32S-3/3A Transmitter



The Collins highly flexible 32S-3 Transmitter covers all the amateur bands between 3.4 mc and 30 mc with a power input of 175 watts PEP on SSB or 160 watts on CW. It has a nominal output of 100 watts.

All of the dials and controls are clearly marked and human- engineered for operational efficiency. In the 32S-3, Collins design engineers have produced a transmitter with a minimum number of controls to offer you precise tuning.

The 32S-3 can also be adapted for RTTY operation because of the high degree of stability of the unit. Grid block keying in CW with adjustment of characteristic from "soft" to "hard" for individual operator is provided.

A combination of features found in no other transmitter on the amateur market gives you that top performance which you expect - and get - only in Collins transmitters. These features include:

DUAL CONVERSION with the high frequency oscillator crystal- controlled, and low frequency oscillator variable, resulting in a frequency stability for Collins transmitters which has become the standard of the amateur field.

COLLINS AUTOMATIC LOAD CONTROL which aids in preventing over modulation and provides up to 10 db compression for higher average talk power.

COLLINS RF INVERSE FEEDBACK for improved linearity and reduction of distortion products and splattering.

CW SPOTTING CONTROL which allows the 32S-3 frequency to be quickly and easily adjusted to zero beat with a signal tuned on the receiver. The carrier is momentarily keyed in the low level stages without disabling the receiver. A level control facilitates zero adjustment.

COLLINS MECHANICAL FILTER providing a clean, clear signal without need for adjustment, additional audio filters, or special microphones.

The 32S-3 comes equipped with the crystal sockets, crystals and bandswitch positions for eleven 200 kc bands. Crystal sockets and bandswitch position also are provided for two additional 200 kc bands between 28 mc and 30 mc. A fourteenth position, corresponding to the WWV position on the receiver, can be used for an additional 200 kc band in the 9.5-15.0 mc range, if desired. Regulation of oscillator voltages insures high frequency stability.

The 32S-3 can be operated on any frequency in the range of 3.4-30 mc, except 5.0-6.5 mc, by installing an appropriate crystal. Plug-in crystals are available to convert any of the above amateur band channels to out-of-band channels. Easy access is provided to crystal oscillator patch cables from top of cabinet. Front panel selection of receiver VFO or transmitter VFO provides optional transceiver operation at the flick of a switch.

While the 32S-3 provides ample RF power for excellent communication, it can be used without modification to excite the Collins 30L-1 or 30S-1 Linear Amplifier.


FREQUENCY RANGE: 3.4-5.0 and 6.5-30.0 mc; bands are as follows:

     80 meters - 3.4-3.6 mc, 3.6-3.8 mc and 3.8-4.0 mc.
     40 meters - 7.0-7.2 mc and 7.2-7.4 mc.
     20 meters - 14.0-14.2 mc and 14.2-14.4 mc.
     15 meters - 21.0-21.2 mc, 21.2-21.4 mc and 21.4-21.6 mc.
     10 meters - 28.5-28.7 mc.

MODE: SSB (either sideband selectable) or CW.

TYPE OF SERVICE: SSB continuous; CW 50% duty cycle.

POWER REQUIREMENTS: 115 v, 50-60 cps. Power can be delivered by an
    external supply which must furnish 800 v dc at 220 ma for PA
    plates, 275 v dc at 175 ma, for PA screens and low voltage plates.
    Bias voltage adjustable between -60 v and -80 v dc; 6.3 v ac at
    7.7 amps or 6.0 v dc at 6.0 amps or 12.0-14.0 v dc at 3.0 amps
    or 24.0-28.0 v dc at 1.5 amps.

    CW, key closed, 320 watts ac or 25 amps at 12 v. SSB, no
    modulation, 230 watts ac, 15 amps at 12 v. SSB, speech modulated,
    255 watts ac, 20 amps at 12 v.

PLATE POWER INPUT: 175 watts PEP on SSB; 160 watts on CW.

POWER OUTPUT: 100 watts PEP (nominal) into 50 ohms.

    unwanted sideband --50 db; oscillator feed-through and/or mixer
    products -50 db. Second harmonic -40 db.
    Third order distortion -30 db.

NOISE LEVEL: 40 db below one tone carrier.



ALTITUDE: 0-10,000 ft.

PROTECTIVE DEVICES: Primary fuses provided in the power supply
    to be used with the equipment.

SIZE: Transmitter with feet - 14-3/4" W, 7-3/4" H, 12-1/2" D.

WEIGHT: 16 Lbs.

FREQUENCY STABILITY: Within 100 cps after warm-up.


BACKLASH: Not more than 50 cps.

VISUAL DIAL ACCURACY: 200 cps on all bands.

OUTPUT IMPEDANCE: Variable, 50 ohms nominal, capable of matching 2:1 SWR.

CW SIDETONE: Provision for monitoring keying in receiver.
    Sidetone level is adjustable.

KEYING CHARACTERISTICS: Keying is free of chirp and clicks. Modified
    break-in CW provided. Keyed carrier used for CW keying.
    Envelope rise and decay time adjustable.

AUDIO INPUT: High impedance microphone or phone patch.

AUDIO FREQUENCY RESPONSE: 300-2400 cps +6 db.

    and is capable of 10 db compression.

RF FEEDBACK: Approximately 10 db of RF feedback around PA and driver
    for improved PA linearity.

Under the hood...

[Internal View]


Type 32S-3A is a 175-watt input transmitter covering 3.4 to 30 MHz. The transmitter uses filter type sideband generation and heterodyne exciter principles. A crystal-controlled bfo, crystal-controlled high-frequency oscillator, and highly stable vfo form a double conversion circuit. The low- frequency if is 455 kHz, and the high-frequency if is 3.055 MHz with a 200-kHz wide passband, from 2.955 to 3.155 MHz. The 32S-3A may be connected in transceiver service with 75S- ( ) receivers.


Microphone or phone patch audio is coupled in the grid of first audio amplifier V1A, amplified, and coupled to the grid of second audio amplifier V1B. Output from V1B is coupled to the grid of cathode follower V2A across MIC GAIN control. Output from the cathode follower is fed to the balanced modulator. In TUNE, LOCK KEY, and CW positions of the EMISSION switch, output from the tone oscillator, V11B, is fed to the grid of the second audio amplifier. Tone- oscillator signal is taken from the plate of V1B to the grid of the VOX amplifier and the CW sidetone jack, J19.


Audio output from the cathode of V2A is fed to the junction of CR3 and CR4. In USB and LSB positions of the EMISSION switch, the bfo voltage is fed to the junction of C187A and C187B. (In TUNE, LOCK KEY, and CW positions of the EMISSION switch, the bfo voltage by-passes the balanced modulator, if amplifier, and mechanical filter and is fed directly to one of the first mixer cathodes.) Output from the balanced modulator consists of both upper and lower sidebands and is coupled through if transformer T2 to the grid of if amplifier V3. Output from if amplifier V3 is fed to mechanical filter FL1. The passband of FL1 is centered at 455 kHz.

This passes either upper or lower sideband depending upon the sideband polarity selected when the EMISSION switch connects bfo crystal Y12 or Y13.


The 455-kHz single-sideband signal is fed to the first balanced mixer grids in push-pull; the plates are connected in push-pull; and the vfo signal is fed to the grids in parallel. The mixer suppresses the vfo signal and translates the 455-kHz single-sideband signal to a frequency between 2.955 and 2.155 MHz. This is the bandpass if. The coupling network between the plates of the first mixer and the grid of the second balanced mixer is broadbanded to provide a uniform response to the bandpass if. The bandpass if signal is fed to one of the grids of the second balanced mixer, and the high-frequency injection signal from the crystal oscillator V12 is fed to the signal input cathode and to the other grid. This arrangement suppresses the high-frequency injection signal within the mixer and translates the bandpass if signal to the desired operating band.


The slug-tuned circuits coupling V5 to V6, V6 to V7, and V7 to the power amplifier are ganged to the EXCITER TUNING control. The signal is amplified by rf amplifier V6 and driver V7 to drive power amplifier V8 and V9. Output from the power amplifier is coupled by a pi-network to the antenna through contacts of transmit-receive relay K2. Negative rf feedback from the pa plate circuit to the driver cathode circuit permits a high degree of linearity at the high power level of the pa tubes. Both the driver and pa stages are neutralized to ensure their stability.


ALC Circuit

Detected audio-frequency voltage from the power amplifier grid circuit is rectified by CR5 and CR6, and the negative dc output is fed to the ALC bus. A fast attack, slow release, dual time constant is used to prevent over-driving on initial syllables and to hold gain constant between words. The fast time constant ALC is applied to V6, and the slow time constant ALC is applied to V3. If the companion 30S-1 or 30L-1 Power Amplifier is used with the 32S-3A ALC, output from the 30S-1 or 30L-1 is fed back to the ALC bus.

VOX and Anti-VOX Circuits

Output from second audio amplifier V1B is fed to the grid of VOX amplifier V14A through VOX GAIN control R74. This audio input is amplified by V14A and rectified by VOX rectifier V10B. When the positive output of V10B is high enough to overcome the negative bias on V11A grid, the VOX relay is actuated to turn the transmitter on. Receiver output is fed from J13 through ANTI VOX GAIN control R85 to the grid of anti-VOX amplifier V14V. Output from V14B is rectified by anti-VOX rectifier V10A to provide the negative bias necessary to keep the transmitter disabled during receive periods. The anti-VOX circuit provides a threshold voltage to prevent loudspeaker output (picked up by the microphone) from tripping the VOX circuit into transmit. ANTI VOX GAIN control R85 adjusts the value of the anti-VOX threshold so that loudspeaker output will not produce enough positive dc output from the VoX rectifier to exceed the negative dc output from the anti-VOX rectifier and cause V11A to actuate VOX relay K1. Speech energy into the microphone will cause the positive VOX voltage to overcome the negative anti-VOX voltage and produce the desired action of K1. Contacts of relay K1 control relay K2, key line, PA and driver screens, receiver muting circuits, and oscillator plate voltages.

Manual Gain Control

The MIC GAIN control is a dual potentiometer. Section R8A controls microphone gain during SSB operation. Section R8B is a cathode potentiometer which controls the gain of rf amplifier V6 during CW, TUNE, or LOCK-KEY operation. This control will be set more clockwise in these modes than it will be in the USB or LSB modes.


Tone Oscillator

The tone oscillator is used for VOX circuit actuation and sidetone generation during CW operation. It consists of an RC phase-shift oscillator operating at approximately 750 Hz. Its output is amplified by the second audio amplifier which then supplies the sidetone output and also activates the VOX circuitry to provide CW break-in. In TUNE and LOCK KEY, the oscillator is used in conjunction with the second audio amplifier to give sidetone output. The oscillator is turned on when EMISSION switch section S8C is in TUNE, LOCK KEY, or CW position.

Beat-Frequency Oscillator

The bfo is crystal controlled at either 453.650 kHz or 456.350 kHz depending upon whether Y12 or Y13 is selected by EMISSION switch section S8F. These crystal frequencies are on either side of the passband of mechanical filter FL1, so the carrier frequency is placed approximately 20 dB down on the skirts of the filter response. This carrier suppression is in addition to the 30-dB minimum suppression provided by the balanced modulator.

Variable Frequency Oscillator

The vfo uses fixed capacitors, a permeability tuned variable inductor, and fixed inductors to provide the tuning range of 2.5 to 2.7 MHz. The frequency-determining network is composed of capacitors C301, C302, C303, and C305, and inductors L301, L302, and L303. Capacitor C303 is paralleled by trimmer capacitor C308 and diode CR301 connected in series. A dc bias voltage is applied to the diode through rf isolation resistor R303. When LSB emission is selected, negative bias is applied to CR301 which switches C308 out of the circuit. Selection USB emission applies positive bias to CR301, causing it to conduct which switches C308 into the circuit. Proper adjustment of C308 shifts the vfo output frequency by an amount equal to the frequency separation of the two bfo crystals. This allows selection of either sideband without changing the suppressed carrier frequency of the exciter rf output.

High-Frequency Crystal Oscillator

High-frequency crystal oscillator V12 is crystal controlled by one of 14 crystals (11 supplied and 3 optional) selected by BAND switch S14, or by one of 14 crystals (none supplied) selected by BAND switch S11. Output from the high-frequency crystal oscillator is fed to the second mixer. This frequency is always 3.155 MHz higher than the lower edge of the desired transmit band. This high-frequency injection signal is the crystal fundamental frequency for all desired output signals below 12 MHz, but for operating frequencies higher than 12 MHz, the crystal frequency is doubled in the plate circuit of the oscillator.


Grid-block type keying is used for CW operation in the 32S- 3A. With the key up, a negative voltage is applied to the grids of a second audio amplifier and the second mixer. This prevents the amplified tone oscillator output from actuating the VOX circuitry and also cuts off the second mixer. The keying time constant of the second audio amplifier is fast attack and slow release with R127 and C115 determining the fast attack and R125 and C115 determining the slow release. The keying time constant of the second mixer is slow attack and slow release with the slow attack determined by R123, R124, and C81. R123, R124, C81, and C115 determine slow- release time. When keying takes place, second audio amplifier and the VOX circuitry are actuated before the second mixer. The release times of the second audio amplifier and second mixer are approximately the same. The VOX TIME CONSTANT control adjusts release time of the VOX circuitry to permit fast ON-OFF keying.

Variable resistor R123 provides a choice between the extremes of "hard" and "soft" keying. This control and its effect are described fully in paragraph 2.1.3. Capacitor C115 determines, to a large extent, the release time of the "break." An additional effect is that the larger this capacitor, the greater is the "lag" introduced which is characterized by the bell-like type of keying well known to CW operators. The values of C115 and R123 have been chosen to produce generally acceptable keying. While it is not suggested the value of C115 should be changed, if the operator desires an increased amount of the bell-like characteristic, a slightly larger value will produce the effect. The additional "lag". however, will reduce the maximum speed at which the 32S-3A may be satisfactorily keyed.

An additional amplifier following an exciter can change keying characteristics. A well-designed and adjusted linear amplifier, such as the 30L-1 or 30S-1, has a negligible effect on keying. A class C amplifier and its associated power supply, however, will generally have considerable effect, because cutoff bias must be overcome before the signal is amplified, thus causing a sharp wavefront. Proper adjustment of the keying waveshape can only be made with the exciter driving the class C amplifier.

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This Home Page was created by wa3key, Saturday, March 16, 1996
Most recent revision Saturday, March 16, 1996