This classic tube amplifier used to be the best value on the block. Fifteen years ago you could buy one of these for $25. This amp was designed to be inexpensive and to get maximum performance for dollar paid. At the end of it`s sale it sold for about $100 in kit form. David Hafler, the amp designer, made the cost containing compromises in a very
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clever way. For example, the power supply is wimpy by modern standards, but he biased the output tubes into Class A, so the current demands on the power supply are fairly constant regardless of program material. The input section is very simple; an input pentode, followed by a direct coupled split load inverter based on a triode. This topology was very popular at the time, and used the 7199 tube. There is an outer feedback loop that encloses the output transformer and input pentode. There is also a secondary feedback loop that is taken from the ultra-linear screen tap. Even with these two feedback loops, this amplifier very stable. From my measurements and listening tests, I believe that the Dyna ST-70 output transformers are of very good quality (at least the ones on my ST-70). There are many modifications available for this amp. There are two problems that most modifications fall into. First there are the total mods. Basically, everything in the amp is removed except the iron, and the amp is rebuilt. This is all well and good, but don`t forget that this is a budget amp, and the chassis is not so great either. If you are going to dump that much money into a tube amp, why not start with a new chassis, and design it from the ground up instead of making compromises to fit the mod into this chassis. The second type of modification class is just to replace the input board which contains the hard to find 7199 tubes. This can be...
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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