Amplification questions....

Gosh .....

That is a interesting question who makes a quailty amp .....?

NOT ALL CB AMPS ARE JUNK NOT ALL HAM ONES ARE GOOD.

A A, AB, B or Class C amp will work on FM/CW just fine but for AM you need to avoid class C.

What would be intresting would be a honest test of a group of them

Here is a place that has some of the HAM ones .... many of them will work on CB ..... but they are not legal since no amp is.

http://www.eham.net/reviews/products/10

 

Maybe this will help. The KL-203 is an AB class.

CLASS "A" operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers in reality are not complementary designs. They are single-ended designs with only one type polarity output devices. They may have "bottom side" transistors but these are operated as fixed current sources, not amplifying devices. Consequently class A is the most inefficient of all power amplifier designs, averaging only around 20% (meaning you draw about 5 times as much power from the source as you deliver to the load!) Thus class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power. The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion. [Much mystique and confusion surrounds the term class A. Many mistakenly think it means circuitry comprised of discrete components (as opposed to integrated circuits). Such is not the case. A great many integrated circuits incorporate class A designs, while just as many discrete component circuits do not use class A designs.

CLASS "B" operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is d ue to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.

CLASS "AB" operation is the intermediate case. Here both devices are allowed to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demand s. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.

CLASS "AB plus B" design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.

CLASS "C" use is restricted to the broadcast industry for radio frequency (RF) transmission. Its operation is characterized by turning on one device at a time for less than one half cycle. In essence, each output device is pulsed-on for some percentage of the half cycle, instead of operating continuously for the entire half cycle. This makes for an extremely efficient design capable of enormous output power. It is the magic of RF tuned circuits (flywheel effect) that overcomes the distortion created by class C pulsed operation.

 

Thanks Big m.

From your explanation can I assume the output stage of a Cobra 29 is class A since it only has a single final?

If you don't care to go through the little (simple?) KL203 schematic with me I understand completely.

You mention that a KL203 is class AB. I see that it has 4 output MOSFETs, two connected in parallel on one side of the primary winding of the output transformer and two in parallel to the other side with full supply voltage to the center tap. The parallel inputs of each two are connected to either side of the secondary of the input transformer, rectified by D3 & D4. Bias is set by C9 and zener DZ1?. Everything to this point is symmetrical.

I assume the first two conduct on the positive half and the second two on the negative half of the input. What I don't understand is the added circuit (biasing?) to the second (bottom) two MOSFETs. Shouldn't the same (or inverted) be applied to the first two? Wouldn't the waveform be skewed on the negative half the way it is? Or am I all wet?

Ted