Conar 280 Manual

Operating and Maintenance
Instructions for the
CONAR
Signal Generator
Model 280
Price $1.00
QUALITY EQUIPMENT BUILT ON A HALF CENTURY OF SERVICE IN ELECTRONICS

CONAR
Model 280 Signal Generator
Operating and Maintenance Instructions
SPECIFICATIONS
OutputAmplitude:
BandsA, B, and C:
at least 1 volt peak to peak.
Bands D, E, and F:
at least 20,000 microvolts.
Audio:
at least 5 volts peak to peak.
RF and Modulated RF continuously
variable within six bands.
BandA170 kc to 550 kc
Band B 550 kc to 1600 kc
Band C 1.6 mc to 5.0 mc
Band D 4.5 mc to 15 mc
Band E 15 mc to 30 mc
Band F 30 mc to 60 mc
7-l/2" high x 9-7/8" wide x 6-1/2" deep
9 lbs (shipping weight)
115 volts, 60 cyclesAC, 10 watts
(1) 6BE6, (1) 12AU7
Power Transformer and Selenium rectifier.
RF; 170 KC to 60 MC,
RF Modulated; 170 KC to 60 MC by 400 cps,
Audio; 400 cps audio signal
Cabinet Size:
Weight:
Power Requirements:
Tube Complement:
Power Supply:
Output:
Accuracy: Better than 3% after calibration.
Attenuator: Course: High-Low switch.
Fine: Continuously variable potentiometer.
Output Cable: Permanently attached,
low loss coaxial, terminated in alligator clips.

Operating Instructions:
DESCRIPTION OF CONTROLS
Function Switch:
Band Switch:
Tuning Control:
Attenuator Control:
High-Low Switch:
Output Cable:
HOW TO READ THE SCALES:
The CONAR Model 280 Signal Generator is easy to
operate. The front panel labels for the controls and
scales enable you to set up the instrument for the
output signal you desire. The following discussion of
the controls, the scales, and the circuit is included to
help you become thoroughly familiar with the
instrument.
The operating controls of your CONAR Signal
Generator are conveniently grouped for easy
operation. Let's consider the function of each control
as it relates to the operation of the instrument.
This three-position switch, marked MOD, RF, and
AUD is used to select the type of output that you get
from the instrument. in the AUD position, the output
is a 400-cycle sine wave used for testing audio
equipment. In the RF position, the output is an
unmodulated RF signal at the frequency determined
by the band switch and tuning control, in the MOD
position, the output is an RF signal amplitude
modulated by the 400-cycle audio signal.
This six-position switch is used to select the band of
frequencies produced by the generator. Each position
is marked to correspond with one of the six scales on
the dial. The bands cover the following frequencies:
BandA170 kc to 550 kc
Band B 550 kc to 1600 kc
Band C 1.6 mc to 5.0 mc
Band D 4.5 mc to 15 mc
BandE15mcto30mc
Band F 30 mc to 60 mc
*1600 kc and 1.6 mc are the same frequency.
The tuning control moves the pointer across the dial
and adjusts the frequency of the generator within the
band of frequencies selected by the band switch, The
control has a vernier type drive so you can easily make
accurate settings of the output frequency.
This is a continuously variable potentiometer used
for adjusting the size of the output signal. An "ON-
OFF" switch is ganged to this control. In the extreme
counter-clockwise position, the switch is "OFF" and
the instrument is de-energized. As you rotate the
control clockwise from the OFF position, you will
hear a slight click. This turns the instrument ON. As
the control is turned further clockwise, the signal
generator output increases.
This is a coarse attenuator for varying the signal
generator output over a wide range. The HIGH
position is mainly used when testing a receiver or
when you want a very large signal to drive through a
defective or badly misaligned stage. The LOW
position is normally used in alignment work because
you need to keep the output signal at a LOW level.
The attenuator control is then used to further attenuate
the signal to the desired level.
Acoaxial cable comes through the center of the front
panel under the tuning control; The cable is
permanently attached to the attenuator circuit so that
the cable cannot be misplaced. The shielding of the
cable confines the output signal to the center
conductor of the cable. This enables you to inject the
signal where you want it in the receiver and prevents
unwanted signal radiation,
The tuning dial has six scales, labeled at each end
with letters corresponding to the positions of the band
switch. Each scale covers a given band of frequencies.
For example, when the band switch is set at positionA,
readings are made on scale A of the tuning dial. Note
that the scales A and B are marked in kilocycles
(thousands of cycles), while the other scales (C, D, E,
F) are marked in megacycles (millions of cycles). It is
easy to convert the frequency from megacycles to
kilocycles. All that needs to be done is to move the
decimal point three places to the right. For example,
1.6-mc is 1600-kc; 1.8-mc is 1800kc, etc.
As an aid in selecting the correct setting of the band
switch, the lowest and highest frequencies covered by
each band are indicated at the extreme ends of each
corresponding scale on the tuning dial. Example:
Beneath the left end of Scale A is printed 170-kc.
Beneath the right end of Scale A is printed 550-kc.
Therefore, if any frequency between 170-kc and 550-
kc is desired, the band switch is set to position A. The
tuning control is then turned so that the red "hairline"
on the plastic pointer is directly over the desired
frequency on scaleA.
Where a number representing the desired frequency
is directly marked on the dial, the transparent pointer

is moved over the dial until the hairline is directly over
the long marker line representing that frequency.
If the signal generator is to be set to a frequency not
directly labeled on a given scale, then the short lines
between the longer marker lines are used. For
intermediate readings, an estimation is made between
the short lines. The values represented by each
division (short line) between calibrated or marked
lines for the different bands are given below:
BandA, each division represents 10-kc.
Band B, between 550-kc and800kc, each division
represents 10-kc.
Between 800-kc and 1600-kc, each division
represents 20-kc.
Band C, each division represents .05-mc or 50-kc.
Band D, each division represents .1-mc or 100-kc.
Band E, each division represents .1-mc or 100-kc.
Band F, each division represents .2-mc or 200-kc.
Let's take an example of selecting a desired
frequency. Suppose you want the signal generator to
produce a frequency of 1430 kc, Referring to the main
dial scale, we see the minimum frequency covered by
band B is 550 kc and the maximum frequency is 1600
kc. Since the frequency we want falls between these
limits, the band switch is set at position B which
covers the standard AM broadcast band of
frequencies. Next we find the line marked 1400 kc on
the B band. The next higher marked line is 1600 kc.
Halfway between 1400 and 1600 we find a long line.
We know this line is 1500 kc because It is halfway
between 1400 and 1600. The short graduations
between 1400 and 1500 mark off five spaces. Each
space must represent 20 kc because the five spaces
cover the 100 kc from 1400 to 1500. Therefore, the
first graduation above 1400 kc is 1420 kc and the
second graduation is 1440 kc. Since we want the 1430
kc, we move the hairline of the pointer halfway
between the first and second graduation above 1400
kc. The signal generator is now set to produce 1430 kc.
When setting this plastic pointer to a given
frequency, be sure that you are looking directly
toward the pointer and dial scale. If your eyes are not
squarely in front of the pointer, an error in reading the
scale, (called parallax error) will result. Be especially
careful when placing the signal generator at one side
of the receiver under test. There is a tendency to read
the dial from an angle.
The CONAR Model 280 Signal Generator uses
simple, reliable circuitry to produce an RF, modulated
RF, or audio output. The RF signals are generated In
six bands by switching different coil and capacitor
combinations to the oscillator tube. Within each band,
the frequency is continuously variable by adjusting
the tuning capacitor. The dial pointer is attached to the
tuning capacitor to indicate the exact frequency
within the band. The RF signal from the oscillator is
coupled to a cathode follower output stage. The
output signal then passes through an adjustable
attenuator to the output cable.
The modulated RF output is produced by
modulating the RF signal In the oscillator stage. A
400-cps (approximately) audio signal is applied to the
mixer grid of the RF oscillator stage to amplitude
modulate the selected RF signal. The modulated RF
signal is coupled to the cathode follower in the same
way as the RF signal.
A fixed frequency (approximately 400 cps) audio
signal is generated by an audio oscillator stage. When
the audio output is selected, the signal is applied to the
cathode follower, passes through the attenuator
circuit, and appears at the output of the output cable.
As previously described, the audio signal is also used
internally to modulate the RF signal when the
modulated RF output is selected.
The circuit of the Model 280 is shown in Fig. 1. The
Hartley type oscillator circuit was selected for its
stability. Six separate coils and capacitors form the
oscillator tank circuits. A different tank circuit is
switched to the oscillator tube for each of the six
bands of frequencies. The band switch, S1, shorts out
all the coils except the coil for the selected band. A
ganged variable tuning capacitor varies the frequency
over the selected band. The tuning capacitor, C7, has
two sections, one section for the four low bands and
one section for the two highest bands. This
arrangement assures a favorable L-C ratio for the
oscillator circuits over all the frequency bands.
The RF oscillator tube, V1, is a 6BE6 pentagrid
converter tube. This tube functions as an electron
coupled oscillator. The cathode, the first control grid
(pin 1), and the screen grid (pin 6) act as a triode to
operate the RF oscillator, The electrons that pass
through the grids and reach the plate are the electron
coupled output from the oscillator, in this way the
load placed on the output of the oscillator does not
Avoid Parallax Error:
CIRCUIT DESCRIPTION

affect the frequency of oscillation. Grid 3 (pin 7) is
used to amplitude modulate the oscillator frequency.
A 400-cycle signal is applied to this grid when the
function switch is set to the modulated RF position.
The oscillator output from the plate of V1 is coupled
through C9 to the grid of the cathode follower. The 1-
2-3 section of the 12AU7, V2, forms the cathode
follower output of the signal generator. The use of a
cathode follower provides a low impedance output
from the signal generator and acts as an additional
guard to prevent the output load from affecting the
frequency of the oscillator.
The 6-7-8 section of V2 and the associated
components form a Colpitts type audio oscillator. L7,
C12, and C13 are the frequency determining elements
of the circuit. The oscillator produces a sine wave at a
frequency of approximately 400 cps. In the
modulated RF position, this signal is fed through R6,
C14, and S3 to grid 3 (pin 7) of the oscillator tube. In
the audio position, the 400-cycle signal is fed to the
grid of the cathode follower. Notice that In the audio
position, B+ is removed from the plate and screen of
V1 so there is no RF output.
The output from the cathode follower is fed to the
output cable through an attenuator network. The 3K
potentiometer, R11, provides a continuous variation
of the output, High-Low switch, S4, provides a large
step-change In the output signal, Both the High and
the Low output are continuously variable, The output
from the attenuator network is coupled through C17
to the output cable. This capacitor isolates the signal
generator circuitry from the receiver you are working
on. Thus it is safe to inject a signal to the plate of a tube
in a receiver even though the plate has B+ voltage on it.
The output cable is a low capacitance coaxial cable.
The grounded coaxial shield prevents signal radiation
from points other than the output clip on the end of the
cable.
The power transformer provides isolation of the
instrument from the power line. The voltage from the
high-voltage secondary on the transformer is rectified
and filtered to provide B+ for the instrument. The
low-voltage secondary provides filament voltage for
the tubes.
Your CONAR Signal Generator can be used for
testing and aligning AM and FM radio receivers. The
400 cycle output is a convenient test signal for use on
all types of audio equipment.
If you have never done any alignment work you will
want to try out the instrument before you use it to
repair or align a defective receiver. The section on
alignment in this manual is to be used only as a
general guide. When aligning a specific receiver we
recommend that you follow the manufacturer's
instructions,
Skill in aligning all types of receivers takes practice
and experience. One of the best ways to start getting
this experience is to practice alignment on receivers
that are already properly aligned. Set up the
equipment and follow the alignment steps without
making any adjustment to the receiver. This will give
you practice injecting signals and observing
indications. Next, you can move adjustments In the
receiver and observe the effect. This will give you a
feel of how the adjustments should respond. Mark the
position of the adjustment before you move It so you
can put it back in case you are on the wrong
adjustment. Most inexpensive AC-DC radios are
slightly out of alignment even when new. Realigning
several of these sets can give you valuable experience
in using your instrument.
Alignment is the process of adjusting tuned circuits
to respond to a desired frequency or band of
frequencies. In a superheterodyne radio receiver, the
tuned circuits consist of the RF stages, the IF stages,
and the local oscillator circuit. The RF stages are
aligned to produce maximum response to the band of
frequencies covered by the particular receiver. The
local oscillator must be adjusted so it will "track".
That is, the local oscillator must produce the correct
frequency at all settings of the radio tuning dial. The
correct frequency is the frequency that when mixed
with the incoming signal from the desired radio
station produces a fixed intermediate frequency. The
IF stages are adjusted to give maximum response to
the intermediate frequency (usually 455 kc).
To align tuned circuits, It is necessary to have a
signal source and a response indicator. Your signal
generator provides the signal source at the frequency
that the tuned circuit is to be aligned. You can use any
one of several methods to indicate the response of the
tuned circuit to the applied signal. The simplest
method is to use the speaker of the receiver. The signal
How to Align Radio Receivers
with the Signal Generator
RECEIVER ALIGNMENT
--GENERAL

from the signal generator must be modulated to
produce an audible tone from the speaker. Then as the
circuits are aligned, you judge the response by the
loudness of the tone from the speaker, Since it is
difficult for the ear to detect small changes In
loudness, other methods are considered more
accurate. However, using the speaker as a response
indicator is entirely satisfactory for aligning radio
receivers.
Another method of indicating the response of the
tuned circuits in a receiver is to connect a scope or AC
voltmeter across the voice coil of the receiver speaker.
This gives you a visual indication of the response as
you adjust the tuned circuits.
Another popular method of indicating the response
is to connect a DC voltmeter to the output of the
second detector. The meter is very sensitive to small
changes in circuit response. With this method you can
use an unmodulated signal and you do not have to
listen to the tone from the loudspeaker. One
precaution: If a circuit you are aligning breaks into
oscillation, your indicating meter will show a high
false reading. It will be necessary to find and correct
the cause of oscillation (usually feedback) before you
can peak the tuned circuit. Otherwise you will have to
align the circuit slightly off resonance where
oscillation does not occur. When an oscillating
condition is suspected, use an unmodulated signal and
listen to the output. This enables you to detect an
oscillating circuit condition because the receiver will
produce squeals or motor boating noises. You can still
use your DC meter as the response indicator,
It is necessary to inject the proper amount of signal
into the tuned circuit without detuning the circuit to be
aligned. This is usually accomplished by injecting the
signal into a stage ahead of the stage being aligned.
For example, to align IF stages, the signal is applied to
the control grid of the mixer stage. The mixer tube
isolates the tuned IF stages from the signal generator
so there is no loading effect. The amplitude of the
signal is then adjusted by attenuating the signal
generator output.
Minimum coupling should be used to Inject a signal
into the RF stages or the pre-selector section of a
receiver. Placing the output clips of the signal
generator cable near the loop antenna of a receiver
will usually radiate enough signal Into the receiver. If
the receiver is badly misaligned you can start
alignment by connecting the signal generator output
directly to the antenna terminals. This will inject
enough signal to drive through even a badly
misaligned stage. When you get the set approximately
aligned, remove the clips from the antenna terminals
and radiate the signal into the set by placing the signal
generator clips close to the antenna. This prevents any
loading effect of the signal generator during final
alignment.
Accurate receiver alignment requires the use of a
minimum signal. You want the receiver to produce Its
maximum sensitivity when receiving weak radio
stations, Therefore, final alignment adjustments
should be made using a signal strength that is just
large enough to give a good indication on your
response Indicator. In a receiver using AVC, the signal
strength should be small enough so it does not
produce an effective AVC voltage. An alternate
method is to disable the AVC voltage by shorting the
AVC line to B-.
The oscillator of your CONAR Signal Generator is a
stable circuit that will show no appreciable frequency
drift during warm-up. However, it is good practice to
allow the generator to warm up for ten or fifteen
minutes before using It. The circuits in some receivers
will drift noticeably during warm-up, Therefore, turn
on the set and allow it to warm up for about fifteen
minutes before starting the alignment procedure,
When aligning the IF section of a receiver, it is
desirable to disable the local oscillator. This prevents
the local oscillator signal from beating with the signal
generator signal and producing confusing signals,
The local oscillator can be disabled by shorting the
oscillator section of the tuning capacitor.
To obtain maximum sensitivity from a radio receiver
you can use an alignment procedure known as
"rocking". This procedure may produce inaccuracies
in the dial readings of the radio, however, the dial
markings on most broadcast radio receivers are only a
rough indication of the frequency that the radio is
tuned to. Therefore, the disadvantage of small
inaccuracies in the dial settings is more than offset by
the improved receiver sensitivity.
The "rocking" alignment procedure can be used on
any receiver having a padder capacitor or a tuning
slug in the local oscillator coil. In most cases, the
Injecting the Signal:
Use Minimum Signal:
Warm-up Time:
Disabling the Local Oscillator:
Obtaining Maximum Sensitivity:

receiver will be a transistor set because most modern
tube broadcast receivers do not have a padder. In the
following discussion, the word "padder" refers to the
padder capacitor or the tuning slug in the oscillator
coil.
First, adjust the oscillator and RF trimmers for
maximum output at 1500 kc with the receiver dial set
at 1500 kc. The RF section of the receiver is now
properly aligned and should not be adjusted again.
Next, set the signal generator tuning control to 600
kc. Tune the receiver to produce maximum output
Indication regardless of dial setting. Write down the
exact dial reading.
Change the setting of the padder slightly. Retune the
receiver for maximum output, and make a note of the
output. If the output has increased, you are adjusting
the padder in the correct direction; if the output has
decreased, you are adjusting the padder in the wrong
direction.
If you are adjusting the padder in the correct
direction, continue adjusting the padder In that
direction, retuning the receiver dials until maximum
output Indication is obtained. Of course, you must
tune the padder slightly beyond the correct point
(where the output begins to decrease) and then come
back to make certain you have the maximum.
If the original padder adjustment was in the wrong
direction, turn the padder In the other direction, retune
the receiver and note the output. Continue this
procedure until maximum output is obtained, again,
you will have to tune slightly beyond the correct point
to make certain you have the maximum output.
This "rocking" adjustment increases the receiver
sensitivity at the expense of exact dial calibration by
effectively adjusting the oscillator and the pre-
selector simultaneously. The combination of setting
the padder and the receiver dial adjusts the oscillator;
setting the receiver dial adjusts the mixer and the pre-
selector.
After performing the "rocking" adjustment at the
low end of the receiver dial, you must adjust the
oscillator trimmer capacitor at the high end of the dial.
Repeat these adjustments until the dial calibration is
correct at the high end of the dial, and the padder is
adjusted for maximum response at the low end of the
dial, when you have done this, the receiver will track
reasonably well and maximum sensitivity will be
obtained over the entire tuning range.
The following alignment procedure is presented as
an example that can be used for aligning receivers
when instructions are not available, if the
manufacturers alignment data is available, it should
be used. Fig. 2 shows a typical AC-DC broadcast
receiver; Use this schematic to follow the alignment
steps.
1. Plug in and turn on both the Signal Generator and
the receiver to be aligned, Allow a few minutes for
them to warm up.
2. Connect a DC voltmeter across the volume control.
You could, of course, use one of the other response
indicators discussed previously. The volume control
in Fig. 2 is the 500K potentiometer, R5. Connect the
voltmeter to terminals 20 and 18. The high end of the
volume control will have a negative potential so set
the meter to read DC on the 3-volt scale.
3. Short the oscillator section of the tuning capacitor,
C2. This can be done by connecting a jumper from
terminal 17 to the chassis. This disables the receiver's
local oscillator and prevents spurious signals during
IF alignment.
4. Disable the AVC voltage by connecting a jumper
between terminals 2 and 3, this shorts out capacitor
C7 and grounds theAVC voltage.
5. Connect the signal generator output to the terminals
of loop L1 at the antenna. Notice that L1 is a single
turn of wire near the built-in loop antenna, L2, The
output of the signal generator will radiate a signal
from L1 into the loop antenna, L2.
6. Set the Signal Generator to produce the receiver's
intermediate frequency, In this case, 455 kc, Set the
Band switch to A, Tune the Signal Generator so the
red hairline on the plastic pointer is over 455 on scale
A. Set the function switch to RF. Adjust the
attenuator (HIGH-LOW switch and ATTENUATOR
control) to produce about 1 volt reading on the
response indicator.
7. Adjust the AC-DC trimmers for maximum reading
on the response indicator. The IF trimmers are C5, C6,
STEP BY STEP ALIGNMENT OF
A TYPICAL VACUUM TUBE
RADIO RECEIVER

CS, and C9 in Fig. 2, in many receivers, the IF
adjustments are made by moving an iron core slug in
the IF coil. As you adjust for maximum response,
keep attenuating the input signal as necessary to keep
the voltmeter reading on scale.
8. Repeat all IF adjustments starting with the second
detector adjustment (C9 In Fig, 2) to eliminate the
effects of interaction between the adjustments.
9. Remove the short across the oscillator capacitor.
10. Check the position of the dial pointer on the
receiver, A calibration point is frequently given at one
end of the dial scale to indicate the correct position of
the pointer when the tuning capacitor is completely
open or completely closed. If such a calibration point
is given, make certain it lines up with the dial pointer.
If it does not, adjust the dial pointer so it lines up with
the calibration mark.
11. Set the receiver dial to 1500 kc. If there is a local
station at 1500 kc, set the receiver dial to any
frequency between 1500 kc and 1600 kc that can be
read accurately from the receiver dial.
12. Set the Signal Generator Band switch and tuning
control to the frequency indicated by the receiver dial.
Adjust the oscillator trimmer (OT) for maximum
reading on the response indicator. The oscillator
trimmer is a screwdriver adjustment on the tuning
capacitor. C2 in Fig. 2, Also adjust the antenna
trimmer (AT) mounted on section C1 of the tuning
capacitor gang for maximum output.
13. If the receiver has an oscillator padder adjustment,
adjust the padder at 600 kc as discussed in the
preceding section under "Obtaining Maximum
Sensitivity.”
14. Remove the short circuit that you previously
placed across capacitor C7. Removing the short
circuit allows theAVC voltage to again reach the grids
of the tubes and thereby be effective. Disconnect the
response indicator and the Signal Generator from the
receiver. You now have the receiver properly aligned.
A transistor receiver is aligned in much the same
way as a tube type receiver. The IF stages are aligned
first, then the oscillator and mixer circuits. The IF
stages are slug tuned transformers. Likewise, the local
oscillator is usually tuned at the low frequency end of
the dial by adjusting a slug in a coil or a transformer.
The antenna and oscillator trimmers are adjusted at
the high frequency end of the dial. The powered iron
core in L1 is not adjustable.
When aligning transistor receivers, keep in mind the
difference in operation of tubes and transistors. Since
transistors are current operated devices, the signal
voltages are small at the transistor terminals. The
transistors have relatively low input and output
impedance. Therefore the transistors are matched into
low impedance points in the tuned circuits.
Transistors do not provide as much isolation as tubes.
A relatively small signal may be coupled through a
transistor stage even with the transistor back biased to
cut off. The low impedance points in the transistor
receiver will severely load down the output of some
signal generators. Your Model 280 Signal Generator
has a low impedance output that will provide
adequate signal for testing at any point in the
transistor receiver. However, for alignment purposes
It is usually easier to inject both the RF and IF signals
into the antenna circuit. A suitable way is to loop the
ground lead of the Signal Generator around the loop
stick of the receiver. Clip the ground lead and the hot
lead together. This arrangement prevents unwanted
signal radiation and will radiate plenty of signal into
the antenna circuit.
Atypical transistor radio receiver is shown in Fig. 3.
The first step in alignment is to connect a VTVM
between the collectors of the output transistors, Q5
and Q6. An easy place to locate these connection
points is at the leads from the primary of the output
transformer, TR5. Any of the response indicators
discussed earlier may be used but the VTVM is most
satisfactory. Since your VTVM will be indicating the
detected signal, set the VTVM to read AC on the
lowest range. Disable the local oscillator by shorting
the oscillator section of the tuning capacitor. This is
the section with the fewest plates (In some cases the
plates are smaller). Simply connect a lead from the
oscillator section terminal to the chassis.
Set up the Signal Generator to produce the IF
frequency; in this case 455 kc. Set the band switch to
BandA. Rotate the tuning knob to bring the hairline of
the plastic pointer to the 455 kc position on the scale
for Band A. Set the function switch to modulated RF.
Set the High-Low attenuator switch to Low. Rotate
the attenuator knob for maximum attenuation (low
end of markings). Loop the ground lead of the output
cable over the receiver loop stick and clip the hot and
STEP BY STEP ALIGNMENT
OF A TRANSISTOR RECEIVER

ground leads together as previously explained. Turn
on the receiver and turn the volume control to
maximum. Increase the output of the signal generator
while observing the pointer of the VTVM. Increase
the output until you can easily hear the 400 cps
modulation. You are now ready to make alignment
adjustments.
Adjust the slugs in the IF coils for maximum
response. First, adjust the slug in TR3 for maximum
Indication on the VTVM. As the VTVM reading
increases, attenuate the signal from Signal Generator.
Next, adjust the slug in TR2 for maximum response.
Attenuate the Signal Generator as necessary to keep
the VTVM reading on scale. Finally, adjust the slug in
TR1 for maximum response. Keep the generator
output as low as possible. This is important for
obtaining maximum sensitivity In this stage.
In this receiver, it is impractical to disable AVC
because this would remove the forward bias from
transistor Q2. Notice that forward bias for Q2 is
obtained by applying a negative voltage through R4
and the secondary of TR1 to the base of Q2. This
negative forward bias is opposed by a positive AVC
voltage. The AVC voltage is picked off the top of R10
and filtered by R5, C3 and C4. If C3 were shorted to
remove the AVC voltage, the forward bias would also
be shorted and the transistor would remain cut off.
Therefore, TR1 should be adjusted while applying a
very small IF signal which produces very little AVC
voltage. This completes the alignment of the IF
section of the receiver.
Next adjust the local oscillator and pre-selector
short from the oscillator section of the tuning
capacitor. Set the Signal Generator band switch to
band B and move the pointer to 600 kc. Tune the
receiver so the dial indicates 600 kc. Now adjust the
slug in L4 to get a maximum indication on the VTVM.
Attenuate the signal from the Signal Generator as
necessary to keep the VTVM pointer on scale. Move
the pointer on the Signal Generator to 1500 kc. Tune
the receiver to 1500 kc. Adjust the oscillator trimmer
for maximum indication on the VTVM.Adjust the RF
trimmer capacitor for maximum output. The RF
trimmer is not to be adjusted again during the
remainder of the alignment procedure. Now go back
to 600 kc and check the adjustment of the oscillator
slug. Perform the "rocking" alignment procedure as
described In the section on "Receiver Alignment -
General" to get maximum sensitivity. You may prefer
to make these adjustments using radio stations, one at
the low end and one at the high end of the band,
instead of the Signal Generator. This completes the
receiver alignment so disconnect the VTVM and the
Signal Generator from the receiver.
Your Model 280 Signal Generator can be used to
align the IF section and the detector section of FM
Receivers. FM stations can be used to align the RF
and converter sections of the receiver. Therefore you
can perform the complete alignment of an FM
receiver without an FM generator.
In this section we go through the alignment steps of a
popular AC-DC FM receiver. A schematic diagram of
the receiver is shown In Fig. 4. As you can see from
the diagram, one side of the AC power line connects
through the ON-OFF switch directly to the radio
receiver chassis. This makes the chassis "hot" and
presents a dangerous shock hazard. When you
connect the ground clip of your signal generator to the
receiver chassis, all the metal parts of your signal
generator are likewise hot. To protect yourself, plug
the receiver Into an isolation transformer. If you de
not have an isolation transformer, use your VTVM to
tell you when the receiver is plugged into the socket
correctly. Connect the ground clip of your VTVM to
the receiver chassis. Set the selector to read AC volts
on the 120 volt scale. Turn the receiver on-off switch
"on." Plug the receiver line cord Into an AC socket.
Touch the VTVM probe to a known earth ground,
such as the metal parts on the AC outlet, and read the
meter. Unplug the receiver and turn the plug over so
the prongs fit into the opposite slots of the AC outlet.
Again touch the VTVM probe to ground and read the
meter. In one plug position the meter will read zero
and in the other position it will read line voltage.
Leave the receiver plugged into the socket In the
position where the VTVM reads zero. You should
mark the plug so you can always plug it into the socket
in the correct position. This puts the receiver chassis
at ground potential and provides you some protection
against electrical shock.
The first things to align in an FM receiver are the IF
amplifier transformers. Let the receiver and the signal
generator warm up for at least 15 minutes. Connect
your VTVM between chassis and point A in Fig. 4.
Point A can also be identified as pin 2 of V4A. Set the
VTVM to read DC on the 3 volt scale. Connect the
ground lead of the signal generator to the chassis.
Disconnect the antenna from the receiver. Connect
the hot lead of the signal generator to the free end
(antenna connection) of the 50mmf capacitor, C4.
FM RADIO RECEIVER ALIGNMENT

Turn the receiver volume up full and set the receiver
dial to a point where you do not hear any interfering
signals. Set up the signal generator to produce 10.7
mc unmodulated RF, which is the IF of this receiver.
Do not move the Signal Generator tuning dial during
alignment. Even a small change In the generator
frequency will require redoing the receiver
adjustments. Attenuate the signal so the VTVM reads
about midscale. Adjust A1 for maximum indication
on the VTVM. Attenuate the signal generator as
necessary to keep the VTVM pointer on scale. Notice
that A1 is the bottom slug in the ratio detector
transformer. This slug is in the primary of the
transformer and is tuned to 10.7 mc. in the same way,
adjust A2, A3, A4, and A5 in that order. Remember to
attenuate the signal generator to keep the VTVM
reading on scale. Make the final adjustments with no
more signal than is necessary to give a good
indication.
Next align the ratio detector. Leave the signal
generator connected. Before you remove the VTVM
probe from point A, increase the output from the
signal generator to give a full 3 volt reading on the
VTVM. Connect two matched 100K-ohm resistors in
series from point A to the chassis. You can use 1%
precision resistors or pick two 100K-ohm resistors
that read the same on an ohmmeter. Since you will
want to save these resistors to use again for the same
purpose, you may want to connect alligator clips on
the ends and solder the center connection. Others
prefer to tack solder the resistors into the receiver.
These resistors are shown in Fig. 4 connected to point
A and ground by dotted lines. The junction of the two
resistors is alignment point C. Connect the VTVM
between point C and point B. The top of the volume
control is a convenient place to connect for point B.
Set the ohmmeter to read DC on the lowest scale.
Adjust A6 (Fig. 4) for zero reading on the VTVM.
This adjusts the secondary of the ratio transformer for
equal output from the two diodes of the detector.
Either side of the correct adjustment point will
produce a reading on the VTVM. On one side the
reading will be positive; on the other side the reading
will be negative.
The IF amplifiers and the ratio detector are now
properly aligned. Disconnect the VTVM. Remove the
two 100K-ohm resistors that you temporarily
connected into the receiver. Disconnect the signal
generator.
The RF stage and the local oscillator will be aligned
using FM stations. Connect the antenna to the
receiver or attach six or more feet of hookup wire to
the antenna terminal to act as an antenna. Connect the
VTVM probe to point A and connect the ground lead
to the chassis. Set the VTVM to read DC volts on the
lowest scale. Allow the receiver to warm up for at
least 15 minutes. The local oscillator in many FM
receivers will drift a sizable amount during warm up.
Since you are working in circuits that pass very high
frequency signals, make these adjustments very
carefully. It is best to move the adjustments only a
small amount at a time. Select a weak FM station near
106 mc or attenuate the signal from the station by
using less antenna wire. Identify the station and set the
receiver dial to that exact frequency. Adjust A7 until
you receive the selected station with maximum
indication on the VTVM. When you adjust A7, you
are changing the frequency of the local oscillator. If
you receive the station at two points in the adjustment
of A7, use the point of minimum capacitance of A7
(clockwise rotation of A7 increases capacitance).
This places the local oscillator frequency 10.7 mc
above the frequency of the incoming RF. Now adjust
A8 for maximum indication on the VTVM. Trimmer
capacitor A8 adjusts the tuned plate circuit of the RF
pre-selector amplifier. The oscillator and pre-selector
are now properly aligned at the high end of the FM
band.
Now align the pre-selector and local oscillator at the
low end of the band. Select an FM radio station near
90 mc. Identify the station and set the receiver dial to
the exact frequency of that station. Adjust A9 to
receive the station and produce a maximum indication
on the VTVM. In this receiver, A9 and A10 are known
as "padder flaps." They consist of small flaps of metal
positioned close enough to the coils to affect the
inductance of the coils. Moving the flaps closer or
farther away changes the inductance and thereby
tunes the tank circuit. After adjusting A9, adjust A10.
Move A10 as necessary to produce a maximum
indication on the VTVM.
After adjusting the pre-selector and local oscillator at
the low end of the band, it will be necessary to check
the adjustment of A7 and A8 at the high end of the
band. Repeat the procedure at the low end and the
high end, as necessary, until no further improvement
is possible. This completes the receiver alignment.
Disconnect the VTVM from the receiver.
Many FM receivers do not have padder adjustments
for tuning the RF and oscillator coils at the low end of
the band. lf adjustment is necessary, it is made by
spreading apart or squeezing together the turns of the

coil. You will find a tuning wand to be a great time
saver in making these adjustments. A tuning wand
consist of a plastic rod with a small amount of
powdered iron imbedded at one end and a piece of
brass imbedded at the other end. When a coil is
correctly tuned, you can insert either end of the tuning
wand into the coil and the output of the receiver will
decrease, if the output increases when you insert the
brass end, less inductance is needed and you must
spread the turns of the coil. lf the output increases
when you insert the powdered iron core end, more
inductance is needed and you must squeeze the turns
of the coil together. In this way, you use the tuning
wand to temporarily change the inductance of the coil
so you know whether to squeeze or spread apart the
turns of the coil.
The above procedure for aligning an FM receiver can
be used for aligning most commercial FM receivers.
Whenever possible you should consult and follow the
manufacturer's alignment instructions for the
particular set you are working on.
If you assembled your Signal Generator from a kit,
you will want to refer to this section to check the
operation of the instrument before you install it in the
cabinet.Also, you may want to check the alignment of
the Signal Generator.
If you purchased your Signal Generator already
assembled, you need not refer to this section at this
time. However, if your Signal Generator gives you
trouble at some future time, the information in this
section will help you put it back in tip-top operating
condition.
Your Signal Generator will probably operate
properly when you first turn it on. However, the
possibility exists that you have made a wiring mistake,
so check the operation before installing it in the
cabinet.
Plug the line cord into a 115-volt 60-cycle AC
supply. Turn the attenuator control clockwise to turn
the on-off switch "on". Observe the vacuum tubes.
The filaments should glow after a few seconds. Set the
high-low switch to the high position. Set the
attenuator control about mid-range. Set the band
switch to B, Set the function switch to MOD. The
Signal Generator is now set up to produce modulated
RF signals in the broadcast band. Clip or lay the
output cable near a radio receiver. Tune the radio dial
to a position where no station is being received. Now
tune the Signal Generator across the "B" band. When
the Signal Generator is tuned to the same frequency as
the radio receiver, a 400-cycle tone will be heard from
the radio.
You can check for operation of the Signal Generator
in the RF position by beating the generator RF signal
against a received radio station. Tune your radio
receiver to receive a radio station. Tune the Signal
Generator (function switch at MOD position) to the
same frequency so you can also hear the modulated
tone. You may have to attenuate the signal from the
generator so it doesn't blot out the station. Now switch
the function switch on the signal generator to the RF
position. Tune the Signal Generator a small amount
on either side of the frequency of the received radio
station. You will hear an audible beat signal that varies
in frequency as the signal generator is tuned. When
the beat signal is reduced to zero frequency, the Signal
Generator and the radio station are both producing
exactly the same frequency.
With the instrument out of the cabinet, the attenuator
controls may not have much effect on the loudness of
the signal because considerable signal is radiated
directly from the chassis. After the instrument is
installed in the cabinet the chassis will be shielded by
the cabinet and the radiated signal will come almost
entirely from the clip on the output cable.
You can check the operation of the Signal Generator
in the audio position by connecting the output to an
audio amplifier. You can use the audio section of a
radio receiver. Connect the ground clip of the output
cable to a B- (gnd) point in the radio. Clip the center
lead of the output cable to a point In the audio signal
path, such as the grid of the first audio amplifier.
Switch the function switch to AUD. The 400-oycle
audio sound can be varied in volume by adjusting the
attenuator controls on the Signal Generator.
You can check the operation of the other RF bands in
the same manner if you have a communications
receiver that will tune to these frequencies. If the
Signal Generator operates on one band, you will
undoubtedly find that it operates satisfactorily on the
other bands.
Maintenance
CHECKING OPERATION OF
THE SIGNAL GENERATOR

MOD *-3.4 VDC 110 VDC6.4 VAC *-3.3 VDC*-3.4 VDC 42 VDC0--
MOD 112 VDC 6.4 VAC5.6 VDC -6.8 VDC*5 VAC 51 VDC6.4 VAC 1.6 VDC 0
AUD -.68 VDC 06.4 VAC 0-.68 VDC 00--
AUD 132 VDC 6.4 VAC6.8 VDC -7.4 VDC*3 VAC 60 VDC6.4 VAC 1.8 VDC 0
RF *-3.2 VDC 110 VDC6.4 VAC *-6 VDC*-3.2 VDC 41 VDC0--
RF 112 VDC 6.4 VAC5.4 VDC -6.2 VDC*2 VAC 62 VDC6.4 VAC 1.6 VDC 0
1 98765432
PIN
MODE
V1
6
B
E
6
V2
1
2
A
U
7
TABLE 1: Voltage Chart for Signal Generator Model 280
Positive
Terminal
Input
Terminal
Power Supply
Rectifier
2VAC
145 VDC
105 VDCCR 1
* Varies with setting of Band Switch.
NOTE: The capacitance of the voltmeter probe
may cause the oscillator to drop out of
oscillation when the probe is touched to pin 1 of
V1. If this happens, the negative voltage across
R1 will decrease toward zero.
The above voltage readings were taken with
respect to the chassis using a VTVM and with
the line voltage at 118 VAC. Your readings may
vary +/- 20% due to normal parts tolerances.
For taking readings set controls as follows:
High-Low attenuator switch on high.
Attenuator control at 5.
Band switch atA.
Function switch as indicated in Table 1.

IN CASE OF TROUBLE
ACCURACY AND ALIGNMENT
OF THE SIGNAL GENERATOR
If your Signal Generator does not work when
assembled, look for wiring errors, poor solder
connections, and shorts between wiring or from the
wiring to the chassis. Check the output cable with an
ohmmeter to be sure there are no shorts between the
inner and outer conductors due to over-heating during
soldering. Use the voltage chart in Table 1 and the
schematic diagram in Fig. 1 to isolate the trouble to
one section or part of the instrument. If you find a
faulty part write us telling the part number and the
name of the part. We will furnish a replacement. Do
not return the faulty part unless we write and
specifically ask you to do so. Do not disassemble the
part as this may void the guarantee.
If you cannot locate the trouble yourself, you may
use our free CONAR consultation service. Write us a
letter describing in detail the trouble you are
experiencing. Make a voltage chart giving the
readings that you get on your instrument. Try to give
us enough information so we can analyze your trouble.
We will try to send you the information necessary to
get your Signal Generator back into operating
condition.
If you cannot get your Signal Generator working
yourself, you can return it for repair. If it is necessary
to do this, we will make a service charge of $7.50 plus
the cost of any parts that have been damaged due to
wiring errors.
If you return the Instrument to us for repair, write us a
letter telling us that the instrument is on the way and
describe fully the difficulty you are having. Enclose
the $7.50 minimum charge. Send check or money
order. Do not send cash. Pack the instrument in a
sturdy carton and fill the open spaces with shredded
newspaper. Ship the instrument to us by prepaid
express or insured parcel post. We will return your
instrument express collect or insured parcel post.
A carefully built CONAR Signal Generator will be
accurate enough for service work without aligning the
instrument. However, you may wish to check the
accuracy of your Signal Generator or you may want to
realign it to improve its accuracy. The instrument is
provided with an oscillator coil adjustment and a
trimmer capacitor adjustment for each band. This
enables you to adjust the oscillator circuit so that the
generator frequency corresponds exactly to the scale
readings. To do this you must have known accurate
frequencies available in the frequency band that you
are checking or adjusting.
Do not attempt any adjustment on your signal
generator until you are sure that the generator is in
error. If you attempt to make adjustments without
having known accurate frequencies available you will
probably decrease its accuracy.
All signal generators are designed as a convenient
source of signals at various frequencies. No Signal
Generator is designed as a frequency standard. Some
expensive signal generators have a frequency
accuracy of better than 1%, For service work and
receiver alignment, an accuracy within 2 to 3% is
considered quite satisfactory. Your CONAR Signal
Generator will probably fall well within this accuracy
without alignment. Careful alignment can bring the
accuracy to about 1%.
The B band on your Signal Generator can be readily
checked or aligned by using the signals from local
radio stations. You will need a radio receiver and you
must know the exact frequency that the stations
operate on. Select two stations, one whose frequency
is near the high end of the B band and one near the low
end of the B band. Before checking or aligning your
signal generator, you should perform the following
steps:
( ) Turn the signal generator on and let it warm up for
at least 15 minutes.
( ) Make sure that the red line of the dial pointer
coincides with the black line on the left (low
frequency) edge of the scales when the tuning
capacitor is fully meshed (turned maximum counter
clockwise). If not, loosen the pointer set screw and
reset the pointer.
( ) Identify the coil and capacitor adjustment for each
band by referring to Fig. 5. We suggest you use pencil
or crayon to mark the band letter on top of the chassis
between the trimmer hole and its associated coil. This
will help prevent you from accidentally turning a
wrong adjustment.
Tune the radio to receive the known frequency
station near the high end of the B band. Definitely
identify the station. Position the output lead of the
signal generator near the radio receiver antenna. Set
the signal generator function switch to RF and the

band selector to B. Rotate the signal generator dial to
the same frequency as the received radio station. You
should hear a high pitched audio signal that decreases
in pitch as you approach the frequency. This beat note
signal is the difference in frequency between the radio
station signal and the generator signal. Zero beat the
two signals by carefully adjusting the signal generator
frequency until the beat note is at minimum or zero
frequency. Now the signal generator is producing
exactly the same frequency as the radio station.
Observe the dial reading of your signal generator. The
difference between the dial reading and the known
frequency of the radio station is the error of your
signal generator at that frequency.
( ) Carefully recheck your work to be sure that the
error exists. If you decide to try to realign the B band
proceed as follows: Locate the trimmer adjustment
for band B. Set the signal generator dial to read
exactly the frequency of the radio station to which the
radio is tuned. Rotate the B band trimmer adjustment
until you again hear the beat signal. Then carefully
rock the adjustment back and forth to zero beat signal.
The signal generator is now correctly aligned at this
frequency.
( ) Tune the radio to a known frequency station whose
frequency is near the lower end of the B band. Rotate
the dial of the signal generator to indicate about the
same frequency as the radio station and zero beat the
signals. The difference between the reading on the
signal generator and the known frequency of the radio
station is the instrument error at this frequency.
( ) Correct the generator error at the low end of the B
band by adjusting the B band coil slug. Set the signal
generator to read the known frequency of the radio
station that the radio receiver is tuned to. Rotate the B
band coil slug adjustment until you hear the beat note
and then carefully rock the slug to zero beat the signal.
( ) After adjusting the slug at the low end of the band
you will have to readjust the trimmer at the high end of
the band. These two adjustments interact so you have
to repeat each adjustment several times.
After aligning the B band at the high end and the low
end. the instrument should read correctly at all points
on the B band scale. However, some small errors may
exist at other points on the B band scale. Such errors
are usually due to slightly bent plates on the tuning
capacitor resulting from rough handling. Before
attempting to correct these errors, you might consider
whether they are large enough to worry about. For
example, suppose your signal generator reads 1020 kc
when you zero beat it with a station broadcasting cn
exactly 1000 kc. Your signal generator reads one
whole graduation above 1000 kc. However, the error
is only 2%. That is 1000 kc or 1,000,000 cps x .02 =
20,000 cps or 20 kc. While 20 kc may seem like a large
error, it is cnly 2% of 1000 kc. This size error is
unimportant for servicing and aligning a radio
receiver.
You can check or align the other bands of your signal
generator if you have a Communication Receiver
available.As described for Band B, you select stations
of known frequencies at both ends of the band you are
checking. Use the proper band trimmer to correct
errors at the high end of the band and use the
corresponding coil slug adjustment to correct errors at
the low end of the band.
Harmonics of the signal generator output can be
used for checking or aligning. For example, suppose
you are receiving a known frequency radio station at
600 kc. Set the signal generator at 300 kc on the A
band. The second harmonic of the 300 kc signal is 600
kc. This second harmonic will be received along with
the radio station and the signals can be zero beat.
Using this technique you can check many additional
points on your instrument.
If you prefer, you can send the instrument to us for
alignment. For this service there will be a charge of
$7.50. If you send us your completed signal generator
for alignment, write us that the instrument is on the
way and include the service charge. Send check or
money order. Do not send cash. Pack and ship the
instrument in accordance with the instructions given
in this manual under "In Case of Trouble."
After you have checked the operation of the signal
generator, install the chassis in the cabinet. Set the
chassis upright in front of the cabinet. Place the power
cord from the inside of the cabinet through the hole in
the rear of the cabinet. Pull the power cord as you lift
up the chassis and push it into the cabinet. Be careful
not to catch the switches on the cabinet lip because the
switches may get damaged.
Fasten the front panel to the cabinet using six No. 6
self tapping Phillips nickel plated screws. Insert two
No. 6, 1/2" slotted hex head self tapping screws
through the holes in the bottom of the cabinet into the
INSTALLING THE SIGNAL
GENERATOR IN ITS CABINET

matching holes in the chassis. Tighten the screws
firmly.
Your CONAR Signal Generator is constructed of
quality parts and the instrument will ordinarily give
years of trouble-free service before any maintenance
is required. If trouble develops, service the instrument
as you would any other piece of electronic equipment.
Since tubes are the most likely cause of failure, test
the tubes first. Remove the chassis from the cabinet
and test the tubes in a tube tester.
Dangerous voltages are present in this
instrument. When you energize the instrument with
the chassis out of the cabinet, take precaution to avoid
electrical shock.
If you replace the 6BE6 oscillator tube you will want
to check the alignment of your Signal Generator.
Normal manufacturing tolerances of vacuum tubes
causes each 6BE6 tube to operate slightly differently
in the signal generator circuit. Most replacement
tubes will not cause enough change in the frequency
of the output of your Signal Generator to require
alignment adjustments. However, it is wise to check
the alignment to be sure that the replacement has not
seriously changed the output frequency. You will find
instructions for checking and alignment under the
heading of "Accuracy and Alignment of the Signal
Generator” in this manual.
You can check the voltage readings in your Signal
Generator against those given in the voltage chart in
Table I. Use Fig. 1 to locate test points. This will often
lead you to the defective component. Normal parts
value tolerances can cause quite large variations in the
actual readings from the readings given in the table. If
your instrument has been in service for many years, a
very low B+ voltage may be caused by a defective
selenium rectifier. A large ripple voltage at the output
of the power supply may be caused by a defective
electrolytic filter capacitor.
Hard usage of the output cable can cause a short
circuit in the coaxial cable. Frequent bending of the
cable may have caused the braided shield to fray. If
these frayed wires of the shield come in contact with
the center wire, it will short circuit the output of the
signal generator. This condition can be quickly
checked by using an ohmmeter. Connect the
ohmmeter between the ground lead and the "hot" lead
of the output cable. The ohmmeter should read near
infinite resistance. A zero reading or a reading of only
a few ohms indicates that there is a short circuit in the
cable.
If your instrument does not operate after replacing a
defective tube, check the circuitry around that tube. A
shorted tube may have caused excessive current to
flow through a resistor. The excess current may have
caused a resistor to burn out or change value. Use an
ohmmeter to check the values of resistors that could
have been affected.
If your Signal Generator operates intermittently on
some ranges, check the switches for dirty contacts.
They can be cleaned by using any good switch contact
cleaner.
If your Signal Generator develops a trouble that you
cannot locate, use the free CONAR consultation
service. Write us a letter explaining the exact nature of
your trouble. Include the results of any tests that you
have conducted in trying to locate the trouble. Make a
voltage chart giving the readings that you get on your
instrument. Try to give us enough information so we
can analyze your trouble. We will try to send you the
information necessary to get your Signal Generator
back into operation.
If, after the warranty period has expired, a defect
develops in your instrument that you are unable to
repair yourself, you may return it for repair for which
there is a minimum charge of $7.50 plus the cost of
any parts. This minimum charge is necessary to cover
the cost of handling, inspecting, and making minor
repairs. If you return the instrument to us for repair,
write us a letter telling us that the instrument is on the
way and describe fully the difficulty you are having.
Enclose the $7.50 minimum charge. Send check or
money order. Do not send cash. Pack the instrument in
a sturdy carton and fill the open spaces with shredded
newspaper. Ship the instrument to us by prepaid
express or insured parcel post. We will return your
instrument express collect or insured parcel post.
CORRECTIVE MAINTENANCE
CAUTION: