Australian Post Office
Telephone Engineering Instructions
Issue 1, April 1948
MAGNETO HANDSET TELEPHONE FTR-804A - SERIAL 1, ITEM 138
MANUFACTURED BY FEDERAL TELEPHONE AND RADIO CORP. U.S.A.
1.1 A limited quantity of the above mentioned instruments has been
purchase by this Department to provide relief in magneto areas during & period
of acute shortage of telephones.
2. GENERAL DESCRIPTION
2.1 The complete instrument is housed in a die-cast case. A view with the base plate from the metal case
and showing the layout of the component parts are shown below. A notable feature of the design. is that the cradle assembly and
the electrical springset are attached to the case.
The telephone TTR-804-A will be issued with a 5 conductor line cord and a terminal block. The design of the telephone provides
for conversion Crow a table instrument to a well instrument by reversing the cradle assembly on the case. fl is not intended to
make use of this facility and the telephones eve to be issued and used for service as table instruments only.
3. CIRCUIT DIAGRAMS
3.1 A circuit diagram is supplied by the manufacturer and pasted inside the case. A diagram using the
Department’s standard symbols And method of presentation is shown on Drawing C.E. 475 which is reproduced below.
Arrangements are being made for a suitable diagram to be made available for replacement purposes.
4. EXTERNAL CONNECTIONS
4.1 Connections to line and battery are block supplied with the instrument.
4.2 Standard battery equipment using two 1.5 dry cells should be employed.
5. COMPONENT PARTS AND SERVICE ADJUSTMENTS.
5.1 The built-in bend generator is capable of delivering 85 mA into a non-inductive load of 200 ohms at 200 rpm crank speed (1000
rpm armature speed).
5.2 The magneto bell coils have a total D.C. resistance of 2000 ohms, each winding consisting of 11,050 turns. The minimum operating
current is 20 mA. A biasing spring is provided on the bell movement but no use of this facility is intended. The biasing spring should be placed in the
left hand notch. (looking at the bell movement from the armature end) in which position
“no-bias” condition should be obtained. To check the adjustment move armature against either pole piece where it should remain firmly in position in both cases. The clearance between residuals and pole piece should be between 20 and 30
mils. The armature end play between bearings shall not be less than two mils and not more than 30 mils. The adjustment of the gongs is effected in the same manner as for the standard bell type 59U.
5.3 No condenser is provided in series with the bell coils but adequate mounting space is available on the base plate between the generator and the bell mounting plate to enable a condenser to be fitted if necessary. The connections to the terminal strip are arranged so that a condenser can be included in the circuit without disturbing the main wiring form. However, initially, in order that the instruments shall be placed into service with a minimum of delay, it is essential that their use should be restricted to areas where circuit arrangements are not affected by the permanent D.C. loop on the line. When the supply position eases provision of a condenser in series with the bell may be made as the opportunity offers. In this connection, condenser No. 27, 1.7uF + 0.4uF, Serial 25, Item 32B, should be used. The 1.7uF unit is to be placed in series with the bell coils and the 0.4uF unit in the
anti-sidetone circuit as indicated in dotted lines on Drawing C.E. 475. The connection of the 0.4uF condenser should be restricted to services with extreme line capacity but, under normal line conditions, this condenser should not be connected in the circuit.
5.4 The Induction coil has a closed core with butt joints and is equipped with three inductive windings as follows:-
| Winding 1
|| 2 ohms
| Winding 2
|| 18 ohms
|| 200 ohms
5.5 The anti-sidetone circuit of the instrument makes use of a non inductive resistance on which various tappings are provided. The telephones as delivered by the manufacturer have the wiring connected to Tap 3 which corresponds to a range of line loop resistance from 300 to 750 ohms. Should the line loop resistance be outside this range the tapping has to be changed as follows:-
||Range of Line Loop Resistance (ohms)
|| 50 - 200
|| 200 - 300
|| 300 - 750
|| 750 - 1200
|| 1200 - 1800
|| 1800 - 2100
It is essential that the lowest resistance tapping that provides satisfactory sidetone suppression should be used in order to obtain maximum receiving efficiency of the instrument.
5.6 The moulded plastic handset is fitted with capsule type transmitter end receiver insets.
6. PARTY LINE SERVICES
6.1 In view of the relatively high impedance of the bell, the use of the telephone type
FPR804-A on party lines should be avoided where possible, unless all parties on the same line are equipped with instruments having bells with similar characteristics.
7. REPLACEMENT PARTS
7.1 It is not proposed to provide special replacement parts for the FPR804-A type telephone and the following arrangements should be made where replacements are necessary.
7.2 Standard equipment is to be used where practicable. For instance, standard
4-conductor line cords and 3-conductor handset cords can be fitted. When a 4
conductor line cord is used the earth connection to terminal “G” is omitted. If a transmitter or receiver
capsule is defective the complete handset is to be changed for a standard handset No. 184 and the FTR handset should be forwarded to the repair centre and held in a pool for use on other telephones of the same type. In eases where replacements cannot be made readily in the field,
the defective telephone should be forwarded to the repair centre to be reconditioned. If repairs should prove impracticable the instruments should be held in reserve for supply of serviceable component parts to other instruments of the same type.