### Dangerous Curves

As discussed in the previous lesson, a Characteristic Curve is found by applying several different voltage levels, and measuring plate voltages vs. plate current. We note that in a diode, if we go below a certain plate voltage, ( in this case 0 volts ) no plate current flows. The minimum point at which the tube no longer operates is called the CUTOFF POINT . Above a certain plate voltage, additional plate voltage has very little effect in increasing the plate current. The maximum point where raising the plate voltage no longer increases current is called the SATURATION POINT .

In reality, there are two different factors involved in the control of the amplitude ( or level ) of the plate current that flows in a diode. These are the filament voltage ( sometimes called the heater voltage ), and the plate voltage.

Remember that the cathode must be HEATED into thermionic emission. The temperature of the cathode must be high enough to "boil" the electrons from its surface. It stands to reason, that the higher the temperature we heat the cathode to, the more electrons will be "boiled off". Much like raising the temperature of a pan of water causes it to boil away into steam faster.

There does come a point though, where we can boil the electrons off no faster. As we raise the voltage on the heater, it will actually begin to slow down the movement of electrons toward the plate, and begin drawing them toward the heater itself. The underlying reason for this is the space charge itself. As the electrons get boiled off, it causes the overall electrical charge of the cloud of electrons to grow.

At some point, the cloud of electrons reaches a high enough negative charge that it repels any new electrons being boiled off, and they return back to the filament - or have to overcome so much of an opposing force from the cloud that they simply never leave it at all. Therefore, when setting up a tube for operation, you want to make sure that you don't set the filament voltage of the tube so high that it will cause this effect, as it will reduce the efficiency, as well as the life expectancy of the tube. Most tubes are operated at standard values of 6 or 12 Volts.

It is typically considered good practice to begin with a new tube somewhat under that (say 5.0 or 5.5 volts assuming a 6 volt tube) and run it that way until the tube gets older and begins to soften. Often, if a tube gets weak and doesn't output its rated power anymore, you can boost, say a 6 Volt filament to run as high as 7.5 or even 8 Volts. This may extend the life of the tube for a while, but you must watch the plate current. If plate current begins to drop off, then you have the filament voltage set too high. For longest life of a tube, the rule of thumb is to run the tube at the lowest filament voltage that will make the current necessary for proper operation of the device. This maximizes the life expectancy of the tube.

Now the question might arise in one's mind, "Why on earth would someone go through all that effort to keep the \$10 tube of a guitar amplifier a few more months?" The answer is that they wouldn't. However - If we are talking about a \$30,000-\$60,000 final output tube of a broadcast transmitter - the picture changes quite a bit. I've taken tubes that were rated to last 5-7 years, and extended their lives to 10-15 years by this method. And if you can squeeze 3 more years out of a \$60,000 tube... you've saved the company thousands of dollars. Companies tend to be grateful for that and reward you with a higher paycheck.

Assuming that the filament voltage of the tube is set, and that we are running our tube into a fixed resistance load, we can increase the plate current by increasing the plate voltage. Normally when plotting (or drawing) an operational curve for a tube, we assume that the filament is held constant, and the plate voltage is raised. As the plate voltage rises, so does the plate current. We do note, however, that there is a minimum and maximum point, at which the curve is no longer linear ( in a straight line ). We call the minimum point the "lower knee" and the maximum point the "upper knee" of the curve. The saturation point occurs at the beginning of the upper knee, while the cut-off point occurs at the beginning of the lower knee. Under normal conditions, we usually operate the tube within the linear portion of the curve.

Later, we will discuss the characteristic curves of various other components. Each type of component has a slightly different curve, which dictates how the component will operate under different conditions. Understanding these curves will give you a more thorough knowledge of how the component works, and insight as to what it will do when it fails.

### Build a Low Noise And Drift Composite Amp Circuit Diagram

How to Build a Low Noise And Drift Composite Amp Circuit Diagram. This circuit offers the best of both worlds. It can be combined with a low input offset voltage and drift without degrading the overall system`s dynamic performance.
Low Noise And Drift Composite Amp Circuit Diagram

Compared to a standalone FET input operational amplifier, the composite amplifier circuit exhibits a 20-fold improvement in voltage offset and drift. In this circuit arrangement, A1 is a highspeed FET input op amp with a closed-loop gain of 100 (the source impedance was arbitrarily chosen to be 100 kfl). A2 is a Super Beta bipolar input op amp. It has good dc characteristics, biFET-level input bias current, and low noise. A2 monitors the voltage at the input of A1 and injects current to Al`s null pins. This forces A1 to have the input properties of a bipolar amplifier while maintaining its bandwidth and low-input-bias-current noise.

### High Power Output Amplifier TDA7294

The famous SGS-THOMSON ST Microelectronics has introduced a Hi-Fi DMOS high-power amplifier circuit TDA7294, its sound great taste bile, which due to its internal circuit from input to output are field-effect devices, rounded sound Mild, delicate Rounuan.  However, with its assembly amplifier, only TDA7294 single-output power is only 70 W, BTL access law is 100 W from top to bottom, do not feel that power cushion. The author several tests, used to promote TDA7294-level, direct-drive one to four pairs of high-power transistor parallel, the output of strong currents, the power output of 400 W (mono), and the circuit is simple and no need to debug that can reliably work Basically, the IC has maintained a sound and performance.  Ruzuo The figure below shows, R6 for the feedback resistor, the author of the value in debugging 22 k Î© more appropriate, R6 also decided this circuit gain, the gain value will increase.  Quiescent current depends on the power of R7, R8, when its value…

### Full Power Mobile Phone Jammer Circuit Diagram

Full Power Mobile Phone Jammer Circuit Diagram.To day if we are talking about expert Cell phone Jammers we are conversing about this schematic underneath. First off all you should be very very cautious how to use this apparatus. Its completely illegal and so the reason. I post this Circuit is only for educational and testing causes. This type of apparatus is being utilised by security for VIPS, particularly at their limousines to avoid blasting device initiating while the vehicle passes from the goal cell phone-bomb. Off course there are those who use it to make a antic or to make the persons crazy in the rectangle block you are.
The power of the jammer is currently sufficient to do your thing, but certainly you can place a 30W linear power amp at the RF output and impede a much wider locality. So, Be pleasant individual with that and recall that there are people who may need desperately to obtain or make a call and one of them could be you! And if you can't oppose of functioning …