Last, but not least, the 200CD was the last fully vacuum tube instrument produced by HP.
#Audio tuner bill full
It remained in the Hewlett-Packard Test and Measurement catalog until 1985, a full 33 years which is rare in the electronics industry. The HP200CD was a serious competitor in the HP longest product life contest. 160 mW into 600 ohms or 20 Volts open circuit at 1 % distortion and +/- 1 dB frequency response. The HP 200CD has the following specifications in the 1952 catalog page 9: Frequency coverage 5 cps to 600 Kc in 5 ranges. They tried it, and it worked, to 600 Kc, the first of hundreds of contributions that Barney would make to this Company, over a 40 year career." His first look at the circuit of the HP 200 convinced him that simply by going to a balanced circuit configuration, he could get well-over a 10 to 1 improvement in the frequency coverage. John Minck, in his "Inside HP Narrative" tells the story as follows: "Barney had a way of looking at problems that was unique. He was recruited to join HP in the late 1940s. Barney was a classmate of Bill and Dave at Stanford, and was employed by Bell Telephone Labs. In 1952 Barney Oliver did a complete redesign of Bill's basic oscillator to raise the upper frequency limit to 600 Kc. Combining different tools in a single unit results in many advantages for instruments of this era where temperature drift and component aging were significant sources of measurement uncertainty. This is the first example of an HP product that provides answers to multiple problems found in production testing. The control part of the 205AG integrates two vacuum tube voltmeters, one to measure the input and the second to measure the output of the device under test. The 205AG brought the output level to 5 Watts into an external load of 50, 200, 500 or 5000 ohms with a distortion of less than 1 % from 20 cps to 20,000 cps.Īnother innovation is that the 205AG integrates six basic instruments in the same box to make amplifier or network, loss / gain measurements.Īs shown in the block diagram below the signal source is the model 200B basic circuitry followed by a 5 Watt (2 x 6L6 tubes), push-pull amplifier whose output is applied to the network under test through a 110 dB, 1 dB step attenuator and a line matching transformer. Units with this particular case style are very rare today. It is so old, they do not even have a HP company logo yet. The HP 200B with rounded corners shown in this photo was hand built, probably in the second garage ( 481 Page Mill Road ) in 1940, and may have been handled by Bill and Dave themselves. The total harmonic distortion is lower than 0.5 %. The output voltage is controlled ahead of the output amplifier from a front panel level control. A two-stage power amplifier with transformer-coupled output delivers 1 Watt into a 500 ohm resistance load. A small modification of 6 resistors values resulted in different frequency ranges 35 to 35,000 cps for the 200A and 20 to 20,000 cps for the 200B.Īll other specifications are common for the two units. Bill's prototype became the HP company's first product the HP 200A.Īs shown in the wiring diagram below, two options with different frequency ranges were available: the 200A and 200B.