode type. The triode section is not used, and the frequency
change oscillator is a separate valve. The mixer output voltage at the intermediate frequency of
465 kc/s ± 2 kc/s is applied to the I.F. amplifier embodying three stages, with suitable couplings and
a crystal gate for varying the band width. The third T.F. amplifier operates a double-diode-triode
incorporating the signal detector, the automatic volume control rectiner and the 1st audio frequency
amplifier. An independent beat frequency oscillator is provided for continuous wave reception and is
coupled to the signal detector.
An output stage and the mains rectifier valve and associated circuits complete the circuit plan.
Aerial Input, Signal Frequency Circuits and Mixer.
The overall gain of the signal frequency stages does not vary greatly between bands, and is
sufficient to make shot noise from the first valve greater than that geeerated by the mixer valve. Up
to a frequency of about 11 Mc/s the dynamic impedance of the first tuned circuit is high enough to
ensure that thermal agitation noise from this circuit exceeds valve noise, but on Band 6 the circuit
noise has fallen below valve noise, and the sensitivity is then limitcd by the first valve noise alone.
The feeder or dipole connections are taken via double-pole contacts on the aerial section of
the Band-change switch to the low impedance winding of the aerial coupling coil. In the case of the
Types CR. 100, CR. 100/4 and CR. 100/7 receivers the input is suitable for a balanced input if desired,
there being two terminals marked " D.' For the Types CR. 100/2, CR. 100/5 and CR. 100/8 receivers,
one end of the coupling coil is earthed and the other connected to a coaxial socket marked " D."
The coupling is designed to present an impedance of approximately 100 ohms on all bands. The
secondary winding with the rear section of the main tuning condenser and the aerial trimmer condenser
in parallel form the grid circuit of the first amplifier.
The aerial socket or terminal " A " is connected to the top of this circuit through a capacity
of 10 pf, and a static leak of 2 megohms to earth is provided.
The grid connections of signal frequency and 1st Oscillator valves contain stabilizing resistances,
the value being 10 ohms for V1,
t
'V2 and V3, and 50 ohms for V4.
The rear plate of the rotor of the grid circuit Band-change switch short-circuits the idle
inductances while the front plate selects the active one.
The bottom of the grid circuit of the two Signal Frequency Amplifiers and the first two inter-
mediate Frequency Amplifiers is joined to the A.V.C. line through a .30,000 ohms resistance, the top
end of which is decoupled by a condenser of 0.1 ill
, " to earth. The &coupling condensers, both for
grid and anode circuits of Signal Frequency Stages are situated in the P..
..F. Coil Astembly,
The cathodes of all signal frequency and intermediate frequency valves have series resistances
of 400 ohms or the preferred value of 390 ohms ± 20 per cent., and are decoupled by 0.1 tiF
condensers to chassis.
The screen grid voltage of signal frequency amplifiers and other Salves is taken from a line fed
from a voltage divider and is of the order of 80 volts. Each valve Las its own screen grid decoupling
resistance and condenser.
The coupling from the first to second amplifier is by the conventional untuned anode—tuned
grid transformer, the anode being decoupled from the H.T. supply by a resistance of 2,0
1
)0 ohms and
0.1 aF condenser.
Each grid circuit inductance is fitted with a trimmer conde aser. All inductances in the coil
pack have adjustable iron dust cores. The second signal frequency str se is similar to the first and drives
the 1st grid of the mixer. The mixer cathode resistance is connected to earth and the hottom of grid
circuit is also earthed ; there is therefore no manual or automatic control of bias on this valve. The
triode anode of the X66 is earthed.
(5)

Oscillate)? aad Into rnet"ate Frequency Circuits.
A KTW.62 valve coanecred as a triode and having a tuned grid circuit mutually coupled to an
untum4 anode coil serves as the frequency change oscillator. The oscillator operates at a frequency
higher than the sirs al fr-ttaanicy on all bands. Series tracker condensers are contained in the coil
pack in addition to the meal decoupling condensers. On the three lowest frequency bands variable
trimmer condensers ar. uttad to the oerifiator inductanc,s, but on Bands 4, 5 and 6, where very snveil
values of capacity are required, fixed capacitors are connected instead, the required value being
determined on test.
The tuned anocla circuit of the mixer is decoupled from the H.T. supply and forms the first
side circuit of the cry.-.t4 resonator. The second side circuit is also tuned and is coupled to the 1st
interrayliate fraquency
vane.
The crystal whose frequency may be between 463 kcis and 467 kcis,
is neutralised, a fraction of the voltage present in the 2nd side circuit being fed back into the 1st side
circuit in the correct phase. The neutralising condenser is situated in I.F.1 assembly and the crystal
is moanted in I.F.2 assembly, The crystal is not in circuit when using the 3,000 cis and 6,000 cis
positions of the Pass-band switch.
The normal band-width with the crystal in circuit is 1,200 cis. By switching the condenser C.43
(value 7 pF) from the first to the second side-circuit and altering the phase and impedance the band-
width is reduced to 300 cis.
The couplings between the three intermediate frequency amplifiers consist of loosely coupled
tuned transformer of high Q, both primary and secondary coils having variable permeability tuning
and fired value capacitors. A si all, tightly couplet: aueitiary coil is introduced in series with the
secondary of the I.F. t: ansformers, 1.F.3 and I.F.4, when the Pass-band switch is placed to 6,000 c/s.
The rain of the 
amplifiers is of the order of 28 db per stage (25 to 1). The conversion gain
of the mixer is about 16 db (6 to 1).
I.F. Sensitivity ft sues will be found in Section 5, page 30.
The selectivity switches S.10, S.11, S.12 and S.15 in Diagram WZ.1943, page 47, are all operated
by a common spindle.
All switches are shown on the diagram in the counter-clockwise pcsition.
Signal ratect.or
 A.V.C. Rem tiler.
The signal detector is driven from the secondary of the last I.F. circuit, and works into a series
connected load of 0.3 M fI with suitable low-pass filtering components, a portion of the rectified
voltage being applied to the L.F. gain control potentiometer via a capacity of 0.1 aF. The slider of
the potentierneter is connected to the grid of the triode section of the DH.63 valve and the bottcra is
tapped on to a suitable biasing point of the cathode resistance, giving a voltage of 1.8 veils negative
with respect to the cathode.
The auto-gain voltage is derived from the second diode of the DH.63 driven from the anode of
the 3rd I.F. valve via a capacitor of 100 pF. The A.V.C. diode load of 0.5 M 0 is in shunt with the
valve. In order to have the necessary delay the cathode is biased positive by about 16.8 volts relative
to the anode. Suitable decoupling is provided, and an additional capacity of I al 7
for increasing the
recovery time constant is introduced when the Operational switch is placed to C.W.
The time constant is 0.1 sec. on MOD, and 1.0 sec. on C.W.
Beat Frequency Oscillator.
The B.F.O. is of the electron-coupled Colpitts type, and is coupled to the signal detector through
a capacity of 30 pF. Tie core cf the inductance is adjustable as in the I.F. circuits, and a variation of
several kilocycles above and be'ow the intermediate frequency is obtained by the variable condenser
which is under the control of the operator. The correct adjustment of the B.F.O. condenser is a
matter of importance when using narrow pass-bands and is dealt with in Section 2, page 3.
( 6 )

Audio Frequency Amplifier.
The triode section of the DH.63 is resistance capacity coupled to the grid of the output tetrode,
KT.63. A band-pass filter having maximum response at a frequency of about 1 kc/s and a total band-
width of 100 c/s is inserted here when the Pass-band switch is put to " 100 c/s."
The gain of the amplifier at 1 kc/s is not reduced by the insertion of the filter. Suppression of
high-frequency voltages is attained by the use of capacitors in shunt with the two audio frequency
amplifier valves. Low frequency stability is ensured by adequate decoupling in the H.T. supply to
the DH.63 stage.
The various outputs are obtained through a multi-ratio transformer. The slope of the load
line, which should be of the order of 5,000 ohms, is determined by the loudspeaker, the line and phone
outputs having negligible effect. Other details of outputs are given elsewhere in this Handbook.
Power Supplies.
The power supply circuits are arranged so that either A.C. mains or D.C. supplies can be used,
a change-over being effected by merely plugging in a differently connected snpply socket, and changing
the position of a D.C./A.C. Heater Link in the receiver. The mains on-off switch is not in circuit
when using D.C. supplies. A 2 amps. fuse is used as a link on the primary of the transformer for
selecting the appropriate mains voltage tapping.
When using batteries an economy in H.T. current may be effected by reducing to 160 volts, and
at this value a further economy can be made by replacing the KT.63 by an L.63 if using receiver for
phone reception only. A suitable arrangement of supplies when using batteries and rotary converter
is shown on Drg. WZ.1960, page 45.
The rectifying and smoothing circuits are of conventional design.
In later models a 500 mA fuse is fitted in the earth connection of the high voltage winding of
the transformer, and a spare fuse housed in the lid of receiver.
Controls.
The receiver controls, as shown in Fig. 1, page 2, are :-
1.
On-Off Mains Switch.
2.
Operational Switch (control of A.V.C. and B.F.0.).
3.
Pass-band Switch. (Variable Selectivity).
4.
H.F. Gain Control Potentiometer.
5.
L.F. Gain Control Potentiometer.
6. Band Cban,ge Switch.
7.
Main Tuning Control (coarse and fine controls).
8.
Beat Frequency Oscillator Tuning.
9. Aerial Trimmer Condenser.
Frequency Band.
The overall frequency band, 60 kc/s to 30 Mc/s, with a gap between 420 kc/s and 500 kcis, is
covered by six positions of the Band-change switch. The bands are
1.
60 ke/s to 160 kc/s. 
4. 1.4 Mc/s to 4 Mc/s.
2. 160 kc/s to 420 kc/s. 
5. 4 Mc/s to 11 Mc/s.
3.
500 kc/s to  1.4 Mc/s.

6. 11 Mote to 30 Mc/s.
Timing and Calibration.
The main tuning control has a driving ratio of 25 to 1 and is fitted with a slow motion epicyclic
drive halving a reduction ratio of about 170 to 1. This control, besides opetat:ng the lo2aing scale,
moves a pointer across a scale calibrated directly in frequency. The frequency scale is broujit into
view by the action of the Band-change switch.
Logging Seek. (See Fig. 2, page 4.)
The longing, scale provic'es a method of retuning to a station already locited with rapidity and
accuracy. It has a scale length for each frequency band equi-ialent to 18 feet, and carries 1,250 divisions
large enough to allow accurni; astimation to the nearest quarter of a division. At the highest fiequency
of 30 Mc/s this corresponds to only 5,000 c/S in frequency change, so that readjustment to a given
reading will l-ring a desired C.W. station into sufficiently close adjustment to give a beat note within
the audio band.
( 7 )

Selectivity Control.
The width of the intcrot Late frequency pass-band is controlled by the pass-band switch
having 5 positions. At the 1C3 neles position a low frequency filter tuned to approximately I kc/s
is introduced folich-Ang the 2nd ci.:•.tector.
The pass-band; available ate
6,000 cyc'es total width at half peak amplitude.
3,000 „
tt
ft 1 , 9
1,200 „
5?
300
„
95
!9
100
„ 55
tt 9t
The gain of the intermediate audio frequency stages does not vary more than a few decibels

between any two positions of 
pass-band switch.
I.F. Gain Control.
The gain of the two signal fr:quency stages and the first two I.F. stages is controlled by varying
the positive voltage applied to the cathodes in excess of the normal self-bias developed across the
cathode resistance. The range of control is of the order of 100 db.
Gain ConOtol.
The amplitude of the signal applied to the grid of the first audio frequency valve is varied by a
potfoitiometer of
0.5 M Q, there being a reduction of approximately 50 db when the control is fully
counter-clockwise.
Onittuts.
Three levels of output are available.
(A) Loudspeaker. Approximately 2 watts maximum power.
CR.10014, CR.10015, CR.10017 and CR.100/8 to match 1,000 ohms.
Other models • to match 3 ohms.
On these tatter models the loudspeaker is disconnected when the phone plug
is inserted.
(a) Line. For 60y0 ohms line or amplifier ; 2 mW, unaffected by connecting phones.
(c) Phones. Two phone jacks on front panel. Phones of any convenient impedance,
may be ust..d. Output of the order of 0.3  for high impeoance phones on
standard mo'cls, but considerably higher on CR.100/4, CR. 100/5, CR.l00/7 and
CR.100/8 mo.lels.
Operational Syy ;t eh.
This is a 5-position switch controlling the use of A.V.C. and the B.F.O. The centre position
marked OFF breaks the anode supply to all stages except the L.F. and Output Valves. Its use is to
keep beaters alight diving shoet stand-by periods, thus reducing to a minimum any frequency drift
caused by temperature variations.
The other points of the switch are
•
MOD — VAN ; that is, B.F.O. off, A.V.C. off.
MOD — A.V.C. ; that is, B.F.O. off, A.V.C. on.

C.W. 
A.V.C. ; that is, B.F.O. on, A.V.C. on.
C.W. — MAN ; that is, B.F.O. on, A.V.C. off.
Side-tone Facility.
On the Tyre CR.100/2 receiver facilities are provided for desensitizing the receiver when an
associated transmitter is emitting. This consists in raising the cathode line voitag of the receiver
when the transmitting key is pressed by introdnoirin all or part of a 2,0C10 ohms resistance at the earth
end of the B.F. gain control potentiometer. The resistance is mounted on the top (leek inside the
receiver, and shook'. be adjusted
so
that the operator hears his own transmitted sienal at the desired
amplitude. The connection to we insaLted back contacts of the worse key or relay is made by a
length of shielded twit* cable, teeminnted by a plug. When not in use the side-tone socket on the rear
of the receiver chassis should be shorted, using the special shorting plug provided.
( 8 )

V.
KT.W62
VR100
V.11
U 50
Ntin
V3
X S6
VR9°
I. F.I.
NEW'
CORD
V4
KTV-
1 521
MAIN
TUNING
CONDs_R
Vt3
DH6
Po
V.10
KTW.62
L.F.
FILTER
Cr 10K1
VIS TRAt4 S
FUSE "
VOLTAGE
S ELECTCI,
CONT`
Fig. 3. Plan showing Valve Positions.
Valve Complement.
The valve complement of the receiver is here shown with equivalent types and substitutes. The
valve number refers to that shown on Circuit Diagram WZ.1943, page 47. The substitutes shown in
brackets should be used only in an emergency.
Possible Substitute.
rKTW.61 = NR.64.
(61(70)
( (6J
7 G)
j - X.65 
NR.82.
(6K8G)
I
KTW.61 = NR.64.
(6370)
(_ (6K7G)
1 (6K7G)
L (6J7G)
(6Q7G)
(6F60)
(6V6G)
{
KTW.61 = NR,64.
(6J7G)
(6K7G)
t5Y3G
5Z4G
(U.52)
Valve No.

Type

Use
VI

KTW.62

1st Signal Frequency Amplifier
V2

KTW.62 2nd Signal Frequency Amplifier
Mixer
Frequency-change Oscillator
1st I.F. Amplifier
2nd „  „
3rd „  „
Combined Signal Detector
A.V.C. Diode and L.F. Amplifier
Output Tetrode
Full Wave Rectifier
VR.100
NR.68
NR.85
ARP.17
VR.100
NU.20
V3 
X.66
V4

KTW.62
V5

KTW.62
V6 
KTW.62
V7

KTW.62
V8

DI -
I.63
V9 
KT.63
V10
V11 
U.50
Service Type No.
VR.100
VR.99
VR.100
KTW.62 Beat Frequency Oscillator
For plan of Chassis showing position of valves see Fig. 3.
( 9
)

(B) 1,1riciLoricAL.
The receiver cabinet is of all metal construction (I
r
in. motor body steel) and comprises four
main members ; chassis, cover with hinged lid, front panel and bottom plate.
The chassis is of the inverted type, with riveted and welded corners. It carries on top the high
frequency tuning condenser akid calibration sub-assembly, valves, intermediate frequency transformers,
crystal circuits, L.F.  cutout transformer and parts of the supply circuit. The H.F. coil pack,
condenser and resistance boards and switch controls are carried beneath the chassis.
The front panel is secured to the chassis by Parker Kalon self-tapping screws (which are used
whenever possible el_sewhere on the receiver). To remove front panel, first remove control knobs
and locking ring on supply switch, then take out P.K. screws.
The main cover portion of the cabinet is screwed directly on to the chassis, access to the upper
part of the chassis for valve replacements, etc., being then provided through the hinged lid.
The base is screwed flush on to recessed brackets at the bottom of the chassis, and has holes to
assist ventilation, and domes on which the receiver rests if bench mounted. The bottom plate may
be reversed so that the domes are inwards when the receiver is rack mounted.
The main terminal board and input sockets are mounted at the rear of the chassis, and telephone
jacks at the front.
For servicing, the base and cover portion can be removed, leaving the receiver complete with
front panel intact.
( 10 )

SECTION 4.
PERFORMANCE.
Overall Sensitivity.
The input required to give a signal-to-noise ratio of 20 db (100 to 1 power ratio) on an un-
modulated signal, or a ratio of 10 db (10 to 1 power ratio) on a signal modulated 40 per cent. at
400 cis is shown in Table 1 below, and is measured under the following conditions
A non-inductive resistance of 100 ohms is connected between the signal generator and the
dipole socket or " D " terminal of the receiver, the other dipole terminal being earthed ; the pass-band
switch to 3,000 c/s ; the H.F. gain control at the optimum position ; the A.V.C. not in use. (See page
32.)
TABLE 1.
OVERALL SENSITIVITY.
Band. Frequency.
Aerial Input.
Average.
Receiver.
Maximum
acceptance
figure.
1
60 kc/s 1.5
;IV
2.0
i-tV
155  „
1.2
„
2.0
„
2
155  „ 1.4
„
2.0
„
420  „ 1
.
3
It
2.0 „
3 500
 „ 1.4 „ 2.0
1.4 Mcjs
1.3 „
2.0 „
4
1.4
 „
1 .
6
,,
2.0 „
4.0  „
1
.
2
ft
2.0 „
5 4.0  „ 1.9
,.
4.0
„
11.0  ,.
1
.
4
,,
2.0
„
6 11.0 
„ 3.6
„
5.0
„
28.0 1.7
,,
3.0 „
Autctuat;c Volume Control.
The increase in audio frequency output when the modulated signal input is increased by 60 db
(1,000 to i in voltage) above the input figures given in third column of Table 1 will not exceed 7 db (2.2
to 1 in voltage).
Sze Fig. 4, page 49, A.V.C. Response Curves.
Sele-etivity of Si pa' Frequency Circuits. Image Attenuation.
Table 2 below shows the attenuation offered to the image signal, for frequencies above 1.4 Me/s.
For Al frequencies below 1.4 Mc/s the attenuation is greater than 100 db (100,000 to 1 voltage ratio).

Maximum permitted Bandwidth.
Minimum permitted Bandwidth.
Pgss-band Switch.
TABLE
2.
Average rectiver.
Lowest acceptance figure.
Band.
Frecuelicy.
Voltage
Voltage
db
ratio.
db
ratio.
4
1.4 Mcis
>100 db
>100,0'00 to 1
100 db
100,000 to 1
4  „ 80  „
10,000 to 1 70  „
3,200 to 1
5
4 
,,
94  „
50,000 to 1 84  „
16,000 to I
11  „
60  „
1,000 to 1 50
 ,.
320 to 1
6
11 
,,
59  „
890 to I 50  „
320 to 1
28  „
~
J 30  „
30 to 1
25  ,
18 to 1
Selectitity of Intermediate Frequency Circuits.
The mid-band frequency of the intermediate frequency pass-band is 465-1-2 kc/s according to
the frequency of tile crystal. Table 3 below shows the protection given against adjacent channel
signals for the four conditions of pass-band provided.
TABLE
3.
Pass-band
Switch
Total Bandwidth for attenuation from
Position.
peak as wider.
6 db 40 db 6C db
6,000 c/s
6.0 kc/s
16.0 kc/s
21.0 kc/s
3,000 „
2.7 „
8.5 „ 13.0 „
1,200„
1.2„ 5.4„ 8.8„
300 „
0.35 „
4.5 „ 8.8 „
Table 4 below shows the tolerance permitted in total bandwidth at half peak ordinate, i.e.-6 db.
TABLE
4.
6,000 c/s.
'3,000 „
1,200 „
300 „
8,000 cis.
3,500 „
1,500 „
450 „
5,000 c/s.
2,000 „
1,000 „
250 „
See Fig. 5, page 49, I.F. Response Curves.
Audio Frequency Response.
The audio frequency response is constant to within ±41 db of a mean figure for all frequencies
between 100 and 6,000 c/s. The insertion of the low frequency filter (i.e. the 100 c/s position of the
pass-band switch) ensures that a band of frequencies of approximately 100 c/s in width is passed with
less than 6 db attenuation. Frequencies more than 200 c/s from the mid-band frequency are attenuated
by at least 20 db.
Figs. 6 and 7 show the Audio Frequency Response and L.F. Filter Response curves.
Overall Fidelity Response.
Fig. 8 shows the overall fidelity taken at 1.4
.
111c/s with a modulation depth of 40 per cent. for
four positions of the pass-band switch.
(12)

SECTION 5.
MAINTENANCE AND SERVICING.
Packing and Unpacking.
Do not hold the receiver by its knobs when removing it from its carton.
Turn the main tuning condenser to maximum capacity before transporting the receiver.
See that valves and valve cans are firmly seated, and grid caps connected.
Never lean the receiver on its rear terminals as the aerial sockets arc easily damaged.
Cleaning and Lubricating.
Little attention is required in this respect providing the lid is normally kept closed to exclude
dust. The removal of dust is best done by N
,
acuttra cleaner, or with a medium-size varnish brush,
taking great care not to bend the
v anes of the main tuning condenser. The end vanes of each section
of this condenser are adjusted by the manufacturer to give correct tracking and should not be interfered
with.
Switch mechanism and cord pulley w
heels may require a drop of light machine oil on rare
occasions, but care should be taken not to splash oil on switch wafers. The rotors of switches are lightly
greased when new, and vaseline only should be used for this purpose if ever required, and then used
sparingly. Should the surface of switch wafers become coated with dirt and grease they should be
cleaned with carbon tetrachloride.
General Care.
On models which do not have an external pointer and stop, take care not to force the Band-
change switch past Band 6, thus over-riding the stop and breaking the band-change cord.
If the receiver is out of its case for repair, stand it either in an upright positron, or on its right-
hand side, mains transformer downwards. On no account let the weight of the cnassis rest on the
I.F. Transformer cans.
It is false economy to run with only one dial lamp, as this will then have a reduced life owing
to excess voltage.
Occasionally check up on all knobs to see if grub screws are firmly bedded in their pipping holes.
Checking Valve Performance and Changing Valves.
The H.T. voltage and anode current of valves should be chucked at regular intervals, say, every
thousand hours the receiver is running. If this is not done the grad unl failure of emission in valves is
not noticed until serious reduction in performance is reported. A log of these measurements should
be kept. The H.T. voltage may be measured by connecting a voltmeter between terminal 3 of the
output transformer and the chassis.
When changing valves it may be useful to remember that a tube whose emission has fallen
may be unsuitable for the later amplifier stages or as oscillators, but quite good enough for n further
period of service in the 1st or 2nd Signal Frequency stages where the grid voltage awing is lowtr.
Similarly a slightly noisy valve might be suitable in a later stage but not aceeptale for an early
stage. Certain substitutes indicated in the Valve Complement Tab :e, though useful in an emergency,
cannot be expected to give a performance equal to that specified when using the correct type, end
greater care must be taken in choosing a substitute valve for the oscillator and B.F.O. stages than
elsewhere. An unsuitable type may fail to oscillate, or may generate an os.;:liatory voltage of an
unsuitable amplitude. This is more likely to be so if the receiver is being operated from batteries
where the beater voltage is reduced to 6 volts and the H.T. is lower than 250 volts.
Always measure the H.T. first, and fit a new rectifier valve if the iI.T. has fallen to a value
approaching 200 volts. If this does not restore H.T. to normal, suspect e failing H.T. electrolytic
condenser. The regulation of the rectifier is such that the H.T. voltage rises by about 10 per cent.
when the H.F. gain control is reduced to minimum.
The anode current of the oscillator valve and the mixer vary slightly according to the frequency
and frequency hand in use. The figures given refer to measurements made with the receiver at about
12 Mces on - Band 6.
The use of " preferred %alue,s " and w ide tolerances in resistance values and valve performances
under war-time conditions impose a rather wide tolerance on anode feed figures, and about 20 per
cent. variation in the values given may be regarded as reasonable, except in the case of the rectifier
voltage.
( 13 )

R7 FLAUD HERE N EARL;' MODELS.)
.R i5

_z 1 40
1.7 MA
!
'
7- £0V
'
1.
0 EARTH
.1 R39
-'‘ R7 200V
°SG8.
n
MIXER
H. F
R 17
Fl 4
litnA
250.V. SCREEN t;F1D LINE:00.v
Fig. 9. Plan of Underside showing Test Points.
13
6 tnA _
AERIAL
(0
:CL
L41 I -
0
<
X r-1
La/ L
X 7x
- -
cr <
R46
(1, 4
R 3 0
R 24
0  r
OMITTED
IN SOME
EARLY MODELS
On early models of the receiver the anode current of the valves V3, Y8 and VIO tended to be
somewhat lower than. the flgures given in Table 5, page 15.
A valve feed will fall very low if the screen-grid voltage fails ; e.g., because of a broken-down
&coupling condenser.
A valve feed will rise if the cathode bias resistance becomes short-circuited by a faulty by-pass
condenser.
The feed of the mixer valve will run high if the 1st oscillator output is feeble or fails.
To measure voltage and current, first remove the bottom plate.
Fig. 9, above, shows the position of the various anode and cathode resistances and the values
of current or voltage obtained with maximum 11.F. gain. For convenience, these and other readings
obtained are tabulated opposite (see Table 5). An Avometer or Avominor, or other simple test meter
should be used. In the case of the 1st Oscilintor (V4), measure the D.C. voltage drop across the Anode
resistance, R7 on diagram, As indicated on Fig 9, the position of this resistance has been changed
slightly since the earliest models were introduced. It is easily recognised by its size and colour (red,
3 watt type). On the output valve V9 measure; the D.C. voltage drop across the cathode resistance,
R30 on diagram. On all other valves the approximate anode feed is obtained by connecting the
milliammeter in shunt with the anode decoupling resistance. Care should be taken after clipping
the positive lend of the meter to
 not to let the negative lead touch the chassis or a point of low
D.C. potential, and for this reason the negative lead should have a " probe " connection. It is prefer-
able to use a meter which is fitted with a fuse or automatic cut-out.
( 14)

Volt

aud Current Check. (Sec Fig. 9, page 14.)
Operational Sv,itch to C.W.---MAN. Receiver tuned to about 12 Mc/s Band 6.
TABLE 5.
Test Point
and
Circuit Reference
Meter Reading
I 
Remarks
H.F. Gain at MAX.
H.F. Gain at MIN.
Top of R7 to
chassis
H.T.
250 volts D.C. 280 volts D.C.
Change U50 valve
if H.T. has fallen
by 15%
Junction of R39
and R40 to
chassis
Screen-grid Line 80 volts D.C.
120 volts D.C.
_.
--1-_ 20%
R36 to chassis Cathode Line
0
25 volts D.C.
± 20%
VII Pin 2 to
chassis
Rectifier Output 300 volts D.C.
315 volts D.C.
Tolerance : up to
15% drop.
Across 10
V4, Oscillator 195 volts D.C.
215 volts D.C.
± 10%
Anode Resistance
Across R30
V9, Output Valve 15 volts D.C. 17 volts D.C.
± 20%
Cathode
Across R13 VI, H.F. Amplifier
6.0 mA
0.3 mA approx. ± 20%
Across R14 V2, H.F. Amplifier 6.0 mA 0.3 mA approx.
± 20%
Across R15
V3, Mixer 1.7 mA 1.8 mA
± 20%
Across R16
V.5, I.F. Amplifier 6.0 mA 0.3 mA approx. ± 20%
Across R17
V6,
I.F. Amplifier
6.0 mA
0.3 mA approx.
± 20%
Across R44
V7, I.F. Amplifier 6.0 mA 9.0 mA approx. ± 20%
Across R24
V8, D.D. Triode 1.5 rnA
1.6 mA approx.
± 20%
Across R46 V10, B.F.O. 115 mA 1.6 mA ± 20%
* The three measurements marked by asterisk may be omitted in routine measurements f desired.
(15)

Hints on Tracing Faults.
Whilst it is not
possible to deal with the many and varied faults which may occur in a modern
communication receiver, some help can be given in tracing and curing troubles. But it must
be
pointed out that familiarity with the circuit diagram and the function of each component is the first
prerequisite for successful servicing.
The second necessary qualification is to have a logical method of attack. The
plan recom-
mended
is on the following lines :—
First : Be sure all controls and external connections are correct and that there
are no self-
evident mistakes, such as Operational Switch to OFF, wrong type of phones or phone plug, low
impedance loudspeaker connected to a CR.100/4 or CR.100/5, which models demand a medium
impedance, mains plug or socket not fitting snugly, AC/DC heater link in wrong position or broken,
mains fuse broken or removed, a valve missing or wrongly placed, side-tone shorting plug disconnected
or associated external contacts open. Remove the lids of all valve cans and see that salves are well
seated and grid connections firm. Remove bottom plate of receiver and look for scorched
icn dis-
connected
resistances. Remove B.F.O. cover and inspect for pinched leads. Operate all controls
and listen for unusual effects when switching or varying levels.
Second : Attempt
to locate the stage at which the fault occurs by simple tests and aural
evidence.
Third : If a test meter is available, do not spend too much time on preliminaries, but carry
out voltage and current checks (see Fig. 9 and Table 5) and make use of Table 6 (page 17) and the circuit
diagram to test circuits for resistance and continuity.
Fourth : If the receiver appears to be working but not efficiently, the state
of gang of the
high frequency circuits may be checked by the Detune Test (Table 7, page 33), using
a calibrated output
meter. The H.F. and I.F.
Sensitivity also may be measured, using a calibrated Signal
Generator and
Output Meter (See Table 1, page 11 and page 30).
It should be fairly easy to determine whether a fault is in the early stages,
the intermediate
frequency stages, or at the audio frequency end, by the amount of receiver noise and its nature,
and if
affected by touching or shorting circuits or varying the passband switch and other controls. Complete
absence of noise indicates broken supplies, or discontinuity or valve failure in audio frequency circuits.
A low to medium
level
of noise, which may or may not vary in pitch as the Passband Switch is varied,
will generally point to a fault in
the I.F. Circuits
or Frequency Changer.
A high level of receiver noise with a distinct change in its pitch and intensity as the Passband
Switch is varied but failure to receive signals will generally indicate a fault in Signal
Frequency or
Oscillator Circuits.
There
remain a number of faults not so readily classified, some easily found and others more
obscure. Some detailed hints are given under the following headings :—
(A) Audio frequency circuit faults.
(a) Intermediate frequency circuit faults.
(c) Signal and Oscillator frequency and Mixer faults.
(D) Miscellaneous electrical faults.
(n) 
mechanical faults.
( 16 )