The Comtech has become the de facto standard now for those entering the Amateur TV scene. Sadly the production may be coming to an end with the lower demand for analog tuners and the ICs used becoming obsolete. With the demise of the G1MFG website there is only a limited amount of information about modifying and upgrading these useful workhorses.
Click here to download the full size of the above Circuit.
I have attempted to collect together the most useful information and links to make it easier for you to source the details you need. This is still `work in progress`, more to come. Remember that the Comtec modules have to have correct pre and de- emphasis added, the on-board C/R hf lift filter next to the preset are non standard and should be by-passed. A regular pre-emphasis to CCIR 405 standard should be used. I recommend removing the original filter components on the receiver board and fitting CCIR405 de-emphasis to the receiver but extra gain will be needed afterwards to raise the video level to 1volt pk to drive monitors etc. The original common base addon board used on the MFG boards suffered from field crushing and generally poor sync handling. A revised version using a simple emitter follower instead is shown below and can be fitted onto the original add-on board. There are a few different versions of the board with the latest ones having a dual audio chip and switching regulator IC, but otherwise the layout is very similar. The NE592 is a high gain video amp that was designed for dvd laser output amplification. The built in non-linearity and sharp drop in bandwidth at higher gains means that it is working at full stretch trying to overcome the losses of the de-emphasis circuit. The audio level from the Comtech is rather low for most uses so a simple line amp like this one will give sufficient boost to feed a...
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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