Eddystone model 750 Instruction manual VK7AG
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COMMUNICATIONS RECEIVER.
Model “750”
Instruction Manual
The Eddystone ‘750’ receiver is of the double superhetrodyne type and combines high
sensitivity with an unusually good signal-to-noise ratio. All but two of the eleven valves
are of the miniature type, details being provided with the circuit diagram. The selectivity
is continuously variable over wide limits and this feature, in conjunction with the separate
RF, IF and AF gain controls, enables maximum results to be secured under varying conditions
of operation.
The four ranges are as follows :
Band |... 32 Mc/s, to 12 Mc/s.
Band2... 12 Mc/s. to 4:5 Mc/s.
Band3... 4:5 Mc/s.to 1:7 Mc/s.
Band4 ... 1465 Kc/s. to 480 Ke/s.
The fifth position of the wavechange switch desensitises the RF section of the receiver to
permit a pick-up to be used without break-through.
The Amateur Bands are distinctively marked in green, on the basis of the International
allocations made at the Atlantic City Conference in 1947. The broadcast bands are shown in
red. It should be noted that the scale markings (all in frequency) are linear and also that the
International Distress frequencyof 500 Kc/s. is covered.
Hele Uae pe A, ee
INSTALLATION and OPERATION
of the inte
control at
cutting the
The receiver has been carefully aligned and calibrated, and thoroughly tested before despatch. Because of
The only adjustment that may be necessary is the mains input voltage. The plug in the carrier. |
selector panel on the transformer is fitted normally in the 230 volt position, where it should . creasing as
remain for voltages between 220 and 250 volts. If the mains voltag e 195 and 215
is between distortion
volts, the plug should be changed to the 200 volt position. The 10 volt tap is suitable for is a valuab
mains supplies between 100 and 125 volts. tuning and
D.C. mains supplies are entirely unsuitable and if connected will cause serious damage.
Ensure that the octal plug is in place in the octal socket ‘‘ B.’ (nearest the side of the Switching
cabinet) as shown in the drawing, Fig. 2. a valve (V9)
A loudspeaker of 2:5 to 3 ohms impedance should be connected to the two upper terminals The adjust
at the rear (the Eddystone Cat. No. 688 is especially recommended for use with this receiver), incoming
or alternatively high resistance (2,000 to 4,000 ohms) telephones plugged into the jack at the latter is pc
left of the front panel. - RF gain ca
The fuse fitted between the H.T. secondary centre tap and chassis is a ‘' Magnickel '’ delayed A certain
type.A standard type of fuse is liable to blow if the receiver is switched off (mains switch) When rec
and immediately switched on again without giving the rectifier valve time to cool. of the sign
AERIAL CONNECTIONS. The IF gai
when sele
Ifa single long wire is used or any aerial with a single wire type of feeder, connection is made selectivity
to the rear terminal marked ‘‘A,”’ the other terminal marked ‘‘ AE '’ remaining strapped ment of tl
to the chassis. A good earth connected by a short lead to the second terminal will
improve results, particularly on the lower frequencies, but if there is any doubt about the It is advan
efficiency of the earth, it may be better to leave it off. receiver i:
the noise |
For optimum performance, both as regards bringing in weak signals and for keeping noise control at
down to a minimum, an aerial cut to resonate over the frequency band in which the user is made to :
mainly interested is strongly recommended. The lengths for dipole aerials to give optimum tuning cor
results at certain frequencies are tabulated below. For details of other types of aerials and
feeder systems, the reader is advised to consult the various Handbooks which deal with Another ¢
these specialised subjects. each side «
Broadcast Amateur note of I,
Wavelength (Metres) .. 49 31 25 19 (6 13 II 40 20 10 signal to |
Frequency (Megacycles).. 61 96 II-B [5-1 17:8 21-5 26 7 |4 28 the knob
Length of each arm (feet) 40 26 20 155. 13 105 9 33. «16-5 8-25
The mech
RECEPTION OF TELEPHONY.
The verni
With the BFO switch in the “‘ off’’ position, the automatic gain control circuits become scale is gr
operative and for full effectiveness, both RF and IF gain controls should be set at maximum the main
(full clockwise rotation) and the volume controlled with the audio gain potentiometer on the divisions :
extreme right. On very strong signals, particularly with a large aerial and on medium waves,
The actuz
it is possible for overloading to occur and it then becomes necessary to reduce the RF gain.
of each ir
To begin with, the variable selectivity control should be to the extreme right, giving mini-
mum selectivity. In this position, reasonably good quality of speech and music will be
obtained but, as the selectivity is still considerably higher than that of an average receiver,
a certain amount of side-band cutting occurs and high fidelity reproduction is not to be
expected. A minor point to be noted is that the loudspeaker or telephones should be
capable of responding to low audio frequencies (down to 100 or 150 cycles), otherwise the
middle audio register is likely to be unduly emphasised.
When heterodyne interference is experienced, the selectivity should be increased by
rotating the control to the left, thereby reducing the bandwidth and weakening the strength
aN
ION of the interfering whistle. It is not advisable to operate on telephony with the selectivity
control at maximum (except perhaps on a very crowded amateur band) because sideband
cutting then becomes severe and speech quality deteriorates in consequence.
e despatch. Because of the high selectivity, it is important to tune carefully to the centre of the received
alug in the carrier. It should be remembered also that the AGC action results in the sensitivity in-
re it should creasing as the receiver is tuned slowly away from the centre of the carrier, giving rise to
(95 and 215 distortion and apparently reducing the actual selectivity. The Cat. No. 669 ‘S"’ Meter
suitable for is a valuable adjunct when the main interest lies in telephony reception since it aids correct
tuning and also gives a comparative idea of the strength of the received carrier.
us damage. RECEPTION OF CW SIGNALS.
side of the Switching on the BFO (also thereby cutting out AGC) applies H.T. to the beat oscillator
valve (V9) and reception of CW Morse signals is then possible.
ir terminals The adjustment of the controls depends on a number of factors including the strength of
s receiver), incoming signals, amount of interference present and the efficiency of the aerial. If the
: jack at the latter is poor, it will be advisable to use maximum RF gain atgll times but, if good, often the’
RF gain can be reduced somewhat with advantage, particularly on strong signals.
1 ’’ delayed A certain amount of skill will be called for in adjusting the IF gain and selectivity controls.
ains switch) When receiving telephony, the IF gain is automatically controlled according to the strength
ol. of the signal but, with CW, manual control of IF is important.
The IF gain varies to some extent with the setting of the selectivity control and is greatest
sion is made when selectivity is minimum. It will rarely be desirable to employ full IF gain with minimum
ng strapped selectivity. As the degree of selectivity is increased, gain should be maintained by advance-
rminal will ment of the IF gain control.
t about the It is advantageous to employ a high degree of selectivity because the noise output from the
receiver is partly dependent on the IF bandwidth and the narrower this is made, the less
eping noise the noise for the same amount of gain. When the receiver is operated with the selectivity
| the user is control at maximum, signals very close to one another can be separated and weak signals
ve optimum made to stand out clearly against the extraordinarily quiet background. Naturally the
Faerials and tuning control must be handled gently under such conditions.
h deal with Another control which calls for attention is the BFO pitch. This gives a swing of 3 Ke/s.
each side of the centre point (white spot at the top). Normally it will be set to give a beat
vateur note of 1,000 cycles (or near) but careful handling of this control will often enable a desired
20 ~=«10 signal to be separated from an interfering one. Also, it is sometimes of benefit to rotate
14 28 the knob from one side of zero beat to the other when interference comes up on a signal.
6:5 8-25 BANDSPREAD.
The mechanical bandspread device is available over the whole range covered by the receiver.
jits become The vernier logging scale gives an effective length per range of approximately 32 feet. This
it maximum scale is graduated from 0 to 100 divisions and is read in conjunction with the lowest scale on
leter on the the main dial, the latter being marked off with 25 major divisions, each representing 100
Jium waves, divisions of the vernier scale (i.e., one complete revolution).
the RF gain. The actual amount of bandspread on the amateur bands depends of course on the width
giving mini- of each individual band. The following details apply :
usic will be Vernier Scale Number of Vernier
ge receiver, Band (Mc/s.) Length (inches) Divisions
s not to be 29-7 —28 34-375 208
s should be 21-45 —21 75 4555
herwise the 14-35 — 14 6-45 39
73 -—7 15 91
icreased by 40 — 35 él 364
he strength 20 — 18 30 182
a
NOISE LIMITER.
In a quiet situation, it will not be necessary to make use of the noise limiter but when
electrical interference of a staccato nature is experienced (on telephony or CW), switching
on the noise limiter will effectively remove a high percentage of the interfering noise, with
little effect on the strength of the signal and without introducing distortion. The noise
limiter must not be expected to act effectively with noise of a mushy type, as generated by
vacuum cleaners and other electrical equipment incorporating motors — these should be
filtered with suppressors at the source.
In a noisy location, it is well to erect an aerial well in the clear and as far as possible from
electric light wiring. The stronger the incoming signal, the more the gain of the receiver
can be reduced (automatically on telephony, manually on CW) thereby reducing also the
effect of any interference being picked up.
USE OF THE STANDBY SWITCH.
The Standby switch, in the ‘‘ off’’ position, desensitises the receiver very considerably.
This system is considered preférable to cutting the H.T. supply, for several reasons. The
oscillator valves continue to operate under normal conditions, thereby preventing any
change of frequency during standby periods and, since the audio stages remain “‘ alive,’’,a
monitor signal can be fed into the pick-up terminals and become audible on the loudspeakef,
or telephones. ji
The receiver itself also becomes available as a monitor of the outgoing signal. It is necessary
to prevent excessive RF voltage reaching the receiver aerial terminals during transmission
and the wires to these terminals should be kept as short as possible. If a separate aerial is
CC
used for reception, arrangements should be made for disconnecting or earthing it during
periods of transmission.
CONNECTION OF “S” METER.
The Eddystone Cat. No. 669 ‘‘S ”’ Meter is recommended for use with the ‘* 750 ”’ Receiver.
It incorporates a sensitive moving-coil meter of 200 microamperes full scale deflection.
The flexible lead from the meter terminates in an octal plug which should be inserted in the
sockét marked ‘‘ A '’ in Fig. 2 at the rear of the receiver.
Reference to the circuit diagram of the receiver will show that one half of the double-diode
V7 is in series with the meter movement. This prevents reverse current flowing through the
meter when the balance is disturbed and the meter can be left in circuit under all conditions The Ed
of operation without likelihood of damage. The bottom bend characteristic of the diode sensiti)
results in sluggish action at low signal strengths and, to overcome this, the needle of the are of 1
meter is purposely offset below the zero mark on the scale by means of the mechanical is cont
adjuster. RF, IFz
With the receiver controls set for reception of telephony, the aerial and earth terminals (or of opel
doublet terminals) should be shorted and the ‘‘ S ’’ Meter needle made to coincide with zero
The fo
by adjustment of the electrical balance control at the rear of the meter. On removing the
short, the meter will indicate comparative carrier strength.
OPERATION FROM 6 VOLT ACCUMULATOR.
The ‘' 750’ receiver may be operated from a 6 volt accumulator in conjunction with a
special Vibrator Power Unit, Cat. No. 687/|, which is fitted with leads and plugs ready for The fit
immediate use. Installation details are provided with the Power Unit.
permit
The A
allocat
STRATTON & Co., Ltd., West Heath, Birmingham, 31 red. |
Intern
Cables : “STRATNOID” Birmingham Telephone : PRlory 2231-2-3-4
Aa
Printed in England
EDDYSTONNE
E ‘750’
ALIGNMENT INSTRUCTIONS
lt is assumed that test instruments are available— in particular, a ceramic tracker condenser shown in Fig. 3 has been very carefully
Signal Generator covering 85 Kc/s. to 32 Mc/s. and provided with adjusted for proper tracking on Range 4 and it is not advisable to
internal modulation (30%, ) and a calibrated attenuator ; and an audio touch it.
output meter, calibrated in milliwatts and decibels and adjustable Range |. 13 Mc/s. and = 31 Me/s,
to match an impedance of 25 ohms. Trimming should be carried Range 2. 5 Mc/s. and II Me/s.
out with a non-metallic tool such as the Eddystone Cat. No. 122T.
Range 3. 2Ric/s. and = 4 Me/s.
IF STAGES, Range 4. 500 Kc/s. and 1400 Kc/s.
The controls should be set as fallows : To proceed with the alignment of the RFand Mixer stages, the BFO
RF Gain minimum Band Selector Range |. is switched off, the crystal oscillator removed and the modulated
output from the Signal Generator connected to the aerial and earth
IF Gain maximum - BFO Off. terminals, via the dummy aerial. The attenuator is set to give an
AF Gain maximum Noise Limiter Off. output of between 10 and 20 microvolts.
Selectivity maximum. A signal on 13 Mc/s. should be injected and tuned in on Range | of
A 30%, modulated input, at 85 Kc/s., is applied between chassis and the receiver, The CORES in the RF and Mixer stages are then
the grid of V4* (the second frequency changer), and the four cores in adjusted for maximum output as indicated by the output meter.
the IF transformers marked '‘ 2nd ”’ and ‘' 3rd” in Figs | adjusted Next, the S.G. is set to 30 Mc/s. and the output peaked by adjustment
to give maximum output, as indicated on the output meter. The of the TRIMMER CONDENSERS. Adjustment is again made at 13
attenuator of the S.G. should be adjusted as necessary to prevent the Mc/s. and the procedure repeated until no further improvement is
needle of the output meter going off the scale. An input of about 280 possible.
microvolts will normally be required to give 50 milliwatts at the The other ranges are aligned in the same way, using the following
speaker terminals. high and low frequency alignment points on each range :
Trimmer Core RF Mixer
“Range Frequency Frequency Coil Coil
| 30 Me/s. 13. Me/s. I 2
2 Il Mejs. 4-7 Mc/s. 4 5
3 4:2 Mc/s. 2 Me/s. z: 8
4 1350 Ke/s. 550 Ke/s. 10 18 W
2
TPUT_TRANSFORM
FUSE. MAINS
LOUD SPEAKER TERMINALS,
LOUDSPEAKER TERMINALS. AERIAL TERMINALS.
tEABS
Fig. 1 8
Leaving the controls and connections undisturbed, the input
eed to. 1620-Kels, and the-sccond oscillator
adjusted, by moving the core In the V4 screening can (see Fig. 3),
until output is maximum. Because of the slight loss in conversion, a
greater input (by some 2 or 3 db) will be required to give 50 milli-
watts output. The change to 85 Kc/s. can be obtained with the
oscillator on either the high or the low side of 1620 Kc/s, and two
Positions of oscillator core will give output — the lower frequency
position, with the core furthest in, is the correct one. 8
The band selector switch should now be moved to ‘'G ”’ and the
1620 Ke/s. input applied between chassis and the stator of the centre PICK -UP TERMINALS. if
section of the gang condenser. The primary and secondary cores in SERIAL No. PLATE. TAL
the first IF transformer (see Fig. 1) are then adjusted to give «« EXTERNAL LT.
maximum output and a further very slight and very careful adjust- QCTAL SOCKET A
ment of the V4 oscillator core may give an improvement. The final TI
“S*METER.
IF sensitivity should be such that 50 milliwatts output is produced
for an input (at 1620 Kc/s.) of between 5 and 10 microvolts. Fig. 2
BFO ADJUSTMENT. VOLTAGE VALUES.
With the BFO switch at “‘ off,’’ a modulated signal should be applied The voltages are between the point indicated and the chassis. Set
and tuned in accurately on the receiver. The modulation is switched the receiver at 28 Mc/s. on Range | with the aerial shorted out, IF
off, the BFO switched on and, with the pitch control at half-mesh and RF controls set at maximum. AF gain control set at minimum
{white spot at top), the core in the BFO unit (see Fig. 3) is set to give with BFO on. Two sets of values are given using different meters as
zero beat, shown. It will be evident that the actual voltage indicated depends
on the meter employed. A tolerance of plus or minus 5%, should be
-allowed on the values given.
Circuit Weston Avo
Reference —_ 1,000 ohms/Volt Model 40
A * 225 volts 225 volts
B 8 CY 90 3
Cc lo, 95
D gC, 80 ‘
E 235. x 236 ¥
F 16, Ss,
G “98 73 »
H wm 75 .
J 232 x 230 #
i) madOOO lL
K
85
la,
a 80
FSB og
‘i
Fig. 3 . M 235 st 235 5
. N 85 < 80 =
RF ALIGNMENT. P 09, 09K
The controls remain as before but with the RF gain also turned to Q 65 a 13 *
maximum. Should it be found necessary to correct discrepancies in R 10. O7. =.
the scale calibration, the output froma Crystal Frequency Standard Ss 235 = 235 Zs
IF STAGES. Range 4. 500 Ke/s. and 1400 Ke/s.
The controls should be set as follows : To proceed with the alignment of the RF and Mixer stages, the BFO
RF Gain minimum Band Selector Range |. is switched off, the crystal oscillator removed and the modulated
output from the Signal Generator connected to the aerial and earth
IF Gain maximum - BFO Off. terminals, via the dummy aerial. The attenuator is set to give an
AF Gain maximum Noise Limiter Off, output of between 10 and 20 microvolts.
Selectivity maximum. A signal on 13 Mc/s. should be injected and tuned in on Range | of
A 30% modulated input, at 85 Ke/s., is applied between chassis and the receiver. The CORES in the RF and Mixer stages are then
the grid of V4* (the second frequency changer), and the four cores in adjusted for maximum output as indicated by the output meter.
the IF transformers marked ‘‘ 2nd "’ and “3rd” in Figs | adjusted Next, the S.G. is set to 30 Mc/s. and the output peaked by adjustment
to give maximum output, as indicated qn the output meter. The of the TRIMMER CONDENSERS. Adjustment is again made at 13
attenuator of the S.G. should be adjusted as necessary to prevent the Mc/s. and the procedure repeated until no further improvement is
needle of the output meter going off the scale. An input of about 280 possible.
microvolts will normally be required to give 50 milliwatts at the The other ranges are aligned in the same way, using the following
speaker terminals, high and low frequency alignment points on each range :
Trimmer Core RF Mixer
“Range Frequency Frequency Coil Coil
I 30 Mc/s. 13. Mcjs. | 2
2 Il Me/s. 4:7 Mc/s. 4 5
3 4-2 Mc/s. 2 Me/s. 7 8
4 1350 Ke/s. 550 Ke/s. io | ou
i
LOUD SPEAKER TERMINALS. AERIAL TERMINALS.
Fig. 1 (ey
Leaving the controls and connections undisturbed, the i
should-be-changed tc. 1620 Ke/s. and the second o: jf
adjusted, by moving the core in the V4 screening can (see Fig. 3),
until output is maximum. Because of the slight loss in conversion, a
greater input er some 2 or 3 db) will be required to give 50 milli-
watts output. The change to 85 Kc/s. can be obtained with the
oscillator on either the high or the low side of 1620 Kc/s. and two
Positions of oscillator core will give output — the lower frequency
Position, with the core furthest in, is the correct one.
The band selector switch should now be moved to ‘'G’’ and the
1620 Ke/s. input applied between chassis and the stator of the centre PICK -UP TERMINALS. ms \
section of the gang condenser. The primary and secondary cores in SERN PLATE, OCTAL pLuG"B”
the first IF transformer (see Fig. I) are then adjusted to give Oct sy EXTERNAL LI.
maximum output and a further very slight and very careful adjust- QCTAL SOCKET A”
ment of the V4 oscillator core may give an improvement. The final eee
IF sensitivity should be such that 50 milliwatts output is produced
for an input (at 1620 Ke/s.) of between 5 and 10 microvolts, Fig. 2
BFO ADJUSTMENT. VOLTAGE VALUES.
With the BFO switch at ‘‘ off,’’ a modulated signal should be applied The voltages are between the point indicated and the chassis. Set
and tuned in accurately on the receiver. The modulation is switched the receiver at 28 Mc/s. on Range | with the aerial shorted out, IF
off, the BFO switched on and, with the pitch control at half-mesh and RF controls set at maximum. AF gain control set at minimum
(white spot at top), the core in the BFO unit (see Fig. 3) is set to give with BFO on. Two sets of values are given using different meters as
zero beat. shown, It will be evident that the actual voltage indicated depends
on the meter employed. A tolerance of plus or minus 5%, should be
RANGE 4 TRACKER. -allowed on the values given.
G00 7 OF ve Circuit Weston Avo
A = Reference 1,000 ohms/Volt Model 40
BFO, TRIMMING. aeney T A * 225 volts 225 volts
me a0 B 98 é 90 is
coy |PERE or ‘TRIMMING. c 10 | 95
D 82 ‘a 80 es
E 235 a 236 *
) @PEPLOEP-Lwer F 16, V5.
cea Pac G "98 i 73 FA
H 78 i 75 a
@wiDtoe-j we! , J 232 as 230 a
mar OOO ~ K
L 85
lf ,,
‘ 80
D2
»
Fig. 3 M 235 i 235 eS
KN 85 “ 80 .
RF ALIGNMENT. P 09) O93 5
The controls remain as before but with the RF gain also turned to Q 6 13 ”
maximum, Should it be found necessary to correct discrepancies in R 10 OF) os
the scale calibration, the output from a Crystal Frequency Standard S 235 es 235 an
should be applied to the aerial terminals (the calibration of most Signal T 227 = 225 3
Generators is not accurate enough). Adjustment is then made to the U 42 i el
cores and trimmers appropriate to each range, in the oscillator Vv 150 i 150 3
section of the coil box (see Fig, 3). Checks and adjustments should w 235 i 235 ”
be made at the frequencies given below, using the TRIMMER x 275 on 272 «
CONDENSER at the higher frequency end ofthe scale and the We a5 70 ‘f
CORE at the lower frequency end. The BFO should be switched on Be 220 5 0-9
for these tests, with the pitch control at ‘‘12 o’clock.’’ The A— 250 * AS 250 a AEs
B— 250 sn AS 250 ay ALC,
*Accessible under the chassis.(see Fig. 3). H.T. Consumption : 96 mA.
r ————
|
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* PIN CONNECTIONS.
VALVE|V. Nola ]2[3]4[5[6[7[6| SERIES.
» ° 1163] H |H] A |G2| K | -
6BA6 |wis9.| |S B7G.
2 7 Gi] ]H [HA |G3{ca] -
> 8D3 | v3. S B7G.
H [AHAT ici] K[H
OCT eee ECH49! v2.4. ba BBA.
a 5Z4G| vio. |= |H|~ [Aa lai] - kK | OCTAL.
7 Wwri50b0_ vi. [-{k|-|-|a]-|-|-| OCTAL.
* bi D77_|_vz_|kiloa|H }H{K2|s |pi|-|_ B7G.
{DH77| vo. [oi k|H|H|o1o2|a|-| B7G.
B7G SERIES. 5 G1] K|H |H] Aj — |G2j—
N78 | ve | i B7G.
i
hie R21 470,000 ohms. Type I6. R42 150 ohms. c7 10-386 pF. (RF Sect. Gang Cond.) er Moulded Mica. Silvered Mica.
33,000 ohms. IW. R22 470,000 ohms. Type 16. R43 47,000 ohms. ca Silvered Mica. Moulded Mica. + 2% Silvered Mica.
Re 1,000 ohms. Type 16. R23 15,000 ohms. IW. R44 47,000 ohms. Jub. Paper. Silvered Mica. Tub. Paper.
R3 10,000 ohms. ‘W. R24 330 ohms. 4W. R45 1,000 ohms. ‘Tub. Paper. + 2% Silvered Mica. + 2% Silvered Mica.
R4 1,000 ohms. Type 16. R25 100,000 ohms. Type 16. R46 2,000,000 ohms, ‘ub. Paper. Ceramic Trimmer £ 2° Silvered Mica.
RS 10,000 ohms. Type 16. R26 470,000 ohms. Type 16. R47 100, ohms. Jub. Paper. negative temp. Tub. Paper.
R6 IZ ohms. 3W. R27 22,000 ohms. Type 16. R48 2,700 ohms, livered Mica, . coefficient. Tub. Paper.
R7 27,000 ohms. |W. R28 10,000 ohms. Type 16. R49 —- 100,000 ohms. Silvered Mica. 1% Silvered Mica. Tub. Paper.
RB 1,000 ohms. Type 16. R29 220 ohms. 4W. R5O 6,800 ohms. Air Trimmer, Air Trimmer. 2% Silvered Mica.
9 1,000 ohms. Type 16. R30 47,000 ohms. Type 16. RSI 27,000 ohms. Sjlvered Mica, -+ 1% Silvered Mica. 2% Silvered Mica,
RIO 10,000 ohms. Type 16. R31 1,000,000 ohms. Type 16, RS2 3,900 ohms. Type 6 or TypeT. lir Trimmer. Air Trimmer. Tub. Paper.
Ril 33,000 ohms, IW. R32 470,000 ohms. Type 16. R53 12 ohms. Type T. Silvered Mica. -£ 1% Silvered Mica, £ 2% Silvered Mica,
RI2 27,000 ohms. Type 16. R33 470,000 ohms. Type 16. R54 1,400 ohms, sw. ‘ir Trimmer. Silvered Mica. = 2% Silvered Mica.
R13 270,000 ohms. Type 16. R34 100,000 ohms. Type 16. Air Trimmer. Air Trimmer. + Silvered Mica.
RI4 AT ohms. 4W. R35 68 ohms. Type | CONDENSERS, (Mixer Sect. Gang Ceramic Trimmer Silvered Mica.
RIS 1,000 ohms, 3W. R36 100,000 ohms. Type 16. cl 3-23 pF. Air Trimmer. | Cond.) (Osc. Sect. Gang Tub. Elect. 350v,
RI6 33,000 ohms. $W, R37 500,000 ohms, Potentiometer. C2 20 pF. Silvered Mica. Silvered Mica. Cond.) D.C. wkg.
R17. 470,000 ohms. Type [6. R33. 3,000 ohms, Type I6, C3 3-23 pF. Air Trimmer. Tub. Paper. Tub. Paper. Moulded Mica.
RIS 68 ohms. Type 16. R39 = 470,000 ohms. Type 16. C4 6 pF. Silvered Mica, Tub. Paper. Tub. Paper Moulded Mica.
RI9 10,000 ohms. Potentiometer. R40 51,000 ohms, 3W. cs 3-23 pF. Air Trimmer. ‘Jub. Paper. Tub. Pap-.. Moulded Mica. -O1 mfd.
R20 470,000 ohms. Type 16. R4l 10,000 chms. Potentiometer. C6 3-23 pF. Air Trimmer, Silvered Mica. Silvers s Mica. Silvered Mica. “Ol mfd,
=
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PIN CONNECTIONS.
i fees
\LVE|V. Noli [27 3]4[5[6]7]6| SERIES.
tical H [HA [G2] kK] -
3A6 |ws9.| |S
17
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D3 | v3. Ss
H [AHATGaG2iGi| KH
[H42| v2.4. G4
4G | vio. |- |H|~ 1A ~ |At|-|K | OCTAL.
50nd vit. [-[K|-|-[al-|-[-[ OCTAL.
)77_|_v7_|kt}D2] H }H [Kal $ [Dil -
H77 | V6. [Gi] K]H|H|D1/02/ A |-
Gi] K}H |H| A] — |G2)—
78 | ve. is3|
EDDYSTONE 750’ COMPONENT VALUES ii
21 470,000 ohms. Type 16. (RF Sect. Gang Cond.) or Moulded Mica. Pues Mica. Moulded Mica.
22 470,000 chms. Type 16. Tye
ype 16 16. Silvered Mica. Moulded Mica. + 29 Sllvered Mica. Tub. Paper.
23 15,000 ohms. IW. Type 16: ‘Jub. Paper. Silvered Mica. Tub. Paper.
24 330 ohms. 4W. 4W. Tub. Paper. “2% Silvered Mica. + 2% Silvered Mica. Tub. Paper.
25 100,000 ohms. Type I6. Type 16. Tub. Paper. Ceramic Trimmer #, 2 Silvered Mica. ilvered Mica.
26 470,000 ohms. Type I6. Type 16. b. Paper. negative temp, ilvered M
27 22,000 ohms, Type 16. if 5% Ww. Ivered Mica. . coefficient. Elect. I5v. D.C. wkg.
28 10,000 ohms. Type 16. ype
BA Sllvered Mica. zi I % eUvered Mica, aper, Tub. erepees
29 220 ohms. 3W. Air Trimmer. ilvered Mica. }- 2% Silvered Mica.
30 47,000 ohms. Type |6. Ivered Mica. a "\94 Silvered Mica. Silvered Mica. Pitch Condenser.
31 1,000,000 ohms. Type 16. Type 16 or TypeT. ‘ir Trimmer, Air Trimet: aper. Silvered Mica.
32 470,000 chms. Type 6. ype T. pF. Silvered Mica. <b 1% Silvered Mica, ered Mica. Tub. Paper.
33 470,000 ohms. Type 16. R54 ‘1,400 ohms, 3-23 pF. Air Trimmer. ered Mica. Tub. Paper.
34 100,000 ohms. Type I6. 3.23 pF. Air Trimmer, Air Trimmer. + Silvered Mica. Tub. Paper.
35 68 ohms, Type 16. CONDENSERS. 10-386 pF. (Mixer Sect. Gang 15-45 pF. Ceramic Trimmer Silvered Mica. Tub. Paper.
36 100,000 ohms. Type I6. cl 3.23 pF. Air Trimmer, Cond.) 10-386 pF. (Ose. Sect. Gang ne ae 350v. Moulded Mica.
37 500,000 ohms. Potentiometer. C2 20 pF. Silvered Mica. 100 pF. Silvered Mica. Cond.) Elect, 450v. D.C. wkg.
38 3,000 ohms. Type I6. ¢3 3-23 pF. Air Trimmer. -O1 mfd. Tub. Paper. “Ol mfd. Tub. Paper. Maulded Sica. Elect, I5v. D.C. wkg.
39 470,000 ohms. Type 16. C4 6 pF, Silvered Mica, “| mfd. b. Paper. -O1 mid. Tub, Paper Moulded Mica. Elect. 450v. D.C. wkg.
40 51,000 ohms. 4W. cs 3-23 pF. Air Trimmer. 1 mfd. ‘Tub. Paper. “Ol mfd. Tub. Pape. Moulded Mica. Tub. Paper.
41 10,000 ohms. Potentiometer. C6 3-23 pF. Air Trimmer. 10 pF. vered Mica, 100 pF. Silvers. Mica. Silvered Mica. Tub. Paper.
EDDYSTOYS "750" RECEIVER.
ie primar, winding of Range 4 osoillator coil (No. 12 ocil)
is now deleted. The wire from the switch wafer to this winding is now
taken to the Lower end of the remaining winding which joins 037 & C39.
The tracking condenser C37 (situated below C39) nwo consists
of two parallel gapacitors, one a 50p¥ silver wica and the other a 40pf
mexamkx N. 1. 6. ceramicg
The follewinz compomwents are chanzed or added:-
C26, G29 ani C30 changed to Ceramic type (negative temp. ocefficient)
C87, / *12pF Ceramic (N.T.¢.) place; in parallels with C40
R55 / 100,000 ohms 3 watt. placed in between HT line and
junetion of R13 and RLY.
TSV/IMW/PBL/ 237» K IDper