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Section Page Section Page

1. GENERAL DESCRIPTION . . . . . . . . 1 5-3. Models 108, 109 Lo\<-Frequency
Calibration . . . 14
l-l. General . . . . . . . . 1 5-4. Model 108 High-Frcqurnc)
1-2. Models 108, 109 Differences . 1 Calibration . . . 14
l-3. Specifications. . . . . . . . 2 5-5. Model 109 High-Frequency
1-4. Applications. . . , . . .3 Calibration . . . 15
l-5. Accessories . . . . . . .3 5-6. Low-Frequency Response
l-6. Equipment Shipped . . . . .3 Check........... 16

2. OPERATION . . . . . . . . .5 6. ACCESSORIES. . . . 19

2-1. Terminals . . . . . . . . . 5 6-l. Model 1081 Power Supply 19
2-2. Operating Procedures. . . . . 5 6-2. Model 1042 Accessory Kit . . 19
2-3. Cascading . . . . . . . . . . 5 6-3. Model 1082 Mounting Plate . 20
2-4. Gains Other Than 10, 100
1000 and 10,000. . . . . . . 6 7. REPLACEABLE PARTS. . . . . . . . . 21
2-5. Open Circuit Operation. . . . 6
2-6. Amplifier Noise . . . . . . . 6 7-l. Replaceable Parts List . . . 23
2-7. Rise Time . . . . . . . . . . 6 7-2. How to Order Parts . . . . . 23
2-8. Delay Time. . . . . . . . . . 6 Models 108, 109 Replaceable
2-9. Ground Loops. . . , . . . . 7 Parts List. . . . . . . . . 24
Z-10. Stray Fields. . . . . . . . 7 Model 1081 Replaceable Parts
List. . . . . . . . . . . . 26
3. CIRCUIT DESCRIPTION ....... . 9 Models 108, 109 Schematic
Diagram 17971D. . . . . . . 29
3-1. General .......... . 9 Model 1081 Schematic Diagram
3-2. Amplifier Design. ..... . 9 17966C. . . . . . . . . . 30

4. SERVICING ............ . 11 + Change Notice Last Page
4-1. General .......... . 11
4-2. Servicing Schedule. .... . 11
4-3. Parts Replacement ..... . 11
4-4. Troubleshooting ...... . 11
3~ Yellow Change Notice sheet is
5. CALIBRATION ........... . 13 included only for instrument
modifications affecting the
5-l. General .......... . 13 Instruction Manual.
5-2. Calibration Schedule. ... . 14



l-l. GENERAL. The Keithley Models 108 and 109 are small, 12-ounce Xl0 gain amplifiers.
The Model 108 is tuned for a wideband frequency response; the Model 109 is tuned ior pulse
response. (See Figures 9 and 10 for illustrations of the two responses.) Both ?lodels re-
quire an external power supply, preferably the Keithley Model 1081 Power Supply, which
can drive up to three of these units at one time.

a. The Model 108 bandwidth is from 1 kc to 180 MC (-3db). Response Erom 2.5 kc to
150 MC is flat 20.5 db. Voltage gain is 10 (20 db) when terminated into a 50-ohm load.
Up to four Model 108 Amplifiers may be cascaded for gains to 10,000, or one may be used
with other amplifiers to increase total gain by 10. The input impedance is 50 ohms.
Noise is less than 30 microvolts rms referred to the input.

b. The Model 109 Pulse Amplifier has a rise time of less than 3 nanoseconds (10:: to
90%). Overshoot is less than 2%, pulse width for a 10% droop is 30 microseconds. Other
specifications are the same as for the Model 108. Four Pulse Amplifiers may be cascaded
for gains to 10,000, or one may be used with other amplifiers to increase total gain by 10.


a. The Models 108 and 109 differ only in their tuning. The circuits and the parts are
identical. Most of the Instruction Manual applies to both units. Where there are differ-
ences - such as application suggestions and calibration - the models are identified.

b. Specifications and operations in this Manual assume using the Keithley Model 1081
PO`Wer Supply to power the Amplifier. It is recommended that this Power Supblv be used to
ob tai .n the maximum benefit from the Amp fier.

10s AMPLIi=,ER

I:IGLlRE 1. Keithley Instruments i"`Lb"KL L. nelr"Ley ~"strumenrs
tlode1 108 Wideband Amplifier. Model 109 Pulse Amplifier.

0465R 1

Model 108 (when powered by Model 109 (when powered by
the Model 1081 Power Supply) the Model 1081 Power Supply)

Frequencyl: -3db 1 kc and 180 MC
?0.5db 2.5 kc to 150 MC

Rise Time* (10% to 90%) Less than 3 nanoseconds Less than 3 nanoseconds

Overshoot3 - Less than 2%

Pulse Width for 10% Droop: - 30 microseconds

Input Impedance: 50 ohms 50 ohms

Voltage Gain (into 50-ohm 10 (20 db) 10 (20 db)
characteristic impedance) ?2% at 10 kc i-2% at 10 kc

Maximum rms Noise4: 30 microvolts (7 db) 30 microvolts (7 db)

Maximum Output (into 50-ohm 1.4 volts peak-to-peak 1.4 volts peak-to-peak
characteristic impedance)

Maximum Overload: ac, 20 volts peak5 ac, 20 volts peak5
dc, 2.5 volts dc , 2.5 volts

Overload Recovery6 Less than 50 nanoseconds Less than 50 nanoseconds

Delay Time' Less than 5 nanoseconds Less than 5 nanoseconds

Change in Output Amplitude
for a 10% Line Voltage Change
(when powered by Model 1081): Less than 20.1% Less than *O.l%

1) db variations add when amplifiers are cascaded.
2) Maximum rise time for 3 amplifiers in cascade is less than 4 nanoseconds.
3) Overshoot for amplifiers in cascade is 3% or less.
4) Noise referred to input measured from 10 cps to 100 MC. Noise of cascaded am-
plifiers is equal to noise of first amplifier only.
5) Continuous input power should not exceed l/8 watt.
6) Using a 100X overload test pulse 100 nanoseconds wide with 5-nanosecond fall
time to within 1% of base line. A shorter pulse duration, a slower fall time
or less overload shortens recovery time.
7) Delay times add when amplifiers are cascaded.

CONNECTORS: Input and Output: n type. Power: Amphenol 126-214

POWER: +16 volts.dc and -12 volts dc; or 28 volts dc floating; ?5% accuracy; 50 milliam-
peres current (1.4 watts); +O.l% stability; Z-millivolt peak-to-peak maximum ripple; lOO-
microfarad filter from each power terminal to ground.

DIMENSIONS, WEIGHT: 3 inches high x 2-l/4 inches wide x 3-3/4 inches deep; net weight, 12 oi

ACCESSORIES SIIPPLIED: Mating power connector; mating input and output connectors.

2 0565R


a. The Model 108 Wideband Amplifier is used as a general Laboratory pre-amplifier in
audio, radar, IF, TV and VHF work. It can be used with all types of oscilloscopes. 11s
low noise permits amplification of signals in the microvolt region at low and high Irequev
ties. Because of its small size, it can be designed into other equipment.

b. The Model 109 Pulse Amplifier is designed co amplify non-sinusoidal wave corms :.:ith
a fast rise time, minimum overshoot and minimum ringing. Common applications include use
with oscilloscopes, high-speed counters, pulse-height analyzers and phoro multipliers.

L-5. ACCESSORIES. Refer to Section 6 for complete descriptions of the following Ampli-
fier accessories.

a. Model 1081 Power Supply can power one, two or three Model 108 or 109 Amplifiers.
The POWer Supply operates from 105-125 or 210-250 Volt, 50-400 cps line sources; pocrr
rating is 12 watts. Its dimensions are the same as the hmplifi.ers; net weight is l-l,'?

b. Model 1042 Accessory Kit provides useful adapters, terminations and tee for use with
the Amplifier. The Kit accessories, contained in a convenient case, art` described in Scc-
tion 6.

c. Model 1082 Mounting Plate adapts the Amplifiers and the Hodel LO81 for mounting LO
another surface.

d. Model 1083 Cable allows using the filodels 108 and 109 with the Keicbley l$z,dcA1s lO(, ilnd
107 Amplifiers.

FIGURE 3. >lodrl 1081 Power Supply Used twiti> 'Three Elodel 109 I'ulsc Amplifiers. Tltc suppl)
will power 1, ? or 3 Amplifiers. See Scdtior 6 ior the Power Supply description.

02h6R 3

1-6. EQUIPMENT SHIPPED. The Models 108 and 109 are factory-calibrated and are shipped
with all components in place. All units are shipped for bench use. The shipping carton
contains the Instruction Manual, a mating power connector and mating input and output




a. INPUT and OUTPUT Receptacles. INPUT (front panel) and OUTPlJ'~ (rear panel) Recepr;i-
cles are n-type. Input impedance is 50 ohms. N-type connectros are used for their bccter
impedance characteristics and less leakage at higher frequencies than other popular con-

b. POWERSocket. The POWERSocket is a 4-pin connector. It is compatible with the
power cable supplied with the Model 1081 Power Supply. Schematic Diagram 1797LD shows
the pin connections and voltages (refer to 5103).


a. No control settings or preliminary adjustments are needed to operate either Ampli-
fier. Both can be used immediately after they are connected to the ~lodel 1081 Power Suppl)


The Amplifiers have n-type receptacles (Mil. No. 680/U). The Model 1042
Accessory Kit contains adapters to connect other type plugs to the Amplifier.
Section 6 describes the Kit.

b. Connect the Power Supply and associated equipment, such as an oscilloscope, on the
same power line to avoid ac ground Loops. Otherwise, the output signal from the Amplifi~cr
may tend to be modulated by the ground Loops. To further minimize ground loops, it may be
necessary to use isolation plugs on power line plugs of the Power Supply and the associa-
ted equipment. If a power supply other than the Model LO81 is used, put 100-,lf filter
capacitors from + and - to ground.

c. Use coaxial cables for connections,
especially if working above 1 MC. Up to six Keithley
feet of coaxial cable may be used on the Input: - AMI'LI- -Output:
Amplifier input and up to 12 feet on the out- 6 feet FIER 12 feet
put, if the output cable is terminated with max. max.
50 ohms. Longer cables may be used, but the
Amplifier may not meet the flatness or over-
shoot specifications. All cables used must
have a 50-ohm characteristic impedance.
- 50-r:
NOTE source A
The Model LO9 has no phase reversal
on pulse. If the pulse is positive
at the input, it is positive at the
output, If it is negative at the FIGURE 4. Amplifier Cable Connections.
input, it is negative at the output. Maximum recommended cable length to input
is six feet; from output, 12 feet. If
^ _
2-3. CASCfi"ING. longer cables arc used, the specified flnt-
ness or overshoot may not be achieved. USC
a. Up to four AmpliTiers may be cascaded only coaxial cables.

0'6611 3

together for gains of 100, 1000, or 10,000. The final Amplifier output should not exceed
1.4 volts peak-to-peak into a 50-ohm load. Higher outputs exceed the limits of the am-
plifier stages and distortions will result. A bandpass filter is recommended for lO,OOO-
gain hookups to reduce the noise level.


When using the 108 or 109 with the 106 or 107, "se the 1083 cable for connection
into the 106 and 107 power outlet.

b. Use the n-type male-to-male adapter from the Model 1042 Kit to cascade Amplifiers
directly to each other. The Model 108 may also be used in cascade with the Keithley
Models 104 and 106 Amplifiers. The Model 109 may also be used in cascade with the Models
105 and 107 Amplifiers.

2-4. GAINS OTHER THAN 10, 100, 1000 AND 10,000. For gains in between the cascaded values,
"se attenuator pads in series with the Amplifier. When two Amplifiers are cascaded, use
the attenuator pad on the last Amplifier OUTPUT Receptacle for input signals below 15
millivolts peak-to-peak for the best signal-to-noise ratio. For example, a l-millivolt
rms input signal is amplified 20 times (26 db) using a 14-db attenuator pad on the last
Amplifier output. Maximum input noise of each amplifier is 30 microvolts rms. Noise at
the last output is 3 millivolts rms. When the noise is attenuated five times through the
14-db pad, its level is 0.6 millivolt rms. Signal-to-noise ratio is approximately 28:l.
If the 14-db attenuator pad were used at the first Amplifier input, the output noise would
be 3 millivolts rms. Signal-to-noise ratio would be approximately 6:1, or four times
worse than previously.

2-5. OPEN CIRCUIT OPERATION. The specified Amplifier gain is into a 50-ohm load. The
gain changes for an open circuit. Output impedance is approximately five ohms below 10
megacycles, increasing as the frequency increases. Below 10 megacycles, therefore, the
gain into an open circuit is approximately 10.5 to 11. Above 10 megacycles, the gain
increases to approximately 18 (25 db) at 150 megacycles. The Amplifier will not oscillate
into an open circuit at any frequency, although standing waves become apparent at the
higher frequencies. The magnitude of the waves depends directly on cable length and

2-6. AMPLIFIER NOISE. The main sources of noise are the transistors and any power supply
ripple. Since all noise is referred to the
input, the output noise will be the ampli- IO% LIWEI~II" GAIN IHL
GAlY _YlllMUY mo*OK!
DlwM 01 LYPllllER
fier input noise times the amplifier gain (10).
The noise is measured at the output and re-
ferred back to the input. When two Ampli-
fiers are cascaded, the noise of the second G; /
amplifier is not significant because noise adds 28%
as the square root of the sum of the squares. 9 : ~-1


a. The rise time is defined as the time lli I1 I 1 1 I
1ow 1oow.I"/I I
101110011I", ,ou ,ool ,6,
needed for a signal to rise from 10% to 90%
of its final value. Specifically, for I"IPUtK"
amplifiers, rise time is the time needed FIGURE 5. Models 108 and 109 Gain Linearity
for the amplifier to go from 10% to 90% The gain linearity falls within the limits
of the final value of the input signal shown above from 2.5 kc to 150 Mc.

6 0266R

times the amplifier gain. Rise time is measured only with a pulse whose rise time is
faster than the amplifier's, When amplifiers are cascaded, the rise times add in qundra-
ture (square root of the sum of the squares).

b. The slight overshoot of a very high frequency pulse can be eliminated in Lhf >lodcl
108 by detuning the high-frequency response slightly. The Model 108 is tuned for msximum
gain flatness for a continuous signal. The Model 109 is already tuned lor minimum ovcr-

2-8. DELAY 'TIME. Delay time is the transit time taken by a signal to go from the ampli-
fier input to output. Because delay times are a physical constant, they add for cascaded

2-9. GROUNDLOOPS. A common source of errors when amplifying Low-lcvcl signals is ground
loops. This is a current - line or other frequency - flowing in a ground lead impedance
which results in a voltage in addition to the desired signal voltage appearing ac tllc
input terminals of the amplifier. Although the origin and mechanism of ground loops nrc
difficult to explain and trace, their effects can be reduced in several ways.

a. Make all ground lead impedances as low as possible.

b. Employ only coaxial hookups wherever possible.

Z-10. STRAY FIELDS. Stray fields can induce unwanted emf's in the test system. 'The in-
accuracies due to these fields become more significant as measurements become more scan-
sitivc. Induced emf's may be reduced by using coaxial cable having minimum loop area and
by using cables of minimum length.

0266R 7



a. Both Amplifiers are of conventional RC-coupled cascade design, using negative fccd-
back. There is no inductive peaking. The wide bandwidth is achieved by using selected
epitaxial mesa transistors with a. l-gigacycle ft.

b. Careful circuit design allows for maximum performance. Point-to-point wiring mini-
mizes lead inductance. Silver plating on the chassis eliminates ground loops and reduces
resistance due to skin effect at high frequencies. Using solid-state components, hermet-
ically sealed tantalum capacitors and metal film resistors insures excellent stabilit)
and long. trouble-free operation.


Refer to Schematic Diagram 1797LD at the back of the Manual for circuit

3-2. AMPLIFIER DESIGN. Each Amplifier us-
es three high-frequency transistors, two in
cormnon emitter cascade configuration and
the third being an emitter follower for the
output. A high negative feedback loop is
used for gain stability.

The input is shunted by a 50-ohm me-
tay'film resistor (RlOZ), compensated for
a nominal 50-ohm input impedance across the
band. The input signal is applied to tran-
sistor QlOl. Transistors QlOl and 4102 am-
plify the signal and apply it to the emitter
f"ll"Wer, transistor Q103, which provides
low output impedance and higher power capa-
bilities than the amplifier stages.

b. The feedback loop for the two ampli- gram shows the stage design used in the 2-
fier stages is through resistor Rll6 and stage amplifier. Resistors Rl and R2 and
capacitor CllO. The output of transistor the collector bias voltage drop provide a
9102 is divided by resistor Rll6 and the bias voltage divider, which stabilizes the
network, resistors R109, RllO and Rlll. base voltage. Resistor Rl supplies dc feed-
Potentiometer Rlll adjusts the gain at the back. To eliminate degeneration caused by
lower frequencies. Trirmners C103, C112, the ac feedback, Rl is divided into two
Cl15 and Cl18 adjust the feedback at higher parts, Rla and Rl . Capacitor Cbp bypas-
frequencies, since the divider becomes pri- ses the ac from tie midpoint
P to ground.
marily capacitive.

c. Each stage uses dc feedback from collector to base. The feedback loop for the first
stage, transistor QlOl, consists of two resistors, R105 and R106. Capacitor Cl05 is at
the midpoint between the two 2,2-kilobm resistors to eliminate ac feedback. Resistors
R114 and R115 and capacitor Cl08 provide the same function for transistor Ql02.

0465R 9


4-l. GENERAL. Section 4 contains the maintenance and troubleshooting procedures for the
Models LO8 and 109. Follow these as closely as possible to maintain the instrument's

4-2. SERVICING SCHEDULE. The Models 108 and 109 require no periodic maincennncc beyond
the normal care required of high-quality electronic equipment. Occasional C~CCKS 3s the
frequency or pulse response of the Amplifier should show the need for any ;ld~justocnL. SO
part should need frequent replacement under ordinary use.


a. The Replaceable Parts List in Section 7 describes the electrical components of the
Amplifiers. Replace components only as necessary. Use only reliable replacements which
meet the specifications. Check the frequency or pulse response after any transiscar is

b. The transistors are selected for parameters which allow wide frequency response.
Order these parts only from Keithley Instruments, Inc., or its representatives.


Physical location of components greatly affects high frequency response. Put
replaced parts and their leads in their exact previous position.


a. The procedures which follow give instructions for repairing troubles which might
occur in the ModeLs 108 and 109. Use the procedures outlined and use only speciiied re-
placement parts. Make sure the external circuits are checked. Table 1 lists equipment
recommended for troubleshooting. If the trouble cannot be located or repaired, contact
the nearest Keithley representative.

Instrument Use

Keithley Instruments Model 121 True RMS Measures ac voltages

Keithley Model 153 DC Microvolt-Ammeter, Measure dc voltages
3% accuracy, 20 megohm input resistance

Simpson Models 260 and 650 Transistor Check transistors
Beta Testers

Tektronix Type 504 Oscilloscope, passband Observe wave forms
dc to 450 kc

TABLE 1. Equipment Recommended for Troubleshooting. Use these instruments or their

0266R 11

Trouble Probable Cause Remedy

Amplifier will not operate Faulty transistor Check QlOl, Ql02, Ql03; replace
if faultv

Noise with Amplifier Faulty transistor Check QlOl, QlO2, Q103; replace
exceeds 30 microvolts rms if faulty

Excessive ripple from Check power supply. Check
power supply filters ClOl, C106, Cl16, C122,
Cl23 and C124.

Gain is more or less than 10 Potentiometer Rlll out Adjust Rlll per paragraph 5-3
of adjustment

Model 108 frequency Amplifier out of cali- Calibrate per paragraph 5-4
response not flat within bration

Model 109 exceeds over- Amplifier out of cali- Calibrate per paragraph 5-5
shoot specification bration

Rise time of Amplifier Amplifier out of cali- Adjust Model 108 per paragraph
not within swcification I bration I 5-4. Model 109 oer oaraaarah 5-:

Input impedance not Faulty R102 or Cl02 Check R102 and ClO2; replace
50 ohms I I if fault-v

TABLE 2. Models 108 and 109 Troubleshooting. Refer to paragraph 4-4, b, before trouble-
shooting the Amplifier.

b. Before troubleshooting the Amplifier, check the external circuits, especially the
power supply. Make sure the Amplifier output is terminated into a good 50-ohm load. Check
the coaxial cables and connections. Check the performance of the signal generator and
other instruments. (The Amplifier will faithfully amplify any signal fed to it; a poor in-
put results in a poor output.) Make sure the output signal does not exceed 1.4 volts peak-
to-peak. If the external circuits are good, check the Amplifier itself.

c. Table 2 contains troubles which might occurs with the instrument. If the repairs
indicated in the table do not clear up the trouble, continue to search through a circuit-
by-circuit check. Refer to the circuit description in Section 3 to find the more crucial
components and to determine their function in the circuit. The complete circuit schematic
diagram, 17971D, is in Section 7.

d. If the instrument will not operate, check the power source. If it is satisfactory,
continue to isolate the trouble.

e. 'The Schematic Diagram indicates the transistor terminal voltages referenced to chas-
sis ground. Measure the dc voltages to zlO% of indicated value with a dc voltmeter.

12 0665R



a. The following procedures are recommended for calibrating and adjusting the >lodels
108 and 109. Use the equipment recommended in Table 3. If propcr facilities arc not
available or if difficulty is encountered, contact Keithley Instruments, inc., or its
representative to arrange for factory calibration.

b. Three calibrations are in the procedures: low-frequency calibration, higlr-frequen-
cy wideband calibration and pulse calibration. In addition, paragraph 5-6 outlines test
procedures to check response.

c. If the instrument is not within specifications after the calibration, follow the
troubleshooting procedures or contact Keithley Instruments, Inc., or its representative.

Instrument Use

General Radio GR-874 type attenuators, High frequency calibration
3 db, 6 db, 10 db and 20 db

General Radio CR-874-WM50 50-ohm termin- Amplifier termination
ation (also found in Keithley Instruments
Model 1042 Accessory Kit)

Hewlett-Packard Model 202A Audio Oscillator, Signal generator for low-frequency cali-
20 cps to 40 kc, 22% bration

Jarrold Electronics Model 900-B Sweep Sig- Signal generator for Model 108 band
nal Generator (includes Model D50 Detec- response
to=), 500 kc to 1200 MC

Keithley Instruments Model 121 True RMS Measure ac voltages

Tee and adapters (found in Keithley Instru- Hook up calibration circuits
ments Model 1042 Accessory Kit)

Tektronix Type 111 Pulse Generator, 0.5-nsec Check Model 109 pulse response
rise time, 2 to 20-nsec pulse duration

Tektronix Type 504 Oscilloscope, passband Check wave form during tuning and view
from dc to 450 kc sweep display of Model 108

Tektronix Type 561A Oscilloscope, with dual View Model 109 pulse response
trace plug-in sampling units, 0.4-nsec rise

TABLE 3. Equipment Recommended for Models 108 and 109 Calibration. Use these instruments
or their equivalents.

0565R 13

plifier response yearly or when transistors
are changed. Refer to paragraph 5-4 (Model
108) or S-5 (Model 109) for procedures; re-
calibrate completely if the response is not 5-4 (108) I
correct. Always recalibrate the high-fre-
quency gain if the low-frequency gain is

I Low Frequency I Rlll 1 14 1 5-3 1

BRATION TABLE 4. Models 108, 109 Internal Controls.
The Table lists all internal controls, the
a. Remove the Amplifier cower by remov- figure picturing the location, and the
ing the four screws. Connect the Amplifier paragraph describing the adjustment.
to the Model 1081 Power Supply.

b. Connect the Model 202A Oscillator to the Amplifier INPUT. Adjust the oscillator sig-
nal for 50 millivolts rms at 10 kc. Connect the Model 121 Voltmeter, Type SO4 Oscillo-
scope and 50-ohm termination to the Amplifier OUTPUT. The output signal should be 500
millivolts rms *lo millivolts. Adjust potentiometer Rlll (Figure 14), if necessary, for
this output.

c. Monitor the output signal on the oscilloscope and check for distortion.

The low-frequency calibration establishes the base for the high-frequency re-
SpO*Se. Therefore, tune the Amplifier at the high frequencies after tuning
it at the low frequencies.


a. Remove the Amplifier by removing the four screws. Connect the Amplifier to the Model
1081 Power Supply. Connect the Model 900-B Sweep Generator to the Amplifier INPUT direct-
ly. See Figure 7. Connect the Amplifier OUTPUT to the Model D50 Detector.

b. Adjust the generator signal to 50 millivolts rms and center the frequency at 100
megacycles. Adjust the oscilloscope for a vertical display of 5%/cm.

Model 900-B

I ?

FIGURE 7. Block Diagram for Model 108 High-Frequency Calibration. Refer to Table 3 for

14 0565R


Use only an insulated alignment tool in adjusting the trimmers. DC biases
are present across trimmer C118, and a screwdriver would short out the bia-
ses and possibly damage transistor Q102.

c. The low-frequency gain should be previously set (paragraph 5-3). Set trimmers C103,
Cl12 and Cl15 (Figure 14) to their minimum values. Set trimmer Cl18 (Figure 12) to mini-
mum by noting when the lowest high-frequency response curve appears on the oscilloscope.
Set trimmer Cl15 to approximately l/3 of maximum to keep the Amplifier from oscillatin>:
into an open circuit at higll frequencies. Set trimmer Cl03 near its maxiorunr. Set trimmer
Cl12 to approximately l/2 maximum. The response should rise at about 50 to 100 NC.

d. Increase trimmer C118, watching the response curve on the oscilloscope. wl'hcn tile
response looks like a straight line - either rising or descending - stop adjusting C118.
Adjust trimmer Cl12 to bring the high end up or down to the proper gain level. If till?
mid-range gain (between 50 and 100 MC) is not flat, alternate ad.justing trimmers CL03 and
Cl18 until the response is flat. If necessary, i-e-adjust trimmer Cl12 to bring the high
end in perfectly. Response should be flat to at least 150 MC (refer to Figure 9).

e. Insert a 3-db pad and re-adjust the oscilloscope for a vertical of X/cm. Check for
a response of 5%. Using the oscilloscope vertical position control, put the display trace
on a reference line. Remove the 3-db pad. The 180-megacycle point should bc above the
previously set reference l.ine.


a. Remove the Amplifier cover by removing the four screws. Connect the Amplifier to the
Model 1081 Power Supply.

b. Connect the Type 111 Pulse Generator to the Sampling Oscilloscope. use attenuators
(approximately 26 db) to adjust for a 0.7-volt peak pulse on the oscilloscope, Use the
delay cable on the pulse generator to adjust the pulse width to approximately 20 nanosec-
onds. Set the oscilloscope horizontal sweep to 5 nanoseconds/cm and the vertical sensitiv-
ity to 200 millivolcslcm. If necessary, use the pretriggcr output of chc pulse generator
to synchronize the oscilloscope. Note the amount of: overshoot and the shape on the pul-
se's leading edge.

The Amplifier is being calibrated at maximum output. Do not put in larger
pulses than specified. This will cause overshooting and result in an impro-
perly calibrated amplifier.

c. Add a tee (included in the Model 1042 Kit) and 20.db attenuator; connect the pulse
generator to the Amplifier INPUT. Set Figure 8. Connect the Amplifier OUTPUT Co the
oscilloscope's other vertical input. Note the oscilloscope has 50-011111
input impedance,
which terminates the Amplifier output.


Use only an insulated alignment tool to adjust tile trimmers. DC biases are
present across trimmer Cll8, nnd a screwdriver would short out tile hiascs anti
possibly damage transistor Q102.

06651~ 15

Dual Channel
Sampling Type 111
Oscilloscope Pulse

FIGURE 8. Block Diagram for Model 109 High-Frequency Calibration. Refer to Table 3 for

d. The low-frequency gain should be previously set (paragraph 5-3). Set trimmers ClO3,
Cl12 and Cl15 (Figure 14) and Cl18 (Figure 12) to their minimum values. Set trimmer Cl15
to approximately l/3 of its maximum value. Adjust trinuners Cl03 and Cl12 so that the
output pulse looks exactly like the input pulse (Figure 11). If the input pulse has less
than 1% overshoot and ringing, adjust trimmers Cl03 and Cl12 for less than 1% overshoot
and ringing on the output pulse. Keep trimmer Cl18 at its minimun value.

e. Increase the oscilloscope sensitivity to 5 millivolts/cm and view the pulse tops.
Slight adjustments of trimmer Cl15 may be necessary to make the output pulse exactly like
the input pulse, except for the rise time.

5-6. LOW-FREQUENCY RESPONSECHECK. Connect the Model 202A Oscillator to the Amplifier
INPUT. Adjust the oscillator signal to 50 millivolts rms at 10 kc. Use the Model 121
Voltmeter to monitor the Amplifier output. Terminate the output into 50 ohms. The out-
put voltage at 10 kc should be 500 millivolts rms ?2%. Gradually decrease the signal
frequency. The output amplitude should not vary more than 5% until 2.5 kc.

16 0565R

FIGURE 9. Models 108 and 109 Bandwidth FIGURE 10. Models 108 and 109 Overshoot
Characteristics. The Model 108 is widk- Characteristics. The Model 108 is wide-
band tuned; the Model 109, pulse tuned. band tuned; the Model 109, pulsf tuned.
The response is from 0 cps (extreme left) The oscilloscope is set far 5 nscc/cm
to 240 MC; each pip represents 10 MC. horizontal, 0.2 v/cm vertical. The pulse
Display signal of 50 mv rms is from a amplifier has minimum pulse distortion at
sweep generator. The excellent flatness the expense of flatness (see Figure 9).
of the wideband amplifier is gained at the
expense of overshoot and ringing on pulses.

FIGURE 11. Pulse Fidelity of Model
109 Pulse Amplifier. Note bow the
output pulse follows the input pulse.

0665R 17

FIGURE 12. capacitor Locations. The INPUT FIGURE 13. Resistor Locations. The INPUT
Receptacle is at the top of the illustra- Receptacle is at the top of the illustra-
tion. Both the Models 108 and 109 have the tion. Both the Models 108 and 109 have the
same component locations. same component locations.

FIGURE 14 (left). Component Locations,
Reverse Side. The INPUT Receptacle is at
the top of the illustration. Both the
Models 108 and 109 have the same component

18 0665R



a. GfZ"C2Xll. The Keithley Model 1081 Power Supply furnishes the power required for one,
two or three Models 108 and 109 Amplifiers. No adjustment is necessary. Refer to Section
7 for the Power Supply Replaceable Parts List and Schematic Diagram.

b. Specifications.

Output: As required for 1, 2 or 3 Models
108 and 109 Amplifiers. 28 volts dc float-
ing; ?5% accuracy; 150 milliamperes current;
fO.l% stability; 3-millivolt peak-to-peak
maximum ripple.

Power Required: 105-125 or 210-250 volts,
50-400 cps, 12 watts.

Dimensions, Weight: 3 inches high x 2-l/4
inches wide x 3-3/4 inches deep; net weight,
l-1/2 pounds.

Accessories Supplied: Three Power Cables
3 feet long for connecting the Model 1081
to the Model 108 or 109 Amplifier.

c. Operation. Use the Power Cable to con-
nect the Power Supply to the Amplifier. One,
two or three Amplifiers can be connected at
one time. Connect the Model 1081 to the po-
wer line. Snap the front panel slide switch
on to turn the instrument on. No warm-up GIJW 15. Keithley Instruments Model 101
time or adjustment is necessary. For 234- wer Supply.
volt power sources, refer to Schematic Dia-
gram 17966C for rewiring the transformer.

d . Circuit. (Refer to Schematic Diagram 17966C.) The Model 1081 is relatively simple
for its specifications. Unregulated voltage from the transformer, Tl, is rectified by
diodes DI.01 to D104 and filtered by capacitor ClOl. The voltage is applied to transistor
Ql , connected as a series regulator. The output is sampled by resistors R106 and R108
and compared to the voltage across zener reference diode D106. Any voltage difference is
amplified by transistors Q2 and Q3, operating as a differential voltage amplifier, and
applied to the series regulator. The fuse is in series with the output. If the Power sup-
ply is overloaded, the fuse will blow. Ordinarily, the fuse will not blow, even if Ampli-
fiers arc connected or disconnected while the Power Supply is on.

6-2. ?lODEL 1042 ACCESSORYKIT. The Model 1042 Accessory Kit provides useful adapters, n
50-ohm termination and a tee for USC with the Amplifiers. The Kit cast is 2 inches high
x 12 inches wide x 8 inches deep with polyethylene-foam compartments. It ireiglis npprosi-
matcly tlircc pounds.

0665R 19

6-3. MODEL 1082 MOUNTING PLATE. (Refer to Figure 16 for dimensions).

a. The Model 1082 enables a Model 108, 109 or 1081 to be installed in a system. It
provides a,mounting surface for 0. E. M. applications.

b. To mount an instrument on the Plate, remove the four feet from the Amplifier or
Power Supply. Attach the Plate to the instrument with the No. 4 flathead screws. Make
sure the screw heads are flush with the Plate to avoid interference. The Plate and instru-
ment may be mounted to another surface in any desired position.

Item Keithley
?ig. 15 Description Part No.

1 50-ohm Termination, General Radio Type 874 cs-159
2 Adapter, male n to female uhf cs-114
3 Adapter, male n to female bnc CS-116
4 Adapter, male n to male n cs-158
5 Adapter, male n to General Radio Type 874 cs-109

6 Adapter, n-type tee cs-157
7 Adapter, male n to General Radio Type 874 cs- 109
8 Adapter, male n to male n CS-158
9 Adapter, male n to female bnc CS-116
10 Adapter, male n to female uhf cs-114

TABLE 5. Contents of Model 1042 Accessory Kit.

FIGURE 15. plodcl 1042 Accessory Kit. See Table 5 for contents.

20 0665R

FIGURE 16. Dimensions of the Model 1082 Mounting Plate.

0266 21


7-1. REPLACEABLE PARTS LIST. The Replaceable Parts List describes the components of the
Models 108 and 109 Amplifiers and the Model 1081 Power Supply. Both Amplifiers "se the
same components. The List gives the circuit designation, the part description, a suggested
manufacturer, the manufacturer's part number and the Keithley Part Number. 'Tllf last col-
umn indicates the figure picturing the part. The name and address of the manufacturers
listed in the "Mfg. Code" column are in Table 7.


a. For parts orders, include the instrument's model and serial number, the Kcithlc!
Part Number, the circuit designation and a description of the part. All structural parts
and those parts coded for Keithley manufacture (80164) must be ordered from Kcithley
Instruments, Inc., or its representive. In ordering a part not listed in the Replaceable
Parts List, completely describe the part, its function and its location.

b. Order parts through your nearest Keithley representative or Sales Service Department,
Keithley Instruments, 1~.

M or meg mfga (106) or megohms
m milli (10`3)
CerT Ceramic, 'Tubular Mfg. Maanufacturcr
CerTr Ceramic Trimmer Mil. No. Nilitary Type Number
Comp Composition MtF Metal Film
compv Composition Variable MY Mylar

DCb Deposited Carbon

ETB Electrolytic, Tubular P pica (10"')
ETT Electrolytic, 'Tantalum
Ref. Refcrcnce
f farad
Fig. Figure I! micro (10-6)
FT Feed 'Through
" volt
k kilo (103) Var Variable

w watt

TABLE 6. Abbreviations and Symbols.


(Refer to Schematic Diagram 17971D for circuit designations.)


Circuit Mfg. Mfg. Keithley Fig.
Desig. Value Rating TYPO Code Part No. Part No. Ref.

Cl01 500 pf 500 " FT 71590 MFTSOO c15-5OOP 12
Cl02 1.2 Qf 20 " ETT 05397 KlR2J20K C80-1.2M 12
Cl03 4.5-25 pf 500 v CerTr 71590 822AZ C76-4.5/25P 14
Cl04 1.2 pf 20 v ETT 05397 KlR2J2OK C80-1.2M 12
Cl05 1.2 vf 20 " ETT 05397 KlRZJ20K CBO-1.2M 12

Cl06 500 pf 500 v FT 71590 MFTSOO c15-SOOP 12
Cl07 1.2 I.lf 20 v ETT 05397 KlR2J20K C80-1.2M 12
Cl08 1.2 pf 20 v ETT 05397 KlR2J2OK CBO-1.2M 12
Cl09 0.1 pf 50 v MY 84411 601PE C41-O.lM 12
Cl10 1.2 uf 20 v ETT 05397 KlR2J2OK C80-1.2M 12

Cl11 1.2 pf 20 v ETT 05397 KlR2J20K C80-1.2M 12
Cl12 4.5-25 pf 500 v CerTr 71590 822AZ C76-4.5/25P 14
Cl13 0.1 ,if 50 v MY 84411 6OlPE C41-O.lM 12
Cl14 0.1 Llf 50 " MY 84411 6OlPE C41-O.lM 12
Cl15 4.5-25 pf 500 v CerTr 71590 822AZ C76-4.5/25P 14

Cl16 500 pf 500 " FT 71590 MFTSOO c15-SOOP 12
Cl17 4.7 ,lf 20 " ETT 05397 K4R732OK C80-4.7M 12
Cl18 1.5-3 pf 500 " CerTr 71590 822DZ C76-1.5/3P 12
Cl19 10 pf 600 v CerT 71590 TCZ c77-1OP 12
Cl20 10 pf 600 v CerT 71590 TCZ c77-1OP

Cl21 10 pf 600 v CerT 71590 TCZ c77-1OP 12
Cl22 500 pf 500 v FT 71590 MFT500 c15-SOOP 12
Cl23 500 pf 500 v FT 71590 MFT500 c15-SOOP 12
Cl24 500 pf 500 v FT 71590 MFTSOO c15-SOOP 12


Circuit Mfg. Keithley Fig.
Desig. TYPO Number Code Part No. Ref.

DlOl Silicon lN3253 02735 RF-20 14
D102 Silicon lN3253 02735 RF-20 14


Circuit Mfg. Keithley Fig.
Des&. Description Code Part No. Ref.

JlOl Receptacle, n, INPUT, Mil. No. W-680/U (Mfg.
No. 82-811) 02660 cs-95

5102 Receptacle, n, OUTPUT, Mil. No. UG-680/U (Mfg.
No. 82-811) 02660 cs-95

24 0165


Circuit Mfg. Keithlc) Fig.
Desig. Description Code Part No. Ref.
- (F)Plug, n, Mate of .I101 and 5102, Mil. No.
UG-536/U (Mfg. No. 309-34000) 02660 E-96

JlO3 Receptacle, POWER
. Locking Ring (Mfg. No. 126-1430) 02660 ~~-165
. Receptacle (Mfg. No. 126-1429) 02660 (X-163
Body (Mfg. No. 126-1425) 02660 CS-163
- (F)&ug, Mate of J103 (Mfg. No. 126-1427) 02660 CS-162


Circuit Mfg. Mfg. Kcithle) l:ig.
Desig. Value Rating TYPO Code Part No. Part No. Ref.

RlOl 47 kn lO%, l/4 w Comp 44655 RC07 R76-47K 13
R102 50 i: l%, l/8 w MtF 07716 CL% 1~88-49.9 13
R103 47 n lO%, l/4 w Comp 44655 RC07 R76-47 13
R104 470 (1 lO%, l/4 w Comp 01121 CB R76-470 13
R105 2.2 kr? lO%, l/4 w camp 44655 RC07 R76-2.2K 13

R106 2.2 ki? lO%, l/4 w Comp 44655 RC07 R76-2.2K 13
R107 47 i lO%, l/4 w camp 44655 RC07 R76-47 13
R108 47 k!l lO%, l/4 w Comp 44655 RC07 R76-47K 1,
R109 60.4 G l%, l/8 w MtF 07716 CL4 R88-60.4 13
RllO 100 ? l%, l/8 w MtF 07716 CrA R88-100 13

Rlll 1 k?