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The HP 200 Audio Oscillators Series"From HP Catalog 18A" Laboratory Instruments", Copyrighted 1945."
ADVANTAGES:
RESISTANCE-TUNED PRINCIPLEThere is a sound research story behind this revolutionary -hp- Resistance-tuned Audio Oscillator. Although audio-frequency oscillators have always been standard equipment throughout the communications and electronics fields, there were many "bugs" in types commonly available. These disadvantages included low stability, especially in the lower frequency ranges; need for constant resetting to insure accuracy; low portability, because of the essential weight and bulk of the instrument. So -hp- engineers set out to design and perfect an audio-frequency oscillator which would combine the high stability and very wide range of the coil-condenser type with the flexibility of operation of the beat frequency type. The result is the basically new Resistance-tuned Audio-frequency Oscillator, based on a new fundamental circuit and resulting in new speed and accuracy for electronic tests and measurements. The fundamental resistance-tuned circuit of -hp- Audio Oscillators is shown above. The resonant frequency of this network is inversely proportional to the product of resistance and capacity. Thus the change in resonant frequency of this circuit is three times as great as that of the coil and condenser circuit. A ten to one frequency change is easily possible with the resistance-tuned circuit. The resistance-capacity (frequency determining) network is operated in conjunction with a stabilized amplifier. Positive feedback is applied to this amplifier through the resistance-tuned network, resulting in a very high effective Q for the circuit. See figure 1. Negative feedback is also used, and operates in conjunction with a non-linear resistor to limit amplitude and decrease distortion. It also helps in providing a constant and extremely stable output over the entire range. See figure 2. NO ZERO SETTINGThe excellent physical layout of -hp- Audio Oscillators has much to do with their satisfactory performance. Thermal drift is kept at a minimum by proper placement of components, and by means of low temperature coefficient elements in the resistance network. Furthermore, this thermal drift is not magnified, as is the case with the beat frequency type oscillator. Thus calibration is accurate under all operating conditions, without the inconvenience of constant zero setting, even within the first few minutes of operation. The constant output of these oscillators makes it easy to check the frequency response of the apparatus quickly, easily, accurately. ONLY THREE DIALSThere are only three controls on the panel. They are the main frequency dial which covers a frequency range of 10 to 1; a range switch which selects the desired frequency band, and an amplitude control to vary the output signal level. USES
The primary function of an audio-frequency oscillator is to generate an accurately controlled signal of known frequency. This signal may be used to check the performance of audio amplifiers, broadcast transmitters, and similar equipment. Although applications in the related fields of electronics are of first importance, the usefulness of the -hp- Resistance-tuned Audio Oscillator is by no means limited to the electrical engineering fields. They may be used, for example, to drive mechanical systems, in order to measure resonance and stability. Other measurements of mechanical equipment include measurements of the output frequency of rotating equipment, such as generators and dynamotors. The usefulness of these oscillators is greatly increased because they are small and light in weight; thus easy to carry around. In short, the speed and accuracy of -hp- Resistance-tuned Audio Oscillators make them ideal for an almost endless number of exacting jobs. SPECIFICATIONSSix standard models are available. The Models 200A and 200B have a transformer-coupled output amplifier which will deliver 1 watt into a matched load and are principally designed for use in audio testing. The Models 200C and 200D have a resistance-coupled output amplifier to provide uniform output voltage over their wide frequency range; they are principally useful when handling a wide range of frequencies, where a smaller amount of power is sufficient. Model 202D is a modification of Model 200D, with the frequency range extended down to 2 cycles per second. It is particularly useful where it is necessary to generate an extremely wide range and where low frequencies are involved, as in mechanical vibration problems. The Model 200I is an oscillator of the band spread type. It is intended for interpolation work and for applications where it is necessary that the frequency of oscillation be known very accurately. These oscillators are supplied in a relay rack mounting, as the 200AR, 200BR, 200CR, 200DR, 202DR, and 200IR.
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Average shipping weight 42 lbs.
200B AND 200C Here is the main tuning dial of -hp- Models 200B and 200C Audio Oscillators. Range is 20 cps to 20 kc on 200B, with dial calibrated over approximately 180° and effective scale length of about 20"; 200C has range of 20 cps to 200 kc and effective scale length of about 26".
The -hp- Model 202D is a modification of the 200D, which extends the range down to 2 cps. The tuning dial is calibrated over approximately 300°; the effective scale length is about 75". Before calibration, all -hp- Audio Oscillators are operated for a long period so as to be completely stabilized.
Main tuning dial of -hp- Model 200D is calibrated over approximately 300° and has an effective scale length of about 60". This wide range instrument (from 7 cps to 70 kc) owes much of its speed and accuracy of operation to the precisely calibrated and easily controlled tuning dial pictured above.
Main tuning dial of the 200I, which is an oscillator of the band-spread type, intended for comparison work. The dial is calibrated over approximately 300° with effective scale length about 90" and range of 6 cps to 6 kc. Each Model 200I is carefully hand calibrated to insure maximum accuracy. |
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