SBE SB-36 Operation Manuals

SBE SB-36 OPERATION MANUAL

SB-36 OPERATION MANUAL

Remastered by NoobowSystems Lab. Tomioka, Japan 2003 Rev.00

http://www.noobowsystems.com

PRELIMINARY VERSION

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SBE SB-36 OPERATION MANUAL

WARRANTY

Linear Systems, Inc. warrants equipment manufactured by it to be free from defects in
material or workmanship and agrees to repair such equipment which under normal use
and service, develops defects arising from the fault of the manufacturer. Equipment must
be returned transportation prepaid within 90 days from the date of original purchase, and
unless the warranty card has been filled in and returned within ten days of original
purchase, the warranty shall be void.

This warranty does not apply to equipment which (1) has been repaired or altered by
anyone in any way so as, in our judgment, to injure its stability or reliability, (2) has been
subject to misuse, negligence, or accident, (3) has had the serial number altered defaced,
or removed, or (4) has been connected, installed, adjusted otherwise than in accordance
with our written instructions.

The foregoing is in lieu of any other warranty or liability expressed, implied, or statutory
and in no event shall Linear Systems, Inc. be liable for special or consequential damages.
Linear Systems, Inc. neither assumes nor authorizes any person to assume for it any other
obligation or liability in connection with this equipment.

LINEAR SYSTEMS, INC.
220 Airport Boulevard
Watsonville, California 95076
[phone]

NoobowSystems Lab. Remastering Information

Revision 0.0 Aug.11, 2003 Preliminary release, some pages are missing.

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SBE SB-36 OPERATION MANUAL

TABLE OF CONTENTS

Paragraph Page

Section I
General Description

1.1

General

1

1.2

Specifications 1

1.2.1 General 1

1.2.2 Transmitter 1

1.2.3 Receiver 2

Section II
In starvation

2.1 General 3

2.2 Fixed Station 3

2.3 Antennas 3

2.4 Linear Amplifier 3

Section III
Operation

3.1 Operation Instructions 4
Section IV

Operating Procedure

4.1 Receiver Operation 11

4.2 Transmitter Tuning Procedure 11

4.3 CW operation 12

Section V
Theory of Operation

5.1 General 13

5.2 Transmitter circuitry 13

5.3 Receiver Circuitry 16

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SBE SB-36 OPERATION MANUAL

Table of Contents

1.0 INTRODUCTION...........................................................................................................................5

1.1 GENERAL............ ............. . ..................... ......................................................................................5

1.2 SPECIFICATIONS.............. ............... . ............... . ............... . ............... . ............... . .........................5

1.2.1..................................................................................................................................General

.....................................................................................................................................................5

1.2.2............................................................................................................................Transmitter

.....................................................................................................................................................6

2.0 INSTALLATION............................................................................................................................7

2.1 GENERAL............ ............. . ..................... ......................................................................................7

2.2 FIXED STATION....................................................................... ....................................................7

2.3 ANTENNAS........... . ................................................. . ................................................. ...................7

2.4 LINEAR AMPLIFIER.....................................................................................................................7

3.0 OPERATION....................................................................... ..........................................................8

3.1 OPERATING INSTRUCTIONS.......................... .............. ............. . .............. .................................8

3.1.1.............................................................................................................................................8

4.0 OPERATING PROCEDURE............ ............. . .......................... ............. . .....................................14

WARNING:............................................... .........................................................................................14

4.1 RECEIVER OPERATION...........................................................................................................14

4. 2 TRANSMIT TUNING PROCEDURE........................................ ..................................................14

4. 3 CW OPERATION.......................................................................................................................15

5. 0 THEORY OF OPERATION........................................................................................................17

5. 1 GENERAL.......................... ........................................................................................................17

5.1.1...........................................................................................................................................17

5. 2 TRANSMITTER CIRCUITRY..................... ........................ ........................ ................................18

5.2.1.........................................................................................................Transmitter Signal Path

...................................................................................................................................................18

5.2.2......................................................................................................Automatic Level Control

...................................................................................................................................................19

5. 3 RECEIVER CIRCUITRY....................... ......................................................................................19

5.3.1.............................................................................................................Receiver Signal Path

...................................................................................................................................................19

5.3.2........................................................................................................................Noise Blanker

...................................................................................................................................................20

5.3.3........................................................................................................Automatic Gain Control

...................................................................................................................................................20

5.3.4.........................................................................................................................VOX Keying

...................................................................................................................................................21

5.3.5..................................................................................................Frequency Mixing Network

...................................................................................................................................................21

5.3.5.1................................................................................................................Carrier Oscillator

...................................................................................................................................................22

5.3.5.2...................................................................................................................VFO Oscillator

...................................................................................................................................................22

5.3.5.3.................................................................................................High Frequency Oscillator

...................................................................................................................................................23

5.3.5.4 Side Tone Oscillator.....................................................................................................23

5.3.6..................................................................................................................................Counter

...................................................................................................................................................24

5.3.7........................................................................................................................Power Supply

...................................................................................................................................................25

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SBE SB-36 OPERATION MANUAL

6. 0 MAINTENANCE......................... . ...............................................................................................27

6. 1 INTRODUCTION........................................................................................................................27

6.2 PREVENTATIVE MAINTENANCE..............................................................................................27

6.2.1..................................................................................................................................General

...................................................................................................................................................27

6.2.2......................................................................................................................Cover Removal

...................................................................................................................................................27

6.2.3................................................................................................................................Cleaning

...................................................................................................................................................27

6.2.4............................................................................................................................Lubrication

...................................................................................................................................................28

6.3 TROUBLESHOOTING................................................................................................................28

6.3.1.................................................................................................Troubleshooting Techniques

...................................................................................................................................................28

6.3.2.......................................................................................Voltage Table and Injection Points

...................................................................................................................................................30

6.1.1........................................................Receiver DC Voltages - No Signal Input - USB Mode

...................................................................................................................................................30

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SBE SB-36 OPERATION MANUAL

1.0 INTRODUCTION

1.1 GENERAL

The SB-36 Transceiver is a single sideband, suppressed carrier, digital
read-out transceiver designed for the professional / amateur radio
operator.
The SB-36 is capable of operation in the SSB and CW modes of
operation. Frequency coverage includes all amateur bands between 3.0
and 29.7 MHz.
Provisions are made for spare crystals permitting operation in the non­amateur frequencies from 4-7 or 8-14 MHz. Tuning to the precise
frequency of operation is accomplished by observing the Arabic
numerals being indicated by the nixie tubes while adjusting the VFO
control for the desired display.
Included as standard equipment in the SB-36 are VOX, ANTI-VOX,
Noise Blanker, and Break-In CW.
The SB-36 consists of a basic transceiver unit and accessory AC Power
Supply. The companion AC Power Supply will operate from 117 VAC or
220 VAC, 50/60 Hertz.
The unique digital read-out incorporated in the SB-36 allows direct,
accurate, instantaneous frequency read-out to within ±100 Hz. This
accuracy will provide more reliable communications for the serious
amateur.

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SBE SB-36 OPERATION MANUAL

1.2 SPECIFICATIONS

1.2.1 General

Frequency Range

3.50 - 4.00 MHz
7.00 - 7.50 MHz

14.00 - 14.50 MHz

21.00 - 21.50 MHz

28.00 - 30.00 MHz

Frequency Accuracy Nixie tube Read-out, accurate to within +100 Hertz

on all bands

Dimensions Transceiver: 13 - 1/4 inches wide

7-1/4 inches high
l2-1/2 inches deep
Power Supply: 6 inches wide
7-1/4 inches high
l2-1/2 inches deep

Weight Transceiver:29 pounds

Power Supply: 15-1/2 pounds

1.2.2 Transmitter

Power Input SSB 500 watts, P.E.P.

CW 400 watts
Primary Input Voltage 115/220 VAC, 50/60 Hertz
PA cooling Fan Built. in to PA compartment
Carrier Suppression -50 db
Distortion Products -30 db
Modes of Operation USB,LSB or CW. Selectable frown front panel on

all frequencies.
Unwanted Sideband -50 db, @ 1kHz
Antenna impedance 50-100 ohms unbalanced
VSWR Not to exceed 2:1
Audio Band Width 300-2700 Hertz @ 6 db
Sideband Rejection Filters Crystal lattice, 9 MHz
Power Conscription Single Tone Output - 550 watts
Front Panel Meter Indicates Plate current (Ip), Relative RF Output

and ALC

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SBE SB-36 OPERATION MANUAL

1.2.3 Receiver

Sensitivity 0. 5 microvolts for 10 db S+N/N
Selectivity 2.4 kHz @6 db

4.2 kHz @60 db
Spurious Response Image and IF responses down at least 50 db
Stability 100 Hertz (or less) per 1/z hour under any normal

ambient condition
Audio Output 2. 5 watts @ 10% distortion
Speaker 8 ohms, built into accessory AC Power Supply

unit. Rear panel jack provided for external

speaker.
Noise Blanker IF type, switchable from front panel.
Receiver Incremental Tuning

(RIT)

±7 kHz, nominal

Power Consumption 100 watts
Front Panel Meter Calibrated in "S" units
Ear Phones Jack on front panel. 600 ohm output.

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SBE SB-36 OPERATION MANUAL

2.0 INSTALLATION

2.1 GENERAL

The SB-36 Transceiver is designed for Fixed, portable or mobile
operation. No special precautions need be observed in choice of a
location, provided adequate ventilation is available. A minimum of two
inches air space above the top cabinet and on all sides is
recommended to allow proper air flow around the top and bottom of the
cabinet. Do not place the unit on a car seat or similar surface which
knight block air flow through the bottom. Never stack other units above
or below the cabinet since the accumulated heat could cause
permanent damage.

2.2 FIXED STATION

Connect the transceiver's power supply inter-connect cable, speaker
cord and plug the 117 VAC power cord into an AC outlet to provide
power to all circuits for AC operation. The transceiver should be
connected to a good water pipe ground. The ground should be
connected to the terminal provided on the rear panel of the transceiver.

2.3 ANTENNAS

Results in both receiving and transmitting are dependent largely on the
antenna. The receiver is particularly sensitive to the antenna used. Any
of the common antenna systems designed for use on the higher
frequency amateur bands may be used with the SB-36 provided the
input impedance of the antenna system matches the capability of the pi
output matching network (50-100 ohms resistive). If a tuned open-wired
transmission line is used, or if a long wire antenna is desired, a suitable
antenna tuner must be used between the transceiver and the
transmission line to provide an impedance match between the
unbalanced pi output network and the balanced open wire line or long
wire.

2.4 LINEAR AMPLIFIER

Any conventional linear amplifier requiring 300 watts of drive or less
may be used in conjunction with the SB-36. An external jack on the rear
panel provides relay control information to accessory linear amplifiers.
Another external jack on the rear of the transceiver will accept ALC

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SBE SB-36 OPERATION MANUAL

feed-back information from the linear amplifier to control the power
output of the transceiver.

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SBE SB-36 OPERATION MANUAL

3.0 OPERATION

3.1 OPERATING INSTRUCTIONS

3.1.1

The front and rear panel controls, connectors and indicators used in
operating the SB-36 are shown in Figures 3.1 and 3.2 and are
described in Table 3.1. The descriptions given in the table are not
intended to be operating instructions, but only a reference to determine
the function of each stern. The actual transceiver operating procedures
will be covered in Sections 4.1 through 4.3.

FIGURE 3.1 SB-36 FRONT VIEW

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3.1 OPERATING INSTRUCTIONS

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SBE SB-36 OPERATION MANUAL

Number Nomenclature Description
1 RIT Push- On Switch The receiver incremental (RIT) is activated by depressing

the PUSH-ON switch.

2 RIT Lamp Wren the RIT PUSH-ON control is activated, the RIT Lamp

will be lit.

3 RIT Control Potentiometer varies the frequency of the VFO Oscillator, +7

kHz in the receive mode.

4 MIC Gain Control A dual function potentiometer. In USB or LSB modes of

operation, the microphone gain regulates the level
of audio input from the transceiver microphone. When the
mode switch is in the TUNE position, the MIC Gain Control
adjusts the RF drive to the final amplifier to a suitable level
for tuning the transmitter.

5 Noise Blanker

OFF/ON Switch

A two-position switch which controls the receiver noise
blanker. Noise blanker does not function when the
control is set to "OFF”. In the "ON" position the noise
blanker will cancel RF noise pulses in the receiver.

6 "kHz" Display A six nixie tube numeric read-out display is present

whenever the transceiver is activated.

7 Upper Band Limit Light This light will be activated on the following bands whenever

the VFO tuning knob is rotated beyond the
upper edge of the band: Bands effected:

3.5 - 4.0 MHz

28.5 - 29.0 MHz

29.5 - 30.0 MHz
The upper band limit light will not be activated on the
remaining bands.

8 Lower Band Light This light will activate whenever the VFO frequency knob is

turned below the lower limit of the band selected by the
band selector knob.

9



Meter The meter indication is dependent upon which "METER"

switch position is selected. When receiving, the 0-60
scale indicates receive signal strange regardless of the
"METER” switch position. In the IP position the 0-800
milliamp indication on the meter scale should be used. In the
ALC position, the bottom portion of the scale marked ALC
should be used.

10 AGC Switch A 3-position slide switch that determines the operation of the

autocratic gain control (AGC) circuit used in the receive
more. The OFF position opens the AGC output signal path
and the remaining two positions complete
the signal path. The "FAST" position selects a fast time
constant AGC voltage decay and the "SLOW" position
selects a slow "HANG" time constant AGC voltage decay.

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SBE SB-36 OPERATION MANUAL

11 Meter Switching The "METER" switch is used to select the desired parameter

to be measured. The three functions of the switch are as
follows;

ALC: When transmitting, place the meter switch in the

ALC position. This will help in determining the
proper levels of microphone gain and ALC.

IP: In this position, the meter will indicate plate current

in the final amplifier tubes.

RF: In this position, the meter will indicate the relative

RF output power of the transceiver.

"S” Meter: When receiving, the front panel meter indicates
the signal strength of the incoming receive signal
irregardless of the position of the meter switch.

12 Plate control The Plate Tuning Capacitor resonates the final amplifier Pi-

network capacity by varying the input capacity of the Pi­network.

13 Load control The Load Control matches the output impedance of the Pi-

network
to the impedance of the load.

14 PHONES Connector The jack connector that permits low impedance head- phone

connection. When the head-phone plug is inserted, the
speaker is disconnected from the circuit.

15 MIC connector The jack connector that permits a low-medium impedance

microphone audio output and push-to-talk lines to be
connected to the transceiver.

16 Mode Switch P. OFF: Main power removed from the transceiver.

TUNE: Tune position is used for transmitter tune-up (USB

selected).
USB: For upper sideband operation.
LSB: For lower sideband operation
CW: For CW operation.

17 "RF" Gain control A potentiometer which varies the operating bias of the first

receiver RF amplifier.

18 "AF" Gain Control The potentiometer which is used to set the speaker or

headphone audio output to a comfortable listening level.

19 VFO Tuning Knob A control that permits tuning of the VFO. Its movement

covers a 500 kHz band spread range with approximately
30 kHz per revolution. The exact position in the band, to
within +100 Hertz is indicated in the Nixie-tube
display.

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SBE SB-36 OPERATION MANUAL

20 100 Hz ON/OFF

Switch

A two-position switch which controls the 100 Hertz Nixie
tube. In the. ON position, the 100 Hertz Nixie tube
will be lit. In the OFF position the 100 Hertz Nixie tube will
be turned off.

21 "MHz" Band Selector An 11-position rotary switch used to select the desired

frequency band. The "A", "B" or "C" positions will result in no
transmitter output unless optional crystals have been
installed for non-amateur band use. The remaining positions
represent the specific low-end frequency of
the selected band.
WARNING: Do not change position of the "MHz" band
selector when the SB-36 is keyed for transmit condition,
as this will result in damage to the equipment, which is not
covered by the warranty.

22 Pre-Selector Control A control used to tune both the receiver RF front end and

the transmitter mixer and driver plate circuits.

23 VOX, REC-PTT, Send

Switch

A 3-position snap switch which provides for the following
functions:
In the VOX position, the built-in VOX circuitry in the unit is
activated.
In the REC-PTT position, the receiver will function until the
PUSH-TO-TALK button on the microphone is depressed to
activate the transmitter. When placed in the SEND position,
the transmitter is automatically keyed. This position should
be used for transmitter tune-up.

24 CARR Control A potentiometer that varies the level of carrier re-insert. This

control will adjust the transmitter power output when the unit
is in the CW mode of operation.

25 ALC Control A potentiometer that varies the gain of low level transmit

stages in the transceiver to prevent fiat-topping or over
driving the final amplifier tubes.

26 BIAS Control A potentiometer that varies the grid voltage to the final

amplifier tubes. This control should be used to set the final
amplifier plate current at 50 milliamps idle current.

27 External VFO Jack A connector for applying the output of an external VFO to

the transceiver.

28 KEY Jack A connector for applying the output of an external paddle

key.

29 VOX- SENSE Control A potentiometer that varies the attenuation of the audio input

being applied to the VOX amplifier circuitry. Its function is to
adjust the threshold level of speech that is required to key
the transmitter.

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SBE SB-36 OPERATION MANUAL

30 DELAY Control Potentiometer that varies the resistance in a time constant

circuit on the audio board. When using VOX keying in the
transmit mode, its function is to adjust the length of time that
the transmitter stays keyed after the operator stops
speaking.

31 ANTI- TRIP Control The potentiometer that varies the attenuation of the speaker

audio signal being applied to the ANTI-VOX amplifier circuit
input. Its function is to adjust the threshold level of the
modulated audio that keeps the SB-36 keyed for a receive
condition.

32 Phone Patch

"IN JACK"

A connector which will accept phone patch information to
excite the transmitter.

33 Phone Patch

"OUT JACK"

A connector which provides a 600 ohm audio output for use
with phone patch devices.

34 Antenna Jack The SO-239 connector for connecting the antenna to both

transmitter output and receiver input.

35 VFO Jack A 7-pin socket to be used in conjunction with the external

VFO accessory. When the external VFO is not used, the
dummy VFO plug should be installed in this
socket.

36 Ext. ALC Jack A connector for accepting external ALC information from a

companion linear amplifier to control the transmitter output.

37 RF Jack This jack provides a low-level output for use with a

transverter.

38 REM Jack This jack provides a remote output to control a companion

linear amplifier. The remote output jack
provides a ground connection when the transceiver is in the
transmit mode.

39 SP Jack A connector providing an audio output for external speaker

use.

40 POWER connector An 11-pin plug providing primary and secondary power input

connections from the accessory power supply.

41 GROUND Connector A threaded bolt with wing nut provided for earth ground

connections.

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SBE SB-36 OPERATION MANUAL

4.0 OPERATING PROCEDURE

WARNING:

Under no circumstances should operation of the SB-36 be attempted without a
proper antenna or dummy load of specific power handling capability. Please
read Sections 4.1 through 4.3 fully before attempting to operate the SB-36
Transceiver.

4.1 RECEIVER OPERATION

4.1.1 Rotate the mode selector switch clockwise from the P. OFF position to the
desired operating mode. Allow approximately two minutes for warm-up.

4.1.2 Rotate the BAND selector switch to the desired band.

4.1.3 Advance the RF gain control to the full clockwise position.

4.1.4 Rotate the AF Gain Control to its mid-range position.

4.1.5 Rotate the VFO Tuning Knob to the desired operating frequency.

4.1.6 Adjust the PRE-SELECT control until maximum back ground noise/interning
signal is obtained.

4.1.7 Place the noise blanker and AGC controls in desired operating position.

4.1.8 Adjust the RF and AF Gain Controls for a suitable listening level.

4.1.9 Fine tuning of the incoming signal may be accomplished by either rotating the
main VFO tuning knob or by use of the RIT control.
NOTE: If the RIT control is used, the Nixie tube read-out will indicate the exact
frequency of the incoming signal. When the SB-36 is placed in the transmit
mode, the Nixie tube read-out will revert back to the frequency selected when
the RIT control was off.

4. 2 TRANSMIT TUNING PROCEDURE

4.2.1 For transmitter tune up, place the controls as outlined in Steps 4.1.1 through

4.1.9.

4.2.2 Position the plate tuning control to correspond to the band on which operation
is desired.

4.2.3 Rotate the LOAD control to its maximum counter clockwise position.

4.2.4 Place the meter switch in the IP position.

4.2.5 Rotate the MIC control to its maximum counter clockwise position.

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SBE SB-36 OPERATION MANUAL

4.2.6 Place the MODE switch to the TUNE position.

4.2.7 Place the VOX/REC-PTT/SEND switch to the SEND position.

4.2.8 Advance the MIG Gain Control slightly while tuning the PRESELECT control for
maximum indication on the meter.
CAUTION: Do not exceed 300-400 mA of plate current until final amplifier
tuning and load control have been properly adjusted.

4.2.9 Rotate the PLATE tuning control for minimum or dip indication on
the IP reading. When dip is obtained, advance the MIC Gain Control
to produce a 300-400 mA indication on the meter.

4.2.10 Place the METER switch in the RF position.

4.2.11 Rotate the LOAD control for maximum meter indication. Use the MIC Gain
Control as necessary to keep the maximum meter indication below 600-700
mA indication on the meter. Tune both the PLATE Tuning Control and LOAD
control to obtain Maximum indication on the meter.

4.2.12 Place the VOX/REC-PTT /SEND switch to the REC-PTT position. Rotate the
MODE switch to either Upper or Lower Sideband position.

4.2.13 Place the METER switch in the IP position. Press the push-to-talk button on the
microphone and, while speaking into the microphone in a normal tone of voice,
adjust the microphone gain control for an average IP indication of 350-400
milliamps.

4.2.14 Place the METER switch in the ALC position. The meter will indicate nearly full
scale deflection. Adjust the ALC potentiometer (located on the rear panel of the
radio) so that on voice peaks, a slightly downward indication is obtained on the
meter. This will indicate that the ALC is functioning properly.

4.2.15 The METER switch may now be placed in the RF position to indicate relative
transmitter power output.

4. 3 CW OPERATION

4.3.1 Perform the steps outlined in sterns 4.2.1 through 4.2.15.

4.3.2 Place the VOX/REC-PTT/SEND switch to the VOX position.

4.3.3 Rotate the MODE switch to the CW position.

4.3.4 Connect a key to the KEY jack located on the rear panel of the
transceiver.

4.3.5 Depress the key and adjust the VOX SENSE CONTROL on the rear
panel so that the transmitter keys on. It may be also necessary to adjust the
ANTI-VOX potentiometer on the rear panel of the unit.

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SBE SB-36 OPERATION MANUAL

4.3.6 With the key depressed, adjust the CARR potentiometer (located on the rear
panel of the unit) so the transmitter power output does not exceed 200 watts on
15 through 80 meters or 150 watts on 10 meters.

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SBE SB-36 OPERATION MANUAL

5. 0 THEORY OF OPERATION

5. 1 GENERAL

5.1.1

Figure 5.1 shows the basic transmitter receive signal paths and the
printed circuit boards associated with each. The SB-36 Transceiver is
comprised of a power amplifier assembly, accessory power supply, and
one each of the following circuit boards:

Drive RF/Pre-Mixer and Oscillator Board, Counter Unit, VFO Oscillator,
carrier Oscillator Board, Double Sideband Amplifier/Crystal Filter/Noise
Blanker Board, Microphone Amplifier and Side Tone Oscillator Board,
Receiver IF Amplifier and AGC Amplifier Board, 20 volt Regulator
Board, AF Power Amplifier Board, and VOX and ANTI-TRIP Board.

The printed circuit board relationship in respect to transmit or receive
signal paths is shown in Figure 5.1. In the transmit mode, the signal is
routed from the microphone through the MIC AMP Board, Double
Sideband AMP/Crystal Filter Board, Driver RF/Pre-Mix and Oscillator
Board, and PA Assembly. A more detailed explanation of the transmit
signal path is covered in paragraph 5.2. In the receive mode the signal
is routed from the antenna connector through the PA assembly, Driver
RF/Pre-Mix and Oscillator Board, Double Sideband Amplifier / Crystal
Filter Board, Receiver IF Amplifier and AGC Amplifier Board, Audio PC
Board, to the external speaker jack. A more detailed explanation of the
receiver signal path is covered in paragraph 5. 3.

Frequencies generated by the BFO (9 MHz) Board are routed to the
double sideband amplifier and noise blanker board and from there are
routed to the driver RF/Pre-Mixer and Oscillator Board. Frequencies
generated by the VFO are routed to the Driver RF/Pre-Mixer and
Oscillator Board. The Theory of Operation section employs the use of
more detailed block diagram's than Figure 5.1. Complete schematics
are also contained in Section 7 and should be used in conjunction with
the description of the transmitter and receiver circuitry contained in the
following paragraphs.

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SBE SB-36 OPERATION MANUAL

5. 2 TRANSMITTER CIRCUITRY

5.2.1 Transmitter Signal Path

Stage-by-Stage transmit signal path block diagrams is shown in Figure

5.1. Unless otherwise indicated in the following explanation, it is
assumed that the SB-36 is operating in the Single Sideband Mode.

Audio signals from the microphone connector or phone patch input jack
are routed to TR-l located on the Microphone Amplifier and Side Tone
Oscillator Board. The audio signal is amplified by transistor TR-l and
then routed to the base of TR-2. The amplified output of transistor TR-2
is routed through transistor TR-3, which is operating as an emitter
follower. The output of transistor TR-3 is routed through variable
resister VR-l (Microphone Gain Potentiometer) to the base of transistor
TR-4.

The signal from transistor TR-4 is then routed to one input of the
balanced modulator. The balanced modulator is comprised of
transformer T-9 and Diodes D-1 through D-4. The second input of the
balanced modulator is a 9.0 MHz carrier signal. The 9.0 MHz carrier
signal originates in the carrier oscillator board and is applied to the
balanced modulator by variable resistor VR-5. The balanced modulator
mixes the 9.0 MHz carrier with the audio signal to produce a resultant

9.0 MHz double sideband signal with a carrier suppressed
approximately 40 dB. Third and higher order modulation products are
also suppressed approximately 30 dB below each sideband. The
balanced modulator output is routed to the input of the upper or lower
sideband crystal filter.

The output from the crystal filter is routed by transformer T-10 to the
input of transistor TR-7. The output of transistor TR-7 is coupled by
transformer T-11 to the grid of mixer tube V-1.

A second input to the grid of mixer tube V-l is derived by mixing the
output of the HFO transistor TR-10 with the output of VFO oscillator.
The HFO oscillator output and the VFO oscillator output are combined
in mixer transistor TR-11. The resultant frequency is transformer
coupled to the grid of mixer tube V-1.

The desired transmit frequency is obtained by mixing the 9.0 MHz
sideband output of transistor TR-7 with the HFO/VFO product produced

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SBE SB-36 OPERATION MANUAL

by transistor TR-11. The output of mixer tube V-l is coupled to the grid
of V-2, the driver tube. Output of tube V-2 is capacitively coupled to the
input of the PA tubes, V-5 and V-6.
Normal signal level at the PA tube input is 50 volts peak-to-peak. The
signal passes through the plate tuning circuits and metering circuits to
the main antenna connector located on the rear panel.
The RF power output at the connector is a nominal 300 watts on 15-80
meters and 200 watts on 10 meters.

5.2.2 Automatic Level Control

Automatic Level Control (ALC) is employed to control the amount of RF
drive to the power amplifier tubes. The ALC method utilized by the SB­36 is shown in simplified diagrams Figure 5.2. When the signal present
on the grid of the final amplifier tubes exceeds the grid bias of the tube,
Diodes D-29 and D-30 conduct.
This conduction will establish a reference voltage across the ALC
potentiometer.

The voltage on the center terminal of the ALC potentiometer is fed back
to the gate of transistor TR-7. This voltage is used to control the gain of
TR-7 to prevent flat-topping of the transmitter signal. This system of
ALC allows a high average level of modulation without a corresponding
increase in distortion products.

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SBE SB-36 OPERATION MANUAL

5. 3 RECEIVER CIRCUITRY

5.3.1 Receiver Signal Path

RF signals from the antenna connector pass through the antenna relay
and trap coil L-24 to the grid of 1st, the first RF amplifier. Trap Coil L-24
minimizes spurious receiver response caused by signals which fall
within the 9 MHz IF frequency range. The amplified signal from V-4 is
coupled to the grid of V-3, the receiver mixer tube. Signals present in V­3 consist of the incoming RF signal and the VFO/HFO mixture from TR-

11.

The output of V-3 is a 9 MHz IF signal which is coupled to either the
upper or lower crystal filter through transformer T-9A. Output of the
crystal filter is then coupled to TR-7, TR-28, TR-27 and TR-i6 which are
all 9 MHz IF amplifiers. The output of TR-26 is coupled to both the
receiver balance protector circuit and the receiver AGG circuit.

The 9 MHz output of the TR-26 is also coupled to Diodes D-18 through
D-21, the receiver balanced detector. The audio output of the balanced
detector is then applied to VR-509, the AF gain control. The audio
signal front the wiper of VR-9 is routed to the audio printed circuit board
where it is coupled to the base of TR-25. The output cf TR-25 drives
TR-22 and TR-23 the AF power amplifier transistors.

The resultant audio output from TR-22 and TR-23 is applied to the
earphone jack, speaker jack and telephone patch out jack.

5.3.2 Noise Blanker

The noise blanker circuit utilized in the SB-36 Transceiver receives
noise information directly from the antenna connector. The incoming
noise signal is amplified by integrated circuit TR-8 detected by Diodes
D-205 and D-206 and coupled to the gate of TR-7 to inhibit the received
signal from passing through
TR-7 during the presence of strong RF noise pulses.

5.3.3 Automatic Gain Control

Automatic Gain Control (AGC) is employed in the SB-36 Transceiver to
maintain a constant receive signal level passing through the front end
and IF Amplifier Board. The AGC circuitry can be completely disabled
by switching the front panel "AGC" control to the "OFF" position.

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