It is a resistance tuned oscillator covering from 35 cps (frequency unit was the cycle at this time) to 35, 000 cps in 3 ranges. The major problem with such a resistor / capacitor tuned Bridge is to obtain a constant level output over a full decade frequency range. Bill Hewlett solved the problem by inserting a non-linear element in the feedback loop of the oscillator. This element controls the amount of feedback
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in accordance with the amplitude of oscillation and consequently maintains the proper operating point in the system. And what makes the idea a genius one is that the non-linear element is nothing else than a simple 3 Watts light bulb. As shown in the wiring diagram below, two options with different frequency ranges were available: the 200A and 200B. 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. All other specifications are common for the two units. A two-stage power amplifier with transformer-coupled output delivers 1 Watt into a 500 ohm resistance load. The output voltage is controlled ahead of the output amplifier from a front panel level control. The total harmonic distortion is lower than 0. 5 %. 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. It is so old, they do not even have a HP company logo yet. Units with this particular case style are very rare today. Click on picture or link below for a PDF (2. 5 Mb) of the original instruction manual published in 1943. The manual include schematics, parts list, and chassis layout of the four different models produced by HP in 1943. The HP 200B with rounded corners shown in this photo comes from the Kenneth Kuhn collection. This unit was...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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