After repairing a couple of Hewlett Packard vacuum tube voltmeters, I read up on some of the company history. I was able to locate a HP-200C oscillator. This HP-200C is very close in design to the company`s initial product. It is a Wien bridge resistance-tuned oscillator with the famous light-bulb stabilized negative feedback circuit designed by W
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iliam Hewlett while doing graduate work at Stanford. (Patent #2268872. Application filed in 1939 and granted in 1942) The original HP-200 was built and sold out of Hewlett`s garage with fellow Stanford grad David Packard, marking the founding of Hewlett-Packard. I did not have a schematic for the 200C but the schematic for the 200I was close enough with nearly identical vacuum tubes (6F6, 6V6, and 6SJ7 for electrically identical 6J7) in the oscillator and amplifier circuits. Output for the 200C is specified as 100 milliwatts, 10 volts into a 1000 ohm load. Although this is labeled an audio oscillator, and it does indeed cover the full audio spectrum, its upper range is well beyond audio, in the VLF radio range at 200 KHz. The HP-200C was in rather rough condition and had not been powered for many years. I used contact cleaner on the range switch and the volume control. The volume control had not tracked properly, but opening it and applying contact cleaner directly solved the problem. The power switch also showed no continuity. Contact cleaner was applied through the bat handle with the switch facing upwards. That cured the switch problem. The power cord was replaced with a new grounded cable. This was followed by a thorough cleaning of the set and checking for safety and a proper level of resistance in the B+ line. The rectifier was pulled out and a variac used to power the set slowly for just the filaments and checking...
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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