Some months ago a surprise package turned up in my mailbox. Ananonymous donor had sent me threewonderful, old germanium transistors. The2N170 and a pair of 2N107`s (all date-coded December 1956) werestill in theiroriginal plastic tube packaging. Athin booklet, Type 2N107 Transistor Circuits for Experimenters [and] Amateurs, was also included. Thecir
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cuits shown in the booklet appear to be aimed at the rank beginner:audio amplifiers, code practice oscillators and the like. However, the "SimpleRadioReceiver" caughtmy eye (lower right-hand corner below). This was exactly the sort of project that captivated me in my early youth. Growing up inSt. Louis, Missouri in the late 1960`s, Ienjoyed listening to baseball and ice hockey games on KMOX, and pop music on KXOK, using a wide variety ofsimplehomemade AM radio receivers. Although there`s nothing much ofinterest to me on the broadcast AM radio dial these days, Ihave a nostaligia forthe simple circuits thatmarked my first stepsin amateur radio. By the way, this same circuit also appeared in the first (1957) through the seventh (1964) editions of the General Electric Transistor Manual. While I`m not now interested in listening to broadcast AM radio, a direct-conversion receiver suitable for copying CW only requires the addition of a beat-frequency oscillator (BFO) to the above receiver circuit. With sufficient BFO drivethegermanium diodecan be made to function as acommutating (switching) mixer. On the other hand, a single diodemixerhas several notable disadvantages; perhaps the worstis therelative lack ofAM signal rejection. This type of mixer alsocreates more spuriousfrequency energy and the port-to-port isolation isquite inferior as compared to more advanced designs. Nevertheless, the more I thought about it the keener I...
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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