30K-1 Transmitter & 310A Exciter
The Type 30K Transmitting Equipment is a transmitter designed to fulfill the communication requirements of a modern amateur radio station. The unit embodies features which follow the trend of operating practices necessitated by increasingly strict governing regulations and well populated amateur band conditions.
Among these features are: Complete coverage of the 80, 40, 20 15, 11 and 10 meter bands (The 15 meter band is unauthorized at present.);
quick band-change by means of switches; continuous frequency coverage within the amateur bands by means of a highly stabilized master oscillator; frequency calibration within one kc on 40 meters; a speech clipper to prevent overmodulation; and an audio response especially effective in speech communication.
Other features of the 30K Transmitter are: high efficiency; modern tubes and circuits; adequate metering; conservative ratings safety door interlock switch; CW Sidetone oscillator, CW receiver muting and remote control from the operating position.
The Collins Type 310A Exciter Unit, furnished with the equipment, is designed for mounting on the operating table near the operator. With the exception of the filament switch, all controls necessary for turning the equipment on and off are located on the exciter unit front panel.
The transmitter contains antenna tuning equipment which is capable of coupling the power amplifier plate circuit to an untuned transmission line of any impedance or to a tuned line of any multiple of a quarter wave in length. It will also function to couple the transmitter into an unbalanced antenna such as the Marconi, end fed Hertz or end fed Zepp. Antenna tuning and loading controls are located on the front panel. Three pairs of antenna terminals are provided and by connecting jumpers in the BAND switch the bands may be paired up as desired or all bands may be connected to one pair of antenna terminals.
An extra switch section is placed on the power amplifier grid band switch which can be used to operate antenna relays, etc., automatically when the band is changed.
MECHANICAL DESCRIPTION
OVERALL DIMENSIONS
30K Transmitter Unit: 21-7/8″ wide x 66-1/2″ high x 18-15/16″ deep including control knobs on front and door handle and antenna feedthrus on rear.
310A Exciter Unit: 17-1/4″ wide a 10-11/16″ high x 13-7/16″ deep including control knobs on front.
WEIGHT
30K Transmitter Unit – 355 lbs.
310A Exciter Unit – 50 lbs.
FINISH – Both the transmitter unit and the exciter unit are finished in St. James Gray wrinkle finish with polished stainless steel trim.
CONSTRUCTION – The cabinet of the 30K Transmitter Unit is constructed of heavy sheet steel plates formed and welded together. Access to all units is through a full length rear door. Access to the tubes in the Model 310A Exciter Unit is through a hinged top cover.
ELECTRICAL DESCRIPTION
GENERAL – High overall operating efficiency is attained by the use of tetrode and beam power tubes throughout the equipment, where applicable, and by the use of Class B, high level, amplitude modulation. A power input of 375 watts phone or 500 watts CW is possible on all bands. A speech clipper is incorporated in the audio section so that sideband power can be greatly increased without over-modulation. Frequency control is obtained by the use of a highly stabilized, accurately calibrated master oscillator.
RADIO FREQUENCY SECTION
Exciter Unit – The master oscillator, which is heavily shielded and temperature compensated, employs a Type 6SJ7 radio tube. The grid circuit of the master oscillator tube is permeability tuned by a powdered iron slug. The master oscillator tuning control is ganged to the frequency multiplier timing controls and is operated by the main tuning control which is calibrated to within .015 percent. Following the master oscillator tube is a Type 6AG7 tube in an untuned stage which operates on the same frequency as the master oscillator and isolates the oscillator from the frequency multiplier stages.
Following the Type 6AG7 untuned stage is the first tuned doubler amplifier. This stage employs a Type 6AG7 tube also and is tuned to the 80 meter band or twice the frequency of the master oscillator by a variable capacitor ganged with the master oscillator tuning control.
The frequency multiplier stage, a Type 807 beam amplifier tube, is tuned to 80, 40, 30, or 20 meters, as needed, by a variable capacitor and coils selected by a tap switch. The third r-f stage is always used as a doubler except when the final amplifier is operating in the 80 meter band, in which case, the third stage works straight through on 80 meters. The variable capacitors employed to tune the second and third r-f stages are ganged with the master oscillator tuning control. Excitation of the grid of the power amplifier tube in the 30K unit is accomplished by pick-up coils coupled to the second multiplier plate coils and connected to a small coaxial transmission line which connects to the grid circuit of the power amplifier tube. The transmitter is keyed by blocking the grids of the isolation buffer stage and the first doubler stage. All subsequent stages including the power amplifier stage are biased to plate current cut off with no excitation. A keying sidetone oscillator is built into the 310A-3 unit.
Transmitter Unit – Excitation from the second multiplier stage in the exciter unit is carried through a coaxial transmission line and coupled to the power amplifier grid circuit which is tuned to the transmitting frequency. The amount of excitation is controllable from the front panel of the 310A-3 unit, Band switching by means of tap switches is employed in the grid and plate circuits of the power amplifier.
AUDIO SECTION
Transmitter Unit – All audio circuits, which consists of voltage amplifier, speech clipper, high frequency filter, driver and modulator circuits, are located in the transmitter unit. Any high impedance microphone, such as crystal microphone or high impedance dynamic, may be used. The microphone cable connects directly into the rear of the speech amplifier unit in the transmitter.
A Type 6SJ7 and one section of a Type 6SN7 dual triode tube provide audio voltage amplification. A type 6H6 dual diode tube is employed in a clipper circuit to clip both positive and negative audio peaks at a predetermined level to provide greater sideband power without overmodulation. All high, less useful speech frequencies are attenuated by a cut-off filter designed for 4000 cps cut-off, A Type 6B4G tube is used to drive the grids of the Type 75TH modulator tubes. The modulators are capable of modulating the r-f carrier 100% with an audio response which is within 3 db from 100 to 4000 cps.
ANTENNA COUPLING – Because of the great variety of antennas in use in amateur stations an extremely flexible antenna coupling circuit has been incorporated in the transmitter. To meet the complete frequency coverage requirements, it was found advisable to use plug-in units in the antenna tuning apparatus Any type of antenna or transmission line can be tuned with the two plug-in units supplied. Both the tuning and the loading are controllable from the front panel. Either series or parallel tuning can be had with any value of inductance. The ends of the antenna
coil are connected to a pair of rotor contacts in the power amplifier plate band switch, the stator contacts of which can be connected to any one of three pairs of antenna terminals. These stator contacts can be jumpered to get any combination of antenna terminals desired, however, all are jumpered together and connected to the center pair of antenna terminals when shipped from the factory. An extra switch section is placed on the power amplifier grid band switch which can be used to operate antenna relays, etc., automatically when the band is changed.
ACCESSORIES
The Model 30K amateur transmitter is supplied complete with tubes, fuses and interconnecting cables. It will be necessary to have the following apparatus in order to complete the transmitting installation:
1. Any high impedance microphone such as a crystal or high impedance dynamic.
2. A telegraph key.
3. A suitable radiating system.
4. A 115 volt 60 cps power source capable of 1350 watts continuous load.
30K-1 & 310A SPECIFICATIONS
FREQUENCY RANGE ……. 10, 11, 15, 20, 40 and 80 meter amateur bands.
(The 15 meter band is unauthorized at this time.)
FREQUENCY CONTROL ….. Highly stabilized variable frequency oscillator.
TYPES OF EMISSION ….. Amplitude modulated phone and CW. 100% modulation of carrier possible.
NOMINAL CARRIER OUTPUT 250 watts phone, 300 watts CW.
POWER REQUIREMENTS … With a 115 volt 60 cps power source the following
power is required: (Power amplifier loaded to 200 ma CW and 150 ma phone.)
INPUT IMPEDANCE …… High impedance dynamic or crystal.
OUTPUT IMPEDANCE ….. Any antenna impedance which has little reactance.
AMBIENT TEMP RANGE … 0 degrees C (32øF) to 40 degrees C (104øF).
KEYING SPEED ……… 75 WPM.
AUDIO CHARACTERISTICS
(a) Response – Within 3 db from 100 to 4000 cps. A cutoff filter is used
to attenuate all frequencies above 4000 cps.
(b) Amplitude Distortion – Less than 10% total RMS harmonic distortion
(clipper tube removed) up to 100% modulation at 1000 cps.
VACUUM TUBE COMPLEMENT
310A EXCITER UNIT
SYMBOL TYPE FUNCTION
V001 6SJ7 Master oscillator
V601 6AG7 Isolation buffer
V602 6AG7 Frequency doubler
V603 807 Frequency multiplier
V604 807 Frequency doubler
V605 VR105 Voltage regulator
V606 VR105 Voltage regulator
V607 6SL7 Sidetone oscillator
V608 VR150 Voltage regulator
V609 VR150 Voltage regulator
30K TRANSMITTER UNIT
SYMBOL TYPE FUNCTION
V201 4-125A Power amplifier
V301 6SJ7 Audio amplifier
V302 6SN7 Dual audio amplifier
V303 6H6 Speech clipper
V304 6B4G Audio driver
V305 75TH Modulator
V306 75TH Modulator
V401 5R4GY Bias rectifier
V402 5R4GY LV rectifier
V501 866A HV rectifier
V502 866A HV rectifier
30K-1 / 310A CIRCUITRY
MECHANICAL
GENERAL – The complete 30K Transmitting Equipment consists of two units, the transmitter unit and the exciter unit. The transmitter unit is contained in a floor mounting cabinet while the exciter unit is constructed smaller for table mounting. Flexible interconnecting cables are employed between the two units.
The components of the transmitter unit are placed on removable chassis which are constructed of heavy gauge aluminum. All power and control wires between the various units are laced together in nicely formed cables. Connections to the units are made to terminal strips having insulating barriers between the individual screw terminals.
The exciter unit is constructed on an aluminum chassis contained within a steel cabinet which is suitable for table mounting.
The various chassis may be removed from the rear of the transmitter cabinet by removing the control knobs from units so equipped, removing the four bolts which secure the chassis to the mounting cleat, and disconnecting the cable from the terminal strip. (A set of Bristo wrenches is fastened to the rear door for loosening set screws in control knobs.) The transmitter cabinet is equipped with a full length rear door. A glass covered opening in the front panel allows a continuous check on the color of the plate of the power amplifier tube. The meter panel is also behind a glass covered opening in the front panel thereby, in the interest of safety, making a completely dead panel. The antenna current meters are located externally at the top rear edge of the transmitter cabinet. This feature allows shorter connecting leads, making more accurate current readings possible.
ELECTRICAL
GENERAL – A master-oscillator-power amplifier circuit is employed in the 30K Transmitting Equipment to give 375 watts input to the final amplifier on phone and 500 watts input on CW. The final amplifier is high level amplitude modulated with Class “B” modulator tubes.
PRIMARY POWER CIRCUITS – Refer to figure 2-1. The filament transformers T303, T403, T501 and T601 and the bias supply transformer T401 are energized when the FILAMENT switch S103 is closed. Each of the above transformers is protected by a fuse. The primary adjustment taps on filament transformer T403 are brought out to a tap switch S101 which is used to adjust the filament voltage to the PA and modulator tubes. High voltage plate transformer T101 is energized by the operation of plate power relay E401 which is operated when the PLATE switch is closed. Since operating voltage for the plate power relay coil is obtained from the bias power supply, the
primary power cannot be applied to the high voltage transformer until the bias supply is operating thus preventing applying plate power to the power amplifier and modulator tubes when there is no fixed bias. A door switch, S105, operated by the rear access door also interlocks the high voltage power supply to prevent accidental shocks; however, since this unit operates with voltages which are extremely dangerous to life, interlock switches should not be depended upon when working on the unit, rather, completely disconnect the primary source of power by means of a conveniently located main power switch.
The TUNE-OPERATE switch S102 is provided with a large resistor in the TUNE position which reduces the primary power to the high voltage transformer during the tuning procedure. The PLATE power switch in the transmitter unit is interlocked with the POWER switch in the exciter unit in such a manner that the transmitter high voltage cannot be turned ON until the exciter plate power is turned ON.
RADIO FREQUENCY SECTION
Exciter Unit – A Type 6SJ7 tube is employed in a highly stabilized master oscillator circuit to generate the controlling radio frequency voltage. The oscillator circuit is compensated for temperature changes and is entirely enclosed in a heavy aluminum case. The oscillator grid operates in the 1.6875 to 2.0 mc frequency range. The oscillator plate output is in this same range. The oscillator grid circuit is permeability tuned with a powdered iron slug driven by a threaded shaft which is connected to the main tuning dial.
The output of the oscillator is coupled to the grid of a 6AG7 buffer stage. This stage is untuned and operates over the frequency range of the oscillator. The principal purpose of this stage is to isolate the master oscillator from the more powerful frequency multiplier stages which follow. Immediately following the isolation buffer stage is a tuned frequency-doubler employing a 6AG7 tube. This stage doubles the frequency of the oscillator in all cases.
The output of the 6AG7 doubler st&ge is coupled to an 807 frequency multiplier stage by capacitor C607. This stage doubles, triples, or quadruples the frequency as needed. It also operates straight-through when the transmitter output frequency is in the 80 meter band. To get to the 15 meter band, this stage triples the frequency from 80 meters to 30 meters from where the frequency is doubled to 15 meters by the following 807 frequency multiplier tube. The grid excitation to the 807 frequency doubler tube, which follows, is maintained at a nominal value by adding cathode bias to the 807 frequency multiplier tube by me of tap switch section, S601C-1, ganged to the band switch, which switches extra resistance in to the cathode circuit of the 807 frequency multiplier tube when lesser amount of grid excitation to the 807 frequency doubler is needed. One section of the band switch selects the proper multiplier coil while another section of the band switch short circuits the unused coils.
Capacitor C115 couples the Type 807 frequency multiplier stage to the 807 frequency doubler stage. The 807 doubler stage is always used as a doubler except when the transmitter output is in the 80 meter band when it is used as an amplifier on the fundamental frequency. Two sections of the band switch are used in this stage, one to select the proper plate coil and one to short out the unused coils Each output coil has a pick-up coil wound over it to pick-up the excitation power for the power amplifier grid. This pick-up coil is selected by a section of the band switch.
Both 807 tubes have some fixed bias provided by the bias power supply in the transmitter. Additional bias is obtained by the use of grid leak resistors in the grid circuits of both tubes and by cathode resistors in the case of the multiplier tube. Excitation to the power amplifier is controlled by a potentiometer in the screen lead of the output 807.
Plate voltage to all stages in the exciter unit is furnished by a step-up transformer and a 5R4GY high vacuum rectifier. Filament power for all exciter tubes is obtained from a filament transformer T601. The primary circuit of T601 is fused for protection against short circuits. CW Sidetone is obtained through the use of a 6SL7 dual triode in an audio oscillator circuit. One section of the 6SL7 receives plate voltage from the low voltage supply while the other section gets its plate voltage from the voltage drop across the cathode resistor of the frequency multiplier stage which is keyed on CW.
Bias for muting a 75A receiver multiplier stage when the key is down is also obtained from the voltage drop across the frequency multipliers cathode resistor.
Transmitter Unit – The power amplifier for the Collins Model 3OK Amateur Transmitter is located in the transmitter unit. Employing a Type 4-125A tetrode tube, the power amplifier requires a minimum of driving power and needs no neutralizing circuit. Band switching is used throughout the r-f circuits. The power amplifier is used straight-through on all bands. Grid excitation is received from the Model 310A Exciter unit via the link coupling. Both the grid and the plate circuits of the 4-125A tube are turned to the output frequency. Special effort has been made to isolate the grid circuit from the plate circuit to prevent interaction. The band switch sections in both the grid and plate tuning circuits select the proper coils for the band in which operation is desired and, in most instances, short circuits the remaining unused coils.
The control grid of the power amplifier tube is biased to, or beyond, plate current cut-off by voltage from the bias supply. Additional bias is obtained from the voltage drop across grid leak R201. Screen voltage for the 4-125A tube is obtained from the low voltage power supply. Plate voltage for the power amplifier tube is obtained from the high voltage plate supply which employs a pair of 866A mercury vapor rectifier tubes in a full wave circuit.
One half of the plate circuit tuning variable capacitor C207 is employed during operation in the 10, 15, 20 and 40 meter bands while both halves of the capacitor are connected in parallel for 80 meter operation.
AUDIO CIRCUITS
General – The audio system of the transmitter is completely contained in the transmitter cabinet. A high gain microphone amplifier is followed by a two stage audio amplifier which is shunted by a speech clipper tube. The output of the audio amplifier is used to excite a driver stage which drives the grids of the Class B modulator tubes.
100% modulation is attained by the use of any high impedance microphone such as a crystal or high impedance dynamic. The speech clipper clips both the negative and the positive audio peaks, (if clipping is desired), thus prevent overmodulation while allowing a more powerful side band to be transmitted. A cut-off filter attenuates all speech frequencies above 4000 cps.
The plate and the screen of the power amplifier tube are modulated by dual windings on the modulation transformer when using phone emission. When CW emission is employed, the power amplifier plate winding is short circuited and the filaments of the modulator tubes are turned off.
Speech Amplifier Circuits – Refer to Figure 2-2, A 6SJ7 tube, pentode connected, is employed as a high gain voltage amplifier in the input stage of the speech amplifier. The 6SJ7 input tube is followed by a 6SN7 dual triode tube, the first section of which precedes the 6H6 clipper tube. Refer to figure 2-2. The 6H6 clipper tube is shunted across the audio input to the second section of the 6SN7 audio amplifier tube. Notice that the cathode of one section of the 6H6 tube (pin number 4) is operating at a small fixed value of positive potential by virtue of being connected through reactor L301, resistor R310 to a tap on the cathode resistors R311, R312, and R313, This positive cathode potential biases the corresponding diode plate and no current flows through this section of the tube. However, when the magnitude of the negative audio peaks applied to the diode cathode become large enough to overcome the fixed positive potential, current flows through this section of the diode and the negative audio peak is attenuated by the short circuiting action of the diode. Likewise, the cathode of the second section of the clipper tube is returned to a tap on the 6SN7 amplifier cathode resistor which is more positive than the tap where its corresponding plate is attached. Thus the plate of the second section of the 6H6 is more negative than the cathode and no current flows. When a positive audio peak of sufficient magnitude reaches this diode plate the fixed negative bias is overcome and current flows through the second section of the diode and the positive audio peak is attenuated. Because of the above action the audio output of the second section of the audio amplifier tube cannot rise above the fixed level; therefore, it is possible to set the degree of modulation with the Clipper Control R315 and be assured that the percentage of modulation will not rise above the chosen amount.
The output from the second section of the type 6SN7 dual triode tube is coupled to the grid of the modulator driver tube, V304 through capacitor C310 and the Clipper Control R315. V304, a type 6B4G power amplifier tube, drives the grids of the Class “B” modulator tubes through coupling transformer T301.
Modulator Circuit – A pair of Type 75TH triode power amplifier tubes are employed as modulators operating in Class B service. Excitation for the modulator grids is received from the driver tube through the driver transformer T301. Both the screen and the plate of the r-f power amplifier tube are modulated by individual secondary windings on the modulation transformer T302. When switching to CW emission, the modulator filaments are turned off and the power amplifier plate winding in the modulation transformer is short circuited.
Plate voltage for the audio amplifier and the driver stages is obtained from the low voltage supply while plate voltage for the modulator tubes is obtained from the high voltage supply screen voltage for the power amplifier tube is also taken from the low voltage supply. Grid bias for all audio tubes except the modulators is obtained from cathode resistors. The modulators are biased by voltage from the bias supply. A variable resistor, R401, located at the rear of the low voltage power supply unit, is used for adjustment of the modulator bias.
Metering Circuits – All important circuits are metered in the transmitter and exciter units. The power amplifier grid and plate currents, the modulator plate current, the modulator/power amplifier filament voltage, the exciter unit plate voltage, the frequency multiplier grid and plate current, and the frequency doubler (V604) grid and plate currents are metered. Two 3 ampere radio frequency meters to read r-f line current are mounted externally on the roof of the transmitter cabinet to be connected as desired.
Antenna Termination – Refer to figure 3-3. The antenna tuning unit incorporated in the 30K transmitter is a condenser – coil combination which can be conveniently changed from a series to a parallel tuned circuit. The inductance of the coil and the place of antenna feeder attachment can be changed at will, with the result that practically any type of antenna or antenna feeders can be employed. In order to cover the entire frequency range of the transmitter, two sets of plug-in coils are used. One set covers the 10, 11, 15 and 20 meter bands while the other set is used on the 40 and 80 meter bands. The coil units plug into a jack strip mounted on top of the antenna tuning condenser. The antenna coils are split and a moveable link inserted between the sections. This link is actually a continuation of the power amplifier plate tank coil. The connection between the two sections of the antenna coil is actually a small jumper which, when opened, places the antenna tuning capacitor in series with the antenna coil thus making it possible to tune extremely low impedance antennas or transmission lines. When this jumper is closed, the tuning capacitor is in parallel with the coil and high impedance antennas and transmission lines can then be tuned.
In addition to the features already mentioned, it is possible to connect the feed lines to any turn on the antenna coils by means of small contactor arms with which each coil is provided. This allows for perfect transmission line impedance matching.