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Showing posts from March, 2014

Power Supplies

In lesson 48, we examined how power came into your house or plant. It is sent to you in AC form, because it is less expensive, as well as more stable, to send it in a high voltage, low current form, and transform it to lower voltages at higher currents at the point of use.

This is a great way to get power into the homes of everyone on the planet. The big problem comes in that most electronic components don't normally work on AC - they work on DC. So we need some way to convert an Alternating Current power service, into Direct Current for your equipment and devices to run off. Fortunately, this has been taken care of in most of your equipment. Most modern electronics equipment has a power supply built in. That power supply takes the AC line voltage coming into your home, and converts it into the needed DC voltages that your equipment uses.

Transistors

Recall that in a semiconductor diode, we have 2 regions of DOPED semiconductive material. One region is doped positive, and the other region is doped negative. There is also a junction, where the two regions are joined.

When a diode is forward biased, it conducts electricity easily, like a ball rolling down a hill. When it is reverse biased, it is extremely resistive to current flow, as the ball is rolling uphill, and is much harder to get over the hump.

Remember also, that we had diode tubes, which operated in a similar manner. They would conduct electricity in one direction easily, but would not conduct in the opposite direction.

Semiconductors - Diodes and Transistors

But we've already discussed diodes. They are a simple form of vacuum tube aren't they?

Well - yes and no.

While diodes existed in tube form for many years vacuum tube diodes had their problems, and the electronics industry would try to find a way around those problems. Vacuum tube diodes did a fine job of rectifying (turning ac into dc), but they wasted a lot of electrical energy in the process, which made them inefficient and costly to operate. Quite a bit of power was lost just keeping the filament warm! They also had the problem of being physically fragile, and tended to be the main cause of an electrical equipment failure.

As early as 1874, researchers noted that a metal-lead sulfide junction had rectifying properties. They found that it would conduct electrical current in one direction, but if they reversed the current, it would not flow in the opposite direction. This "junction" was "semi-conductive" in nature. They had, withou…

Circuits Circuits Everywhere!

In the last section, we saw how a very simple transmitter worked. It was made up of several different types of electronic components, including capacitors, transistors, resistors, etc. When we assemble several types of electronic components in a configuration that serves some purpose, we call it a CIRCUIT.

Some common electronic components are:
Wire
Resistors
Capacitors
Coils
Transformers
Tubes
Transistors
Diodes

The Triode as Applied to a Circuit

Knowing what a diode is, or how a triode works is of little use unless you have some practical knowledge of how it can be applied within a circuit. We are going to begin with a VERY basic schematic of an early transmitter. Do NOT try to build this at home! It probably won't work, and you may violate Federal Laws ( FCC regulations ) or injure yourself in the process. I will let you know when it is time to begin building projects. ( Yes, this course will come with a practicum ). I will also begin to explain the theory and operation of some new components.

When ever we are looking at a schematic diagram, we must look at it from 2 directions. Top to Bottom, and Left to Right:

First: No circuit can operate without some kind of Power, In this schematic, we have 2 batteries shown operating the circuit.

While it may* be true that electrons flow from negative to positive, it is usually easier to understand movement of voltage through a circuit using the Conv…

A Short Review-earlier lesson

Thomas Edison, famous (at least in America), for inventing the light bulb, See Note 1made many discoveries before he completed his task of lighting the path of the world. Along the way, he incidentally noted that if a filament were energized within a vacuum, that after time, a "shadow" would be left on the inside of the glass, which resembled the shape of the filament. He surmised from this, that within a vacuum, particles (we now call them electrons) were emitted around the wire, forming a cloud, or SPACE CHARGE. This effect became known as the EDISON EFFECT, which is the basic operating theory behind all vacuum tubes. Later, J. Ambrose Fleming invented the FLEMING VALVE, when he noticed that a second ELEMENT, or ELECTRODE within the vacuum along with the filament, but not touching it, electricity would flow through the vacuum and be collected on the second element. The second element was called a PLATE. He further noted that electricity would flow from th…

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.�����…

Vacuum Tubes: A Historical (Hysterical ?) Overview

The vacuum tube, in its very primitive form, evolved from the light bulb. Invented by Thomas A Edison in 1883, the incandescent lamp, had 3 basic necessities to operate:
(refer to fig. 1.1)

The Envelope
The Filament
The Vacuum


figure 1.1

The envelope is basically a sealed container, a box or jar so to speak, which completely surrounds (envelopes) whatever is inside. The first envelopes were made of glass, however, there was no written law that they must be made of glass. In fact, many modern tubes have metal and/or ceramic envelopes.

The filament, otherwise known as the heater, was the basis of the light bulb. The idea was that if a high enough electrical current flows through a coil of wire, it generates light (and heat). Edison's object, was to create a thin enough piece of wire, that even a very low current could generate a great amount of light. The problem was that he kept burning up the filaments. They would work for a matter of seconds, then d…