AMPLIFIER CLASSIFICATION

[Sonar]

I did some online research about amplifiers and their classifications.
It was all Greek to me.
A, AB 1, C ETC ETC. My interest is with older tube cb amps. Palomar, d&a, pride, varmint etc etc.
I'm assuming these types of tube amps fall in the same class or do they?
What is it that makes an amp A, C AB1 etc etc, and how important is this for mode of operation (SSB FM CW AM?) Thanks. 73

 

[Robb]

Biasing circuit; configuration and regulation.

 

[Sonar]

Biasing.

Robb. Is is possible to explain in layman's terms what Biasing is?
I did some research but all I've read was written with the idea that the people reading were technically versed. I'm obviously not and am assuming there's a formula that can explain it in a simplified manner. Thanks

 

[FredTx63]

Hey Sonar check your PM!

 

[Robb]

In simple terms, it means to control the voltage/current flow for switching the amp device. Linear amps will have regulation to the flow to to keep the output gain uniform. Most CB amps are not linear, they do not regulate this flow. Not easy for me to define, as I am still learning about it myself.

From Wiki:
Biasing in electronics means establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components. Many electronic devices such as transistors and vacuum tubes, whose function is processing time-varying (AC) signals also require a steady (DC) current or voltage to operate correctly — a bias.

 

[Tallman]

Think of the tubes as VALVES. The bias controls how far the valve can open when driven with a signal. Class "A" is full reproduction and the least efficient. What ever you put in is amplified in full, in short 360 degrees of conduction.
Class AB1 conducts for more than 180 up to about 270 degrees and uses a pair of tubes or transistors with transformers to produce the signal. Each tube or transistor sort of overlaps and you get better than class "A" performance with the added benefit of harmonic cancellation.
Class "C" is the most efficient analog amplifier. Splatters like crazy and sounds like hell on ssb.
Class "D" is the most complex(Digital) in which you take the signal and break it down in slices by sampling it at a high rate. Very interesting method of signal amplification and conditioning. It uses analog to digital circuits to convert analog signal into data.

 

[fourstringburn]

Class "D" is the most complex(Digital)

Sorry, but that is a common misconception that the "D" in class D amplifiers stands for digital. It's just another letter used down the line to classify amps. The A or B letters don't stand for anything either. It wouldn't surprise me if the big amp CBers think the "C" in class C amps stands for competition. After all, they are referred to as competition amps!

Class D amps are being common place for solid state Bass guitar and PA amplifiers in the music world. These are lightweight amps, highly efficient,
especially at high power ratings. I should know, I use them for my Bass guitar amps myself.

Without getting into the geek side of these types of amps they are based off pulse width modulation. There is plenty of info online too learn about these amps if some one wishes too. It's not likely these will find their way into voice communication anytime soon.

There are also class H audio amps and I'm sure that doesn't stand for heavy duty.

 

[Tallman]

Yeah I forgot about the class "H" amps. The class "D" design I was talking about came from Harris Semiconductor as a teaching tools for the technicians.
It did use the Analogue to Digital Chip So I don't see why it would not be "Digital". I guess the digital was a vernacular used because of the pwm chip.
Those class "H" amps were a bear to get properly balanced.

http://www.audioholics.com/audio-amplifier/amplifier-classes

 

[Captain Kilowatt]

Robb. Is is possible to explain in layman's terms what Biasing is?
I did some research but all I've read was written with the idea that the people reading were technically versed. I'm obviously not and am assuming there's a formula that can explain it in a simplified manner. Thanks

Think of it this way. A transistor (or tube) requires a certain input voltage to cause it to conduct. Without the proper driving voltage a transistor will not conduct until the driving power is high enough to force the device conduct on it's own. Bias is a fixed DC voltage applied to the transistor base below the turn-on limit so it does not conduct until drive is applied. When drive is applied that voltage adds to the fixed DC voltage causing the transistor to conduct much sooner than it would without the bias voltage. This is how the device is able to conduct only during various parts of the RF cycle......by varying the amount of applied fixed DC voltage. In the case of a class A amp the bias is enough to switch the device on even without drive and in the case of class C there is no voltage applied and the driving power must be high enough to switch it on by itself. this is why a class C amp only conducts over a small portion of the RF cycle because it is only near the peaks of the cycle that the driving power is sufficient to cause it to conduct. Class AB and class B are somewhere in between. That's about as simple as I can explain it.

 

[BBB]

Hams dabbling in Class E amps for AM use:

http://www.classeradio.com/

 

[Sonar]

Think of it this way. A transistor (or tube) requires a certain input voltage to cause it to conduct. Without the proper driving voltage a transistor will not conduct until the driving power is high enough to force the device conduct on it's own. Bias is a fixed DC voltage applied to the transistor base below the turn-on limit so it does not conduct until drive is applied. When drive is applied that voltage adds to the fixed DC voltage causing the transistor to conduct much sooner than it would without the bias voltage. This is how the device is able to conduct only during various parts of the RF cycle......by varying the amount of applied fixed DC voltage. In the case of a class A amp the bias is enough to switch the device on even without drive and in the case of class C there is no voltage applied and the driving power must be high enough to switch it on by itself. this is why a class C amp only conducts over a small portion of the RF cycle because it is only near the peaks of the cycle that the driving power is sufficient to cause it to conduct. Class AB and class B are somewhere in between. That's about as simple as I can explain it.

Excellent explanation. I absolutely understand now. Thanks. 73