Here is the schematic from the Eico 667 tube tester. It is very similar to the 666, except now there are a pair of extra levers, and a few test sockets are missing. But the meat and potatoes are identical. If you are planning to restore your 667 to peak operating condition, here are a few pointers. Replace the selenium diodes CR1 and CR2. I rivet
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in a small terminal strip, using the mounting hole from the `old` diodes. It is now easy enough to install 1N4007 diodes across the terminal strip. While you are at it, replace filter capacitors C1 and C2. Since modern-day capacitors are much smaller than their ancestors, I replace C1 with a 22uF/150VDC or possibly a 47uF/150VDC capacitor, while C2 is now a 22uF/25VDC capacitor. Typically I use whatever I happen to have on hand. Carefully check the calibration potentiometers R7 and R18. If you are having any difficulties calibrating your tester, change these potentiometers! Replace them with any quality 100K linear-taper potentiometer. I make sure I use a control with a nylon shaft, and avoid those with split and/or splined shafts. If necessary, I also cut a notch in the top of the shaft, to facilitate using a small screwdriver for any adjustments. Eico used very poor quality controls here, and they are prone to failure. When doing the calibrating for the Line Adjust, I will set it so `High Noon` gives me a reading of 6. 3VAC with a 6L6 inserted in the socket! This may seem obvious, but I sometimes carefully calibrate the Line Adjust exactly as the manual describes, and I end up testing a 6L6 with barely 6VAC on the filaments. I choose a 6L6 as opposed to a 6V6 because the filament draw is higher, and I want to be sure this procedure is done under a decent sized load! You can measure the filament voltage while testing say 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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