HP 650A - in its original wood box One of the oldest showpiece of the collection

The first Test Oscillator

Modification of the original audio oscillators produced many signal sources with applications other than the audio frequency spectrum.

The 650A Test Oscillator was the first example which appeared in the 19-A, 1948 catalog. It covers from 10 cps to 10 Mc in six bands with a 15 milliwatts output level into 600 ohm, a +/- 1 dB flatness and better than 5 % distortion at 10 Megacycles.

It was the first HP instrument to bring audio frequency speed, accuracy and ease of operation to higher frequencies and to enable a wide variety of measurements in supersonic, video and RF bands. This would answer the needs of fast growing new industries like television wide band systems and telephone carrier measurements. The 650A can be considered as HP's first instrument in the telephone industry, a business which became an HP division some years later.

The HP 210A

First Square Wave Generator

The 210A was another signal source introduced in the 1943 catalog.

The 210A can be considered as the first HP pulse generator. Working from 20 cps to 100 Kc it can deliver up to 50 volts peak to peak with a 1 microsecond rise time for testing receivers, video amplifiers, networks and transmitters or to measure electronic circuitry time constant.

The 210A is not a self contained generator but rather a clipping amplifier which needs a sine wave input from an external generator.

The first pulse generator to include the signal source was the 212A introduced in the 1950 catalog (20-A) on page 28 which is shown below.

HP 211A

The HP 211A Square Wave Generator

The last evolution in the 50s of the signal sources product line would be the 211A square wave generator introduced in the Hewlett-Packard Journal, May, 1955, volume 6, number 9.

Main specifications were: Continuous frequency coverage from 1 cps to 1 mc. Output 7 Volts across 75 ohms or 55 Volts peak-to-peak across 600 ohms with a rise time of 20 millimicroseconds (as noted in the specifications listing - Rise time value expressed in nanoseconds was not yet a current practice in 1954)