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INSTRUCTION AND OPERATING MANUAL
FOR
AUDIO OSCILLATOR '
1
Serial 30223 and Above B
HEWLETT-PACKARD COMPANY
395 PAGE MILL ROAD, PAL0 ALTO, CALIFORNIA, U . S . A .
1
1 G e n e r a1 D e s c r i p t i o n
I
The Model 200A Audio Oscillator is a general purpose oscillator which
u s e s the resistance-tuned c i r c u i t to generate alternating c u r r e n t voltages f r o m
3 5 to 35,000 cycles/sec.
This audio oscillator provides a s o u r c e of voltage f o r amplifier testing,
audio response &-Ea~smi4&szBc,. lout& speak- resonance t e s t s , and a voltage
s o u r c e f o r bridge m e a s u r e m e n t s .
h
4
i -
INSTRUCTIONS
i MODEL 200A
AUDIO OSCILLATOR
I-.
*--- Sp e c if i c a t i on s
\ Frequency Rating --
k
!
Frequency Range - 35 to 35,000 cycles/sec.
,.
Frequency Dial Calibration - 35 to 350
Range -
xl -
30 350 cycles/sec,
x10 -
350 3500 cycles/sec.
x10 0 3500 - 35,000 cycles/sec,
Calibration Accuracy - k 2%
Frequency Response - +1 db 20 - 15,000 cycles/sec.
Reference: 1000 cycles/sec. 2 2 . 4 volts,
500 ohms r e s i s t i v e load.
Frequency Stability - 2 2% under n o r m a l t e m p e r a t u r e conditions,
including initial w a r m -up
f 10% power line voltage variations change the
frequency Less than k 2% a t 1000 cycles/sec.
P o w e r Output Rating --
-
P o w e r Output 1 watt into r a t e d load ( 2 2 . 4 volts a c r o s s a 500 ohm
load; 50 volts open circuit).
Distortion - L e s s than 1% of r a t e d output f r o m 35 to 15, 000 cycles/sec.
Hum - Less than of m a x i m u m output voltage
Load impedance - 500 ohms ( r e s i s t i v e )
Approximate Internal Impedance -
75 o h m s f r o m 20'to 15,000 cycles/
s e c . Output ungrounded, not balanced to ground.
-1-
P o w e r Supply .-
Rating
P
--
Voltage - 115 volts
Frequency - 50 to 60 cycles/sec.
Wattage - 7 5 watts
Overall Dimensions --
Cabinet Model - 15-1/411 long x 7-1/4" high x 10-5/811 deep
Rack Model - 19" long x T I ' high x 10-3/4" deep
._ -
P a n e l l q r 1long x 7" high
Depth behind panel -
9-1/411
Weight --
-
Cabinet Model 26-1/2 pounds
Rack Model - 26-B/2 Pounds
O p e r a t i n g I n s t r u c biens
Inkpection --
This instrument h a s been thoroughly tested and inspected before being
shipped and is ready f o r u s e when received.
After the i n s t r u m e n t i s unpacked, i t should be carefully inspected f o r any
damage received in t r a n s i t , If any shipping damage i s found, follow the procedure
outlined in the IIClaim f o r Damage in Shipment" page a t the back of this i n s t r u c -
tion book.
c -
.
__ Controls and T e r m i n a l s --
A C P o w e r - This toggle switch, which i s located in the lower left c o r n e r
of the control panel, controls the power supplied to the i n s t r u m e n t f r o m the power
line. When the switch is in the On position, the red indicator will glow,
F u s e - The fuseholder, located on the underside of the c h a s s i s next to
-
the power cablep contains a one a m p e r e c a r t r i d g e fuse.
RANGE - This r o t a r y switch i n s e r t s various range r e s i s t o r s in the f r e -
quency determining c i r c u i t of the o s c i l l a t o r . The position of this switch indi-
c a t e s the multiplying factor f o r the frequency dial calibration.
Frequency Dial - The frequency dial i s calibrated directly in.cycles p e r
sec-nr,d FOP the lowest frequency range.
-2-,
- - to the variable r e sandotherefore the output voltage the the i n s t r u -
AMPL.
voltage admitted
This
amplifier,
i s t r controls the amplitude of
of
oscillator
ment. This control is calibrated frgm " O t t to f t l O O t t in a r b i t r a r y units.
P o w e r Cable - The power cable consists of t h r e e conductors. Two of
these conductors c a r r y power to the instrument while the third conductor
( g r e e n wire) is connected to the i n s t r u m e n t c h a s s i s . The third wire p r o j e c t s
f r o m the cable n e a r the plug end of the cable and m a y be connected to a ground
when i t i s d e s i r a b l e to have a grounded c h a s s i s .
Operqtion --
Connect the power cable of the Model 200A into a 115 volts, 50/60 cycles
p o y e r s o u r c e and turn on the power switch. The i n s t r u m e n t will begin to
operate as soon as the tubes have heated, but f o r m a x i m u m a c c u r a c y a w a r m -
up pe`riod of about 30 minutes is n e c e s s a r y .
S e t the frequency dial and tlRANGE1lswitch: s o that their indications, when
multiplied together, equals the d e s i r e d frequency. F o r example, i f i t i s d e s i r e d
to s e l e c t an output frequency of 8 0 0 cycles p e r second, s e t the frequency dial to
f18011 and the flRANGE1l switch to r r ~ l O f l .
Connect the oscillator output binding p o s t s to the equipment being driven
and adjust the " A M P L . " control f o r the d e s i r e d output voltage.
cr)
N Although the r a t e d load f o r the Model 200A is 500 ohms ( r e s i s t i v e ) , higher
N o r lower impedance loads m a y be used without damage to the i n s t r u m e n t . A
0
rF)
higher impedance load will r e s u l t in l e s s power output and a lower impedance
load w i l l i n c r e a s e the percentage of distortion i n the output voltage.
A s the output voltage of the audio oscillator is reduced, the percentage of
hum voltage will i n c r e a s e , At the lower levels this hum voltage becomes quite
l a r g e , relative to the sine wave output voltage. This undesirable condition can
be remedied by operating the audio oscillator a t o r slightly below r a t e d output
and inserting a suitable attenuator between the oscillator and the equipment being
driven by the oscillator. The voltagg divider c i r c u i t shown below is satisfactory
0 f o r m o s t applications.
1%
I
MODEL 200A EQUIPMENT
OSCILLATOR BEING
SUPPLED
400 ohms
(9
100 ohms
.- 0 -
*
-3-
Other values of r e s i s t a n c e m a y be used to obtain different voltage divi-
sions. In a l l c a s e s , the s u m of the divider r e s i s t o r s m u s t equal the r a t e d load
of 500 ohms. r --
c
Circuit Description
The Model 2 0 0 A Audio Oscillator consists of an oscillator section, an
amplifier section and a power supply.
The oscillator section (tubes V1 and V2) i s a resistance-tuned type c i r -
cuit. Basically, this oscillator is a two-stage r e s i s t a n c e - c o u p l e d amplifier
which i s caused to oscillate by the use of a positive feedback network. T h i s net-
work i s a frequency-selective resistance-capacity combination which controls
the frequency of oscillation, By using a variable tuning capacitor f o r the capa-
city of the network, i t is possible to tune the oscillator over a wide 1 O : l range,
and by using a switching a r r a n g e m e n t to s e l e c t different values of r e s i s t a n c e f o r
the network, s e v e r a l ranges a r e given to the oscillator.
Negative feedback is used in the oscillator section in o r d e r to minimize
distortion and to obtain a very high o r d e r of stability. The amount of negative
feedback, is determined by a r e s i s t a n c e network, one e l e m e n t of which i s non-
l i n e a r (the 3-watt lamp in the cathode of V l ) . This element controls the amount
of feedback in accordance with the amplitude of oscillation and consequently
maintains the amplitude of oscillation substantially constant over a wide f r e -
quency r a n g e . The negative feedback a l s o keeps the operation of the s y s t e m on
the l i n e a r portion of the tube c h a r a c t e r i s t i c . It is notable that the l a m p h a s suffi-
cient t h e r m a l i n e r t i a s o that i t o p e r a t e s well even a t low frequencies.
Following the oscillator is the output amplifier section which includes
tubes V3 and V4. Negative feedback is used in this amplifier in o r d e r to m i n i -
mize distortion and to provide a good frequency response.
The power supply section includes a conventional full-wave r e c t i f i e r
with a low-pass p i f i l t e r f o r removing the ac components f r o m the rectified wave.
-4
Maintenance
Cover and Bottom P l a t e Removal --
The cover i s removed by unscrewing the four s c r e w s which f a s t e n the
cover to the back of the i n s t r u m e n t and sliding the cover toward the rear of the
ins t rume n t
The bcndorn plate is removed by unscrewing the four s c r e w s , one in each
--_ the plate t o the c h a s s i s .
c o r n e r of the battam pta-t+-wkicgfasten ~
-4-
'rube Replacement -- d
.
'd
When replacing any of the tubes except the power r e c t i f i e r , it is d e s i r a b l e
to m e a s u r e the dcstortion in the output if m a x i m u m p e r f o r m a n c e f r o m the i n s t r u -
m e a t ' i s d e s i r e d , bacause a poor tube can 'cause excessive distortion without
seemirigly affecting the operation. The distortion should b e less than 1% of the
rated output with r a t e d load.
I
Replacement of L a m p R7 --
1
The 3-watt lamp R7 is operated at a v e r y low level and should have an al-
- most,infinite life. T h e r e f o r e , the lamp should not be changed indiscriminately.
Howfver, should the l a m p r e q u i r e changing, i t is n e c e s s a r y to check the a c
voltage f r o m the junction of R19 and'C4 to ground with the new l a m p in the c i r c u i t .
As m e a s u r e d with a high-impedance ac vacuum tube voltmeter, this voltage
-
should be within the range of approximately 20 22 volts when the Model 2 0 0 A i s
tuned to 400 cps. If the voltage i s not within this r a n g e p i t m a y be c o r r e c t e d by
adjusting R11.
* If the voltage cannot be brought within the range f r o m 2 0 - 2 2 volts by
means of R11, the new l a m p should b e r e j e c t e d in f a v o r of another,
Inte%mittent Output --
'W , t l J u m p y l l r intermitfent output accompanied by flashing of the 3-watt
o
oscillator l a m p (R7) is a reliable indication of a s h o r t in t r i m m e r capacitor
C1 o r in the f i r s t two sections of the m a i n tuning c a p a c i t o r , If these symptoms
occur, s e a r c h out and c l e a r the s h o r t with a weak a i r j e t o r o t h e r m e a n s . Do
not bend the capacitor plates because bending capacitor plates will d e s t r o y the
frequency calibration
A s h o r t in the back two sections of the m a i n tuning dspacitor o r in
cr).
krimmer C6 will prevent the c i r c u i t f r o m oscillating. Any such s h o r t should
N
N
be cleared as explained above.
0
cr)
Distortion --
Distortion m a y be caused by defective tubes, e l e c t r i c a l leakage in the
coupling capacitors,' defective output t r a n s f o r m e r , defective electrolytic
capacitors, low DC supply voltage, o r excessive output voltage f r o m the o s -
cillator section.
b
4
- Dial Coupler --
0
0
w An insulated coupler connects the m a i n tuning dial to the shaft of the
. main tuning capacitor. If this coupler should become loosened, rotate the capa-
\v cito -ompletely clockwise. T o do this i t will be n e c e s s a r y t o loosen the collar
-5-
of the stop on the r e a r of the panel b e a r i n g . When the capacitor is completely
c h s e d , s e t the main tuning dial s o that the dot to the Left of t 1 3 5 t ton the main 4
tuning dial i s exactly under the hairline. Tighten the coupler with the tuning dial
and tuning capacitor in these relative positions, Then tighten the collar of the
stop s o that the tuning capacitor r o t o r cannot s t r i k e the f r a m e o r s t a t o r a t either
end of i t s a r c .
After the coupler h a s been t i g h t e n e d a n d the dust cover replaced, i t is
desirable to check the calibration of the i n s t r u m e n t .
Frequency Calibration --
If a change o c c u r s in the frequency calibration of this i n s t r u m e n t a f t e r a
long period of use, the cause of this change probably l i e s in the ageing of the
r e s i s t o r s in the frequency-determining network. These r e s i s t o r s have extremely
good stability, however, and the frequency calibration will r e m a i n a c c u r a t e f o r
a v e r y long period of time
, E a c h of the frequency-determining r e s i s t o r s consists of a p r e c i s i o n one-
watt r e s i s t o r in s e r i e s with a one-$half watt r e s i s t o r . The l a t t e r is s e l e c t e d to
give the instrument a v e r y a c c u r a t e f-requency calibration. T h e r e f o r e , adjusting
the frequency calibration r e q u i r e s that the value of these s m a l l r e s i s t o r s be
changed a s n e c e s s a r y to obtain p r o p e r calibration.
I
An oscilloscope, an a c vacuum tube voltmeter, and a secondary f r e -
quency s t a n d a r d a r e needed to adjust the calibration of the Model 200A. The
secondary standard should have sinusoidal output and should provide frequencies
of a t l e a s t 1 kc and 10 k c . Before recalibrating, allow the Model 200A to h e a t
foi. thirty minutes o r m o r e , Then connect the Mo*del 200A to the v e r t i c a l deflec-
ting-plate input of the oscilloskope and the secondary frequency s t a n d a r d to the
horizontal deflecting-plate input.
Next, check the calibration of the Model 2 0 0 A by m e a n s of L i s s a j o u s
figures on the oscilloscope, determining whether the frequencies generated by
the M.odel 200A a r e in g e n e r a l higher o r lower than the dial calibration. When
making this check, i t i s n e c e s s a r y that the dust cover be tightly on the i n s t r u -
m e n t a s the frequency calibration will change when the dust cover i s loose o r
off the instrument.
If the instrument is in need of recalibration, the dial calibration will
show a definite trend of e r r o r - e i t h e r higher o r lower. than the t r u e output f r e -
quency f o r each range. The various ranges of the i n s t r u m e n t do not n e c e s s a r i l y
change in the s a m e "directionI1.
If the xl range r e q u i r e s readjusting, change the small r e s i s t o r s R1A and
R4A. If the ouput frequency is higher than the dial calibration, i n c r e a s e the
-6-
value of the small r e s i s t o r s ; if the.output frequency is lower than the dial cali-
bration, d e c r e a s e the value of the small r e s i s t o r . A change of about 5 0 , 0 0 0
ohms will change the calibration about 1/2%Q Do not change the value of Rl and
R1A m o r e than 50,000 o h m s without making a corresponding change in R 4 and
R4A because i t i s n e c e s s a r y to keep the values of each s e t of range r e s i s t o r s as
equal a s possible. Unbalance in t h e - r e s i s t o r s will tend to cause the oscillator to
be unstable. After each change i t i s n e c e s s a r y to replace the dust cover s e c u r e l y
before checking the output frequency.
The s a m e procedure should be u s e d i f i t is n e c e s s a r y to adjust the cali-
bration of the other r a n g e s . On the x10 range a change g r e a t e r than 5 , 0 0 0 ohms
should not be made in R2 and R%Awithout a l s o changing R 5 and R 5 A , On the xl00
range a change g r e a t e r than 500 ohms should not be m a d e in R3 and R3A without
changing R6 and R6A.
It is important that the dust cover be tightly in place a f t e r each adjustment,
because the frequency calibration i s affected by the position of the dust cover.
If any considerable amount of change in the r e s i s t o r s i s n e c e s s a r y g i t m a y
be desirable to replace the e n t i r e range switch a s s e m b l y . These a s s e m b l i e s a r e
available f r o m the Hewlett-Packard Company.
The vacuum tube voltmeter should be u s e d to ch'eck the output f r o m the
instrument a f t e r the recalibration h a s been completed, . S e t the m a i n frequency dial
of the Model 200A to ft10OT1 and the AMPL. control to about t18011 r m o r e . Connect
o
+he VTVM to the output t e r m i n a l s and m e a s u r e the output of each range. If the
range switch r e s i s t o r s have been properly adjusted, the difference between the
obtput of the ranges with the dial s e t a t t l l O O t l should be within 1 db (approximately
preferably l e s s . If the difference in output is g r e a t e r than 1 db, the usual
12'%)o),
cause i s that the frequency determining r e 9 i s t o r s f o r the range in question a r e
not properly balanced,
T r i m m e r Capacitors --
Two t r i m m e r c a p a c i t o r s a r e provided f o r the m a i n tuning capacitor.
These t r i m m e r s a r e adjusted a t the factory and do not r e q u i r e f u r t h e r adjust-
m e n t f o r the life of the equipment. If 'the t r i m m e r s inadvertently should b e -
come misadjusted, directions f o r resekting should be requested of the Hewlett-
P a c k a r d Company.
-7-
Trouble Shooting --
The fallawing i a listing of possible symptoms.,
s c a u s e s s and r e m e d i e s .
Syxnp t om a Caases Remedies
Instrument inoperative Blown fuse C l e a r s h o r t c i r c u i t and
(Indicator l a m p won't replace fuse ~
light, no audio output) /si
Instrument inoperative Defective tube Replace tube ( s e e "Tube
(Indicator l a m p lights, Check the 5V4 Replacement" in Main-
?
no audio output) tube first tenan ce section)
S h o r t c i r c u i t in DC Replace capacitor
power c i r c u i t capa-
citor
S h o r t c i r c u i t in C2 C l e a r the s h o r t c i r c u i t
(two r e a r sections) as outlined i n the "In-
o r C6 t e r m i t t e n t Outputrt p a r a -
g r a p h in the Maintenance
section.
Xnt e r m i tt e nt Output Capacitors C4 o r Replace capacitor
C5 intermittently
open.
Short c i r c u i t i n C2 C l e a r the s h o r t c i r c u i t
(two f r o n t sections) as outlined in the !'In-
o r C1 te r m i ttent Output" p a r a -
graph in the Maintenance
section
-8-
++
-+
1
lo
+ABLE OF REPLACEABLE PARTS
C ir cui t
*
Description Mfr.& M f r s .
Ref. Designation
c1 Capacitor: v a r i a b l e , a i r , 100 ullf 12 -11 AA, A-103L
c2 Capacitor: v a r i a b l e , air 12 - 5 HP
530 Buf p e r s e c t .
c3 Capacitor: fixed, p a p e r 16-5 A
5 uf; 600 vdcw Type 684
c4 Capacitor: fixed, p a p e r 17 -44 P
4 , 4 uf; 600 vdcw P 8 -8
c5 Capacitor: fixed, p a p e r , 16-1 A
Type P 6 8 8
. 1 uf, 600 vdcw
C6 Capacitor: v a r i a b l e , air, 12 -11 AA
100 W1.f A-103L
c7 Capacitor: E l e c t r i c a l value adjusted
a t factory
C8 Capacitor: fixed, p a p e r 16-22 A
2000 wfp -25% t 50% 600 vdcw Type 684
c9 ABC Capacitor : fixed, e l e c t r o l y t i c , 18-31 X
10,10,10, u f ; 450 vdcw FPT-389
c10 Capacitor: fixed, p a p e r , 17-3 P
4 uf, 800 vdcw P8-4
c11 Capacitor: fixed, e l e c t r o l y t i c 18-40 X
40 uf, 450 vdcw FPS -146
c12 Capacitor: fixed, m i c a 14-17 V
27 uwf; _+lo% 500 vdcw Type OXM
C13, C15 E l e c t r i c a l value adjusted a t f a c t o r y
C14 Capacitor: fixed, e l e c t r o l y t i c 18-50 X
50 uf, 50 vdcw TC-39
E l e c t r i c a l value adjusted a t the f a c t u'
C16 Capacitor: fixed, e l e c t r olyti c 18-12 Z
40 uf, 450 vdcw MT 4540
*See " L i s t of M a n u f a c t u r e r s Code L e t t e r s F o r Replaceable P a r t s Table.
-9 -
TABLE OF REPLACEABLE PARTS w
C i r cui t Description -hp - Mfr. & Mfre.
Ref. Stock No.
Rl-R6 P a r t of Range Switch Assembly
R7 L a m p : 3-watts; 1120 V 219-4 0
R8 R e s i s t o r : fixed, composition 24-47K B
47,000 o h m s ; -+lo%, 1 W GB 4731
R9 R e s i s t o r : fixed, cornposition 25-100K B
100,000 ohms; 2 W HB 1041
R10 R e s i s t o r : fixed, composition 24-100K B
1100, 000 o h m s ; + l O b / ~ ~ W
1 GB IO41
R11 R e s i s t o r : variable wirewound, -
210 5 G
1000 o h m s ; l i n e a r t a p e r 21-010-355
R12 R e s i s t o r : fixed, wirewound 26-3000 R
3000 o h m s ; L.lO%, 1 W Type B W
R13 R e si s t o r : fixe d, composition 24-560K B
560,000 ohms, &BO%, 1 W GB 5641
1114 R e s i s t o r : fixed, composition 25-820 B
820 o h m s ; +IO%, 2 W HB 8211
R15 R e s i s t o r : fixed, wirewound 26-11 S
25, 000 ohms; +PO%, 10 W Type 1-3/4E
R16 R e s i s t o r : fixed, wirewound 26-10 S
1 0 , 0 0 0 ohms; +lo%, 10 W Type 1-3/4E
R17 R e s i s t o r : fixed, wirewound 27-4 s
10,000 ohms; +IO%, 20 W Type 2R
R18 R e s i s t o r : v a r i a b l e , composition 210 -54 B
25,000 o h m s ; l i n e a r t a p e r JU 2531
R19 R e s i s t o r : fixed, composition 24-15K B
15K ohms; +lo%, B W GB 1531
R20 Re si s t o r : fixed, composi ti on 24-3300 B
3300 ohms; +lo%, 1 W GB 3321
RZ1 R e si s to r : fixed, composition 24-56K B
56,000 ohms; +lo%, 1 W GB 5631
-10-
TABLE OF REPLACEABLE PARTS
~~
Circuit Description -hp - M f r . & Mfrrr.
Ref. Stock No. De signation
R22 R e s i s t o r : fixed, composition 24-560K B
560,000 ohms; +lo%, 1 W GB 5641
R2 3 R e s i s t o r : fixed, composition 24-56K B
56,000 ohms; 21070, 1 W GB 563E
E l e c t r i c a l value adjusted at f a c t o r y
R24 R e s i s t o r : fixed, composition 25-820 B
820 ohms; +lo%, 2 W HB 8211
R2 5 R e s i s t o r : fixed, composition 24-10K B
1 0 , 0 0 0 ohms; +YO%, 1 W GB $031
R26 R e s i s t o r : fixed, composition 24-10K B
1 0 , 0 0 0 ohms; +lo%, 1 W GB 1031
R2 7 This c i r c u i t r e f e r e n c e not a s s i g n e d
R28 R e s i s t o r : fixed, composition 24-33 B
33 ohms; +lo%, 1 W GB 3301
R29 R e s i s t o r : fixed, composition 24-220K B
220,000 ohms, +lo%, 1 W GB 2241
R30 R e s i s t o r : fixed, composition 24-220K B
220,000 ohms, +1070, 1 W GB 2241
Binding P o s t : 312 -3 HP
FI F u s e : 1A; 3AG 211-1 T, 312001
Fuseholde r : 312 - 7 T, 351011
P o w e r Cable: 812-56 HP
Knob: 3" d i a m . 37 -14 HP
Knob: 1-I/2l1 d i a m , 37-18 HP
I1 Lamp: 211-47 0 , #47
Indicator Light: 312 -10 BB, 807BS
-11-
?'ABLE OF REPLACEABLE PARTS
C i r cui t De s c ripti on -hp- Mfr.t Mfrr.
Ref. Stock No. Designation
L1 R e a c t o r : 6 H @ M A ; 240 o h m s
I
125 919-4 HP
Coupling Assembly: M -2 5B HP
P a n e l B e a r i n g Assembly: M-67 HP
S1, R l - R ' Range Switch Assembly: A-E9W HP
s2 Toggle Switch: 310 -11 Dq
, 20994-HW
T1 Output T r a n sf o r m e r : 912 -3 HP
T2 Power Transformer: 910 3
~~
HP
v1 Tube: 657 212, -6J7 ZZ
v2 Tube: 6 F 6 212-6F6 zz
v3 Tube: 6F5 212-6F5 zz
v4 Tube: 6V6 -
212 6V6 zz
v5 Tube: 5V4 212 - 5V4 zz
c
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