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hewlett-pa: 330B; Distortion Analyzer

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » hewlett-pa: 330B; Distortion Analyzer
Pius Steiner
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23.Sep.12 11:10

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"From HP Catalog 18A" Laboratory Instruments", Copyrighted 1945."


Covers audio spectrum
Measures noise as small as 100 microvolts
Linear r-f detector
Terminals for oscilloscope
Ball bearing frequency control dial
High order of accuracy and stability

Measuring total distortion of audio signal
Measuring total distortion of audio-modulated r-f carrier
Measuring voltage level, power output, amplifier gain
Measuring noise and hum level of audio frequency equipment directly Determining frequency of unknown audio signal
High-gain, wide-band, stabilized amplifier

The Model 330B Distortion Analyzer is Hewlett-Packard's newest and finest distortion measuring instrument. The Model 330B is capable of measuring distortion at any frequency between 20 cps and 20,000 cps. It will make noise measurements of voltages as small as 100 microvolts. A linear r-f detector makes it possible to measure these characteristics directly from a modulated r-f carrier. The convenience of operation, high sensitivity, accuracy, stability, and light weight of the 330B make it a uniquely valuable instrument for broadcast, laboratory, and production measurements.

The circuit of Model 330B consists of a linear r-f detector, a frequency-selective amplifier, a vacuum-tube voltmeter, and a regulated power supply.

The r-f detector includes a diode rectifier operating in conjunction with a resonant circuit which is tuned to the carrier frequency under measurement. The detector covers a range of 500 kc to 60 mc and is varied by means of a tuning condenser and range switch which selects one of six bands. The detector may be switched out of the circuit when audio frequencies are used.

The 20 db amplifier operates in conjunction with the -hp- resistance-tuned circuit to provide infinite attenuation at one frequency while allowing all other frequencies to be passed at the normal gain of the amplifier. See figure 1. Negative feedback is employed in the amplifier to minimize distortion, give a uniform response over a wide range of frequencies, and to provide a high order of stability. The frequency response is from 10 cps to 100,000 cps; thus even the fifth harmonic of 20 kc is passed through the amplifier without attenuation.

The voltmeter section of the instrument consists of a two-stage high-gain amplifier, a rectifier, and an indicating meter. A large amount of negative feedback is employed to insure stability and a uniform response from 10 cps to 100,000 cps.

Typical Applications

The flexibility of-hp-'s Model 330B leads to a number of applications. It may be used to measure the total distortion at any frequency of an audio signal, or of an audio-modulated r-f carrier. It may also be used as a voltmeter for measuring voltage level, power output, amplifier gain, and for any other use which a high-impedance, wide frequency range, high sensitivity voltmeter is desirable. With the added gain of the amplifier the vacuum-tube voltmeter has sufficient sensitivity to measure directly noise and hum level in audio frequency equipment, such as studio amplifiers. With the linear detector the noise level in the carrier output of transmitting equipment can be readily measured. The frequency selective amplifier can be used as an audio frequency meter to determine the frequency of an unknown audio signal. The instrument may also be used as a high-gain, wide-band, stabilized amplifier, having a maximum gain of 75 db.

This new Model 330B Distortion Analyzer is particularly adapted for use as an all-around measurement device in the broadcast studio and broadcast transmitter rooms. Ruggedness, high stability, and the easy operation of the ball-bearing frequency control dial are features which add to its convenience and reliability for production test jobs.



Range: The Model 330B will measure distortion at any frequency from 20 cps to 20,000 cps. The frequency of measurement is selected with a directly calibrated dial having its lowest range calibrated directly in cycles per second. A range switch selects the operating band.

Accuracy: The circuit will eliminate the fundamental by more than 60 db and will attenuate the second harmonic and higher harmonics by less than 10%. Distortion measurements accurate within ±3%, for distortion levels as low as 0.5%.

Sensitivity: Distortion levels of 0.3% are measured with full scale, and levels of 0.1% can be read with good accuracy at approximately 25% scale reading.

Voltmeter Range: Nine ranges are provided with full-scale sensitivities of .03, .1, .3, 1.0, 3.0, 10, 30, 100, 300. A calibration from +2 to -12 db is also provided, and the ranges are related to each other in 10 db steps. The range switch indicates db level as well as voltage range. Zero level is 1 milliwatt in 600 ohms.

Voltmeter Accuracy: The voltmeter accuracy is ±3%. The accuracy is not affected by changing of tubes or by line voltage variations from 105 to 125 volts. The indicating meter is a 4-inch square type with large, easily read scales.

Voltmeter Frequency Response: The frequency response of the vacuum tube voltmeter including the analyzer circuits is flat within 3% over the range of 10 to 100,000 cps.

Noise Measurement: When used to measure hum or noise the meter will give a full scale deflection on a signal of 300 microvolts. Satisfactory readings may be made to 80 db below 1 milliwatt in 600 ohms.

R. F. Detector: A linear R. F. detector is provided to rectify the transmitted carrier. The input circuits of this rectifier are tunable from 500 kc to 60 mc, in 5 bands.

A. F. Input Impedance: The input impedance at the audio frequency input terminals is approximately 200,000 ohms shunted by 24 mmf. The input impedance at the vacuum tube voltmeter terminals is 1 megohm shunted by 32 mmf.

Oscilloscope Terminals: Terminals are provided for connection to an oscilloscope to observe the wave shapes of the original signal and the residual distortion components. The maximum gain from the A. F. input to the oscilloscope terminals is 75 db.

Power Supply: The instrument operates on 115 volt 50/ 60 cycles. The power consumption is 90 watts. An electronic voltage regulator maintains a constant plate supply.

Mounting: The instrument is mounted in an attractive oak cabinet. Front panel size: 19 inches x 10 ½ inches, depth 13 inches. The panel is finished in wrinkle grey. The Model 330B can be supplied for rack mounting and when so supplied is designated by the Model No. 330BR.

Net Weight 50 lbs. Shipping Weight 120 lbs.

This article was edited 25.Sep.12 12:12 by Pius Steiner .