TR-200-RS TRANSMITTER
INSTALLATION and OPERATING MANUAL INST. 302



(COVER PAGE)
 

INSTALLING AND OPERATING INSTRUCTIONS
For
MARCONI  RADIOPHONE  TRANSMITTER
TYPE TR-200-RS No. 84038

INDEX

GENERAL DESCRIPTION ..............................1
    Rectifier Unit.................................................1 & 2
    Modulator Unit..............................................3
    Transmitter Unit............................................4 & 5
INSTALLATION ................................................5 & 6
ANTENNA SYSTEM.........................................5 & 7
SETTING UP.....................................................7 & 8
TUNING PROCEDURE....................................8, 9, & 10
OPERATION.....................................................10 & 11
CAUTIONS........................................................11
 

CANADIAN MARCONI  COMPANY MONTREAL



 

Page 1

Inst. 302
INSTALLING AND OPERATING INSTRUCTIONS
MARCONI RADIOPHONE TRANSMITTER
TYPE TR-200-RS NO. 84038.

GENERAL DESCRIPTION

The TR-200-RS is a 3-channel crystal controlled transmitter having outputs of 200 and 50 watts when used for telegraph or telephone communication respectively. When used for telephone communication the carrier may be fully modulated from a crystal microphone.  A feature of this transmitter is the carrier control system in which the actual carrier level is varied in accordance with the speech input level to the microphone. This modulation system is optional, the choice being made by a switch on the transmitter unit panel.  A combination of plug-in coils and coil range-switching give the transmitter a wave range of from 50 to 185 metres. The units which make up the complete transmitter are mounted in a steel cabinet, the overall dimensions of which are as follows:- 34” by 19-1/2” in X 17" (height,width and depth). The cabinet which has a hinged rear door to provide access to the valves, coils and crystals, is finished in gray duco and is normally furnished with smooth steel bumpers so that it may be table mounted. For installations where rigid mounting is required, special bolting-down equipment under the type number 57826 can be supplied. The transmitter is made up of three units which are as follows:-
 

Rectifier Unit  Type 57400
Modulator Unit Type 57380
Transmitter Unit Type 81658
Diagram No.  81659 shows schematically the circuit of the complete transmitter.

A panel containing an aerial ammeter can also be supplied on special order, this space normally being filled by a blank panel. A full description of each of the above units follows to enable the operator to fully understand the equipment with which he will work.

Rectifier Unit Type 57400.

This unit is located at the bottom of the cabinet and houses a full-wave rectifier capable of supplying 2100 volts at a load current of 250 ma. For this purpose a pair of 866A mercury vapour rectifier valves are employed, the d-c output being adequately smoothed by a two-section choke input filter which ensures good voltage regulation.

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A bleeder connected across the output of the filter prevents a complete removal of the load. The sole purpose of this rectifier is to provide the plate and screen grid voltages for the power amplifier valve in the transmitter unit. On the panel in front of this unit is mounted the main supply switch which breaks both sides of the a-c supply line to the transmitter, and whose closing lights all the transmitter unit and rectifier unit valves. Also on this panel are two rectangular bullseyes behind which are mounted pilot lamps. The lamp behind the green bullseye is connected to a special winding on the 866-A filament transformer and is used to indicate to the operator that the filaments are being excited. The lamp behind the red bullseye is connected to a similar winding on the high voltage transformer, its lighting indicating that the final starting operation has been completed and that the transmitter is in operation.

Supply voltage is applied to the primary of the high voltage transformer by the closing of contacts on a relay which is mounted on the rectifier unit and which is caused to operate by the closing of the 115 volt a-c supply to its coil. This may be effected by a small external switch which is to be connected to rectifier unit terminals 2 and 10. In this way, remote control of the high voltage is possible. An auxiliary pair of contacts on this relay is used to break the d-c supply to the plates of the oscillator and doubler valves in the transmitter unit when the transmitter is in the “Receive” condition. This will be explained more fully in the section describing the transmitter unit.

Since the valves used in this unit are of the mercury vapour type, the plate voltage must never be applied until the filaments are hot, or until at least 30 seconds have elapsed since the closing of the main switch. Also, when new valves have been inserted, or after the temporary removal of these valves, plate voltage should not be applied until the valves have operated for at least 15 minutes with only the filaments lighted. This process is called “Ageing” and its purpose is to vaporize any particles of condensed mercury that may have been splashed on to the filament or plate during handling. The protective devices incorporated in the unit consist of two fuses in series with the supply line, and a door switch which is for fastening to a bracket mounted on the cabinet just inside the rear door. This switch is connected in series with the operating coil of the relay mentioned above and is arranged so that its contacts open whenever the rear door is opened, thus making it impossible for a person to come into accidental contact with the high voltage output of the rectifier.

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Modulator Unit Type 57380.

This unit is located immediately above the rectifier unit and contains a high gain audio frequency amplifier, the audio frequency rectifier that makes possible the carrier control system, and the rectifier that supplies d-c voltage to the valves in this unit. The amplifier has an overall gain of approximately 75 db and is designed to operate from an American type AG crystal microphone. The audio output voltage is able to fully modulate the transmitter when this microphone is used.
The power supply rectifier section of the unit is controlled by a toggle switch on the panel and employs a type 5Z4 valve in conjunction with a two-section “pi”  type filter.  A separate door switch is provided in this unit, its contacts being in series with the on/off switch. This switch is mounted in a fashion similar to that for the rectifier unit and must be closed by the rear door before the unit can be used.

The output voltage of the microphone is applied to the control grid of a 6J7 valve, the plate of which is resistance coupled to  a type 6C5 valve through a  high resistance potentiometer which acts as a gain control. The latter valve is resistance coupled to a 6F6 power amplifier which transfers its output to a load resistor through an output transformer. The audio voltage developed across this load resistor is connected in series with a fixed bias on the suppressor grid of the output valve in the transmitter unit and causes this grid to swing positive and negative at audio frequency.  Also across this load resistor is connected the primary of the carrier control rectifier transformer, the secondary of which applies an audio voltage to the plates of a type 6X5 valve, Thus, part of the audio power output of the modulator valve is converted into d-c which is dissipated in a resistance connected between the centre tap of the carrier control rectifier transformer and the cathode of the 6X5. When the transmitter switch is set for controlled carrier operation, the voltage drop so obtained is made to oppose an abnormally high fixed bias on the 803 suppressor grid, thereby effectively lowering it to the normal working valve whenever an audio voltage appears at the modulator unit input.

Due to the high gain of this amplifier it is very important that the input and output circuits be well shielded to prevent feedback and self-oscillation. For this reason, the ground connection to the microphone is made through a copper braid that completely encloses the wire from the 6J7 grid to the high side of the microphone.  Care should be taken when connecting the plug to the microphone cord that this braided conductor be connected to the sleeve of the plug.

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Transmitter Unit Type 81658.

Besides housing all the RF circuits of the transmitter, this unit also contains two complete rectifiers, one to produce the bias voltages required by the 803 output amplifier valve and the other to produce the positive voltage required for the operation of the 6A6 oscillator valve. The d-c voltage of the latter rectifier, which employs a type 83V valve, is made adjustable over quite a wide range by the use of a rheostat in series with the positive lead at the input to the filter circuit. This rheostat has its control brought out to the front of the panel where it is designated “Excitation”.  Its function is to vary the output of the oscillator stage by varying the applied plate voltage, and enabling the r-f drive to the 803 amplifier to be adjusted to the value which gives the most satisfactory operation. The plate voltage is removed from the oscillator valve when the transmitter is in the Receive condition by auxiliary contacts on the high voltage relay located in the Rectifier Unit.

These contacts are arranged to break the positive side of the low voltage rectifier output at the input to the filter. However, for test purposes, when it is usually desirable to tune the oscillator stage before the h-t is applied, an auxiliary switch, whose contacts parallel those on the relay, is mounted at the left-hand side of the transmitter panel and is designated "CRYSTAL OSC. PLATE” . When this switch is in the up position its contacts are closed. The bias rectifier employs a type 80 valve and is provided with a potential divider across the filter output. This divider carries a number of adjustable sliders by means of which the 803 control and suppressor grid voltages can be individually adjusted to their proper values. The control grid voltage remains constant at 120 volts negative for all methods of operation, but the suppressor grid must be varied from about 40 volts positive in the CW condition to about 120 volts negative in the Phone condition, and to about 250 volts negative in the controlled carrier condition. The changing of these voltages is the principal function of the three-position switch located at the right-hand side of the panel engraved “CW-PH-CC". The transmitter is keyed (when the latter switch is in the CW position by the insertion of a plug, to which is connected a telegraph key, into the jack located at the extreme right of the panel.  This puts a very high negative bias on the suppressor grid which causes the valve to cut off. When the key is pressed,  this voltage changes to a positive value which allows normal operation of the valve. This unit is also equipped with a door switch, mounted as described for the rectifier unit, and connected in series with the supply line to the rectifier transformers.

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The oscillator stage is tuned by a tank circuit consisting of Q tapped plug-in coil .and one of three small variable condensers. One condenser is used for each channel, thereby making it possible to pre-tune the oscillator  on three set  frequencies. These condensers are switched in and out of circuit by a three-position tap switch, other sections of which are utilized to select one of three crystals, and to adjust the range of the tank circuit by short-circuiting a given number of turns on the coil, thereby changing its inductance value. This switch is located at the lower centre of the transmitter unit panel. The power amplifier stage is similarly tuned by a tapped plug-in coil and one of three condensers, these latter being switched in and out of circuit by the heavy duty tap switch located immediately above the oscillator range switch.

 A second section of this switch is used to short circuit portions of the p-a coil as was described for the oscillator coil, while a third section is employed to switch the loading taps on this coil, those taps being, in effect, the transmitter end termination of the antenna or feeder. The output power of the transmitter is thus transferred to the antenna by the simple expedient of tapping the antenna directly to the p-a coil. However, since the characteristics of an antenna vary with frequency, the point at which it must be tapped on to the coil will be different for each frequency. Therefore, three taps are provided, one for each channel, which may be soldered directly on to the coil at the point required for correct operation on each frequency.  The clip provided with this coil is intended only as a means of tapping during the preliminary adjustments and should be removed and the lead soldered to the appropriate turn when the proper point has been found.

The three oscillator tuning condensers  are 'located behind the panel for screwdriver adjustment, access being obtained through hole which is normally hidden by a small cover plate. The three tuning condensers, also arranged for screwdriver adjustment, are located near the top of the transmitter unit panel and are provided with locking devices to hold them in place when the correct adjustment has been found. They are made adjustable through small holes, one for each condenser, which holes are normally filled by nickel-plated push-in plugs.

INSTALLATION

After unpacking the transmitter and accessories, examine them carefully for possible  damage in transit. For convenience and protection during shipment, the rectifier unit is removed from the cabinet and packed separately. First then, remount this unit in its proper position, using the screws provided, and fastening the main switch and the pilot lamp sockets to the front

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panel. Now connect the cable from the other units  to the terminals indicated by the tags on the individual wires. Mount the door switch in the bracket provided for it in a similar fashion to the door switch on the other units. This switch should project just enough  that closing of the rear door will operate it but will not cause the door to bulge. Place the transmitter in the operating position which should be arranged so that the back is accessible for the insertion of valves, crystals, and coils, and the making of any necessary internal adjustments.

The 115-volt 60-cycle power supply should be run in BX cable from the service switch to the point of entry into the cabinet. Two methods of entry are possible. The first and preferable method is to run the BX cable up through a hole in the bench or table to the hole located in the bottom of the cabinet. This method has the advantage of making a neater installation since the supply wiring is concealed. If, however, for any reason this is not desirable, another hole is provided in the back of the cabinet to which the cable may be run over the top of the table. In the latter method, the plate fastened to the back screen to conceal this hole must be removed and discarded. A standard conduit fitting is provided to secure the cable to the case whichever method of entry is used. Connect the supply wires to rectifier unit terminals 6 and 7. At this junction also connect the remote switch to control the h-t rectifier. This switch may be of the toggle variety and can be mounted in the most convenient place, for example, let into the table beside the telegraph key or mounted on the panel of the receiver. The leads from it may be run in lamp cord and will preferably enter the unit through the second hole in the bottom of the cabinet. They should be connected to rectifier unit terminals 2 and 10.

ANTENNA SYSTEM

The TR-200 is designed to operate with a single wire or voltage fed antenna system tapped directly to the plate coil. This is made possible by the use of a shunt feed system for the output valve, enabling one side of the output tank circuit to be tied directly to ground. While almost any length of wire may be made to radiate on almost any frequency, best results will be secured with an aerial whose dimensions are such that maximum efficiency is provided on the operating frequency. It is therefore advisable to design the aerial so that this condition is fulfilled when the transmitter with which it is working is operating on the frequency which will be used most. Then, on this frequency, the system will operate as a horizontal dipole with a non-radiating feeder.

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On all other frequencies, unless those happen to be harmonics of the fundamental aerial frequency, it will operate as a Marconi antenna.

The approximate dimensions of a horizontal dipole aerial with a single wire feeder for any frequency between 2 and 6 megacycles can be calculated from curve sheet 3133, a copy of which will be found in the folder. To obtain the best possible impedance match on any frequency except the one to which the aerial is cut, an impedance matching network and coupling system is usually necessary. Units for this purpose can be supplied on special order for any aerial system.

Assuming that an aerial is erected, the feeder should be brought into the building through an approved insulator and connected to the transmitter insulator which connects to the arm of the feeder tap-changing switch section. Connect the ground wire to the other insulator. An ideal ground should be formed by burying a number of copper plates in moist earth in the form or u circle about the transmitter, the circle having a radius of 30 to 40 feet. The plates should all be connected to a common point at the centre of the circle by radial wires and a single conductor run from this common point to the ground terminal on the transmitter. Where the expense of such an elaborate system is not warranted, the best available ground should be used which, in some cases, may be a cold water pipe.

SETTING UP

Assuming that the transmitter has been completely re-assembled and connected as outline above, the next operation should be the insertion of all valves, crystals, and coils in their respective sockets. The transmitter employs the following valves:-

Transmitter Unit 1 - RVC-80 - Bias rectifier.
                            1 - RVC-83V- Low voltage rectifier.
                            1 - RVC-6A6- Oscillator.
                            1 - RVC-803- Modulated amplifier

Modulator Unit   1 - RVC-5Z4- Rectifier
                            1 - RVC-6X5- C.C. rectifier.
                            1 - RVC-6J7- Audio amplifier.
                            1 - RVC-6C5- Driver.
                            1 - RVC-6F6- Modulator.

Rectifier Unit      2 - RVC-866A - High voltage rectifier
                            2 - 6.3 V. Mazda pilot lamps min. bayonet base.

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The location of all valves can be determined by reference to the various units on which the valve type numbers are stencilled beside each socket. The oscillator coil plugs into the socket immediately in front of the 6A6 oscillator valve and is covered by a large cylindrical shield. The crystals plug into sockets in the centre of the transmitter unit base, these sockets being numbered 1, 2 and 3. These numbers refer to the channel number and correspond to the numbers on the oscillator and power amplifier tap switches. When inserting the crystals, make certain that the crystal pin marked GND is located nearest the centre of the chassis, as otherwise false operation may result.

The tuning condensers are also referred to by number, these numbers also corresponding to number of the channel in which they are connected. The power amplifier condensers are marked by small circular number plates set into the front panel beside each condenser, while the oscillator condensers are marked by numbers stomped on the panel underneath the cover plate.

The crystals should be inserted in sockets as specified on the Transmitter Test Record which will be found tied to the unit.

Providing the proper crystals were available, the transmitter will have been thoroughly tested at the factory and all tuning controls will have been left in their proper adjustment. The tuning of all circuits should be checked, however, to ensure against variation during shipment.

TUNING PROCEDURE

Assuming that all valves, coils, crystals, etc. are in position and that the wiring has been checked and found to be in order, the transmitter may be put into operation, first making sure that the external switch controlling the high voltage rectifier is open and that the rear door is closed. Put all toggle switches in their OFF positions and the CW-PH-CC switch in the PH position. Now close the main switches on the rectifier unit panel. This should light all the filaments in the rectifier and transmitter units, and also light the pilot lamp behind the green bulls-eye. Note the time as the high voltage rectifier valves must be left in this condition to age for at least 15 minutes, as already explained. In the meantime the tuning of the oscillator circuits may ho checked. Remove the cover plate at the lower right-hand side of the transmitter unit panel exposing the condenser controls. The upper control is number 1 while numbers 2 and 3 are the lower loft and right controls respectively.

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With the oscillator range switch on position 1, move the CRYSTAL OSC. PLATE switch to the up position and with a screwdriver rotate the number 1 oscillator condenser until the POWER AMP GRID meter reaches a maximum  reading. Manipulate the EXCITATION control until this reading lies between 15 and 20 ma. Leaving condenser 1 in the position just found, repeat the above in positions 2 and 3 of the oscillator switch and tuning with the appropriate condensers. Then return both range switches to position 1.

As soon as the 15 minute ageing period has elapsed the tuning of the power amplifier stage may be started. Remove the three cover plugs over these condensers and loosen the nickel-plated locking screws on each condenser. Now close the switch controlling the high voltage rectifier and using a screwdriver quickly rotate the number 1 condenser until a sharp dip in the POWER AMP PLATE meter reading occurs. Set the condenser at the point required to reduce the reading to minimum. The exact value of the plate current in this condition is not very important but normally it will not exceed 30 or 40 ma. Resonance should now be found on the other two frequencies in the method outlined for channel l. The grid current should be re-adjusted each time  by means of the EXCITATION  control to approximately 15 ma.

Now shut down the transmitter, open the rear door and attach the power amplifier coil tapping clip to the flexible feeder tapping lead that is appropriate to channel l, i.e. the lead nearest the rear of the coil. Then tap this lead to, say, the third turn from the roar of the coil taking care that the lead is kept well out in the open and that the clip does not short-circuit two adjacent turns on the coil. Re-close the rear door, set the switches in position 1 and restart the transmitter, it now being necessary to wait only 30 seconds before switching on the high voltage. Retune the p-a tank circuit using number 1 condenser and note the plate current reading obtained. When correctly loaded in the Phone condition, the plate current should have a value of from 75 to 80 ma., so the tap on the coil should now be moved accordingly. Thus, if the increase in plate current from the unloaded condition was small, the loading tap must be moved along the coil towards the front of the unit a considerable number of turns. If, on the other hand, the reading was higher than 80 ma, the tap should be moved back slightly. On the higher frequencies especially, a change of half a turn may be the difference between correct and incorrect loading. In this way the tap should be moved from turn to turn until the plate current reading falls within the limits stated above, taking care to shut down the transmitter before, and to retune the output tank after every adjustment. The grid current should be maintained at approximately 15 ma.

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When a loading tap position has been found that will comply with the above requirements, switch over to “CW" (It is not necessary to plug in a key since the contacts of the key jack are short circuited until a plug is pushed into it). This should increase the plate current to a value that falls between the limits of 130 and 160 ma. Chock that inserting the key plug reduces the plate current to zero, or practically zero, and that pressing the key restores the previous plate current value.

Now switch over to “CC”. The plate current should fall to a value approximately the same as that obtained with the output circuit unloaded. The adjustments can now be assumed to be correct for this frequency. Therefore shut down the transmitter, remove the output tank coil and, removing the tapping clip, solder the flexible load to the turn which was found to provide the correct loading. Here again, it is very important that the solder does not flow into the coil and short circuit one or more adjacent turns.

It is now necessary to repeat the procedure outlined in the above two paragraphs on the other two frequencies, using switch positions 2 and 3 and the approximate condensers and flexible tapping leads. In this case note that the load tap may be well up on the coil since in some positions the rear section of the coil is short-circuited, this shorted section then being effectively out of circuit.

Having completed the adjustments satisfactorily on all channels, the CRYSTAL OSC. PLATE switch should be moved to the down or OFF position and the transmitter operation checked on all three frequencies using only the external switch to control both oscillator and p-a voltages. If it is found that the crystal does not start oscillating each time the switch is closed, (indicated by an absence of grid current) back off the oscillator tuning condenser for that frequency slightly from its maximum output position. If the overall operation now seems satisfactory, lock up the
p-a condensers, replace their dummy plugs and replace the plate over the oscillator tuning condensers.

The sliders on the bias rectifier potential divider are set at the factory during the routine tests on the transmitter. These should not be moved unless a voltmeter is available as an aid in resetting them.

OPERATION.

CW. In order to key the transmitter turn the CW-PH-CC switch to “CW" and insert the key plug into the jack so marked. As the transmitter uses the grid blocking method of keying a voltage of about 300 volts is present on the key. While this is by no means dangerous, as only a few milliamperes of current can be drawn, it is unpleasant and caution should be exercised to avoid contact with it. This voltage appears when the filaments are lighted.
 

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PHONE. For phone operation it is only necessary to turn the switch to “PH”, close the modulator supply switch, plug in the crystal microphone, and, after waiting for the modulator valves to heat, advance the gain control until normal speech into the microphone fully modulates the carrier. If an r-f ammeter is available to measure the aerial current, the determination of 100% modulation will be simplified, since when this occurs, the aerial current will be approximately 22% higher than with no modulation. This, of course, applies only if the modulation is in the form of a sustained tone, such as may be produced by whistling into the microphone. If an ammeter is not available, the only safeguard against overmodulation is to keep the gain control just below the point at which the plate current flicks on speech peaks.

CC. For controlled carrier operation, it is only necessary to turn the switch to “CC". This may be done while the transmitter is operating. In this condition, the strength of the carrier is controlled by the instantaneous value of the modulation. In other words, with no modulation, the actual carrier strength is about 5 watts, rising to its normal value of 50 watts under full modulation. When operating in this condition, the modulator gain control should be left in the position found to be best for normal phone operation. While normal phone operation should generally be used, since the quality is better, the carrier fluctuation characteristic of the CC condition is often a great aid in reducing interference.

CAUTIONS.

1. Never close the high voltage rectifier control switch before the filament switch, or until the filaments have heated for at least 30 seconds.

2. Never exceed a plate current of 80 ma when operating on Phone.

3. Never exceed a plate current of 175 ma when operating on CW.

4. Always retune the output tank circuits for resonance after every antenna adjustment.

5. Never allow the antenna tap on the plate coil to touch more than one turn at a time.

6. Never run the modulation gain control high enough to cause a violent movement of the plate current meter.

7. THE POWER SUPPLY IN THIS TRANSMITTER DEVELOPS 2100 VOLTS D-C. THIS VOLTAGE IS HIGH ENOUGH TO CAUSE SERIOUS INJURY OR DEATH. DO NOT TRY TO MAKE THE DOOR SWITCHES INOPERATIVE SO THAT THE TRANSMITTER MAY BE OPERATED WITH THE REAR DOOR OPEN. THE DOOR SWITCHES ARE PROVIDED FOR YOUR PROTECTION.

Canadian Marconi Company, Montreal, June 16, 1939.



Contributors and Credits:

1) Manual provided by: Ted Thorpe, VE3HPL <ve3hpl@in-ed-tech.com>

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Mar 3/08