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HEWLETT - PACKARD

JOURNAL
TECHNICAL INFORMATION FROM THE -dp- LABORATORIES Vol. 7 No. 6

BLISHED BY THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA FEBRUARY, 1956




Three New -hp- Audio Oscillators

YEAR after year the simple, reliable -hp- ing of the frequency dials. Rotary switches use
R-C audio oscillator remains one of the bar type knobs for ease of switching.
work horses of the electronics laboratory. The /. HIGH-OUTPUT HIGH-QUALITY AUDIO
Hewlett-Packard Company has always taken TEST OSCILLATOR (20 CPS-20 KC)
special pride in the R-C oscilla The new Model 20 1C oscillator at the left in
tor and has always striven to Fig. 1 is designed for testing higher-quality
see that suitable R-C oscillators audio systems. The instrument operates over
are provided for every purpose. the range from 20 cps to 20 kc and provides a
The three oscillators shown in Fig. 1 are evi maximum of 3 watts into a 600-ohm load. Dis
dence of this program. These oscillators are re tortion in the output is less than 0.5% at levels
designs which have been made of three popular below 1 watt and less than 1% at levels up to
-hp- instruments to incorporate in these instru 3 watts.
ments the latest electrical and mechanical fea The output circuit is designed so that the
tures of the -hp- line of oscillators. Electrical instrument can be operated either as a low
features are described in detail below. Mechani source-impedance device or a 600-ohm source-
cally, the instruments are lighter in weight than impedance device. Fig. 2 shows the output cir
their predecessors and are housed in new, cuit arrangement. The output transformer
smaller, more attractive cabinets. The fre feeds through a precision bridged-T attenuator
quency dials are all provided with high-ratio to the output terminals. To permit the instru
rim drives to permit convenient fine-position- ment to be used as a low source- impedance de
vice, the output attenuator is ar
ranged with a zero- attenuation
position in which the attenua
tor is switched completely out
of the circuit. The output term
inals then see the internal impe
dance of the amplifier. This im
pedance is low, in the order of
75 ohms below 5 kc, since a sub
stantial amount of negative
feedback is used in the ampli
fier. When zero output attenu
ation is used, the level of the
Fig. only New -hp- 201 C , 200 J and 202C Audio Oscillators take up only
half the bench space of their predecessors. Two of these oscillators use