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don
| | Posted on Thursday, January 17, 2002 - 10:16 am: | 
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What is the difference between the AB class and C class amps? Is one beter for SSB than the other? What class are the KL amps and also the Palomar amps?
Thanks |
Mr_Rf
| | Posted on Friday, January 18, 2002 - 2:12 am: |
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THe "Class" of amplifier refers to how the amplifier handles different types of signals (AM, FM, SSB, etc).
In terms as close as possible to layman terms, the "Class" designator defines how much of one AC cycle of the input signal is being amplified. Your radio signal is an "AC" voltage just like the AC which comes out of the wall sockets in your home...but at a lot higher frequency. The frequency, or cycle, (ex. 60 Hertz, or 60 cycles...both the same) refers to how many times the voltage coming out of your wall socket, or antenna in the case of a radio, turns on and back off (ie. Alternating Current or "AC") during a 1 second period of time.
If an amplifier is a "Class A" amplifier that means it can amplify the whole part of the cycle of a pure AC sinewave signal. (pure...means that the voltage steadily rises and falls at a smooth, consistant rate) The higher the Class Letter (ex. AB, B, C, D, E, etc.) the lesser the portion of the sine wave that is amplified. A Class A amplifier amplifies 100% of the cycle time. A class C amplifier only amplifies only about 33% of the cycle of the AC signal it is amplifing. That means that 67% of the time that the sinewave signal is actually on is not being amplified (pretty crummy...ugh).
For "Amplitude Modulated" (AM) signals that change the level of the signal to produce audio a greater precentage of the carrier must be amplified otherwise the signal would sound very distorted and cause great ammounts of interference to many other frequencies, both in the CB band and outside the CB band (harmonics).
Nutshell...
Class C amps will NOT work for AM/SSB CB radios. Class C amps are for FM transmittes like hams use above 29.5 MHz (6 meters, 2 meters, etc.)
Class AB is a more efficient type of Class A amplifier that WILL work for AM/SSB transmitters such as CB. Most tube type amps are class A or AB. Transistorized amps are 50/50...some are Class AB, some are C.
Ok, there's my class for the evening!
Hope this helps,
Mr_RF |
don
| | Posted on Friday, January 18, 2002 - 1:52 pm: |
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Mr.RF, thanks very much for the info. Do you know what class the kl amps are? |
Mr_Rf
| | Posted on Sunday, January 20, 2002 - 5:38 pm: |
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No, sorry...no knowledge of the various CB amps. Never owned any! |
Mrsandman
| | Posted on Sunday, January 20, 2002 - 6:32 pm: |
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why does my 3 pill class c key on a ab tx667 5 pill |
bruce
| | Posted on Monday, January 21, 2002 - 11:56 am: |
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i dont get that? |
Mrsandman
| | Posted on Monday, January 21, 2002 - 6:24 pm: |
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bruce read mr rf story agian please on what he said about class amps maybe i missed something |
Warlock
| | Posted on Monday, January 21, 2002 - 10:15 pm: |
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In the CB world....
class C = highest efficiency
class B = highest efficiency with clarity for ssb
class AB = less efficiency with clarity (ssb)
This does not mean that every amp builder takes time to do it right.
Some class C amps are very clean and work extremely well on AM.
Some class AB amps are dirty as sin and perform poorly on AM, much less SSB.
The KLs are supposed to be class AB. |
bruce
| | Posted on Tuesday, January 22, 2002 - 12:08 pm: |
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warlock if you use a REAL class c amp on AM there is no way it isnt going to sound like poop. most problems with the ham radio amps ive used on 2 meters so the same should apply to cb come from a lack of understanding that a 100% modulated 4 watt am signal is realy 8 watts and if you squze it into a 4 watt max amp you get compression and a rise in distortion... remember you cant get 5 lbs of poop into a 4 lbs bag without conpressing it! I run a heath kit amp on 2 meters on ssb which allows a 1-10 watt input for 40-100 watts outby holding the drive to 5 watts (70) out it works just fine. The simplest way to set drive is crank it up till the output stops going up then drop the drive to 1/2 that level. You will find that the output of most amps will sound quite clean this way. |
Vernonott
| | Posted on Tuesday, January 22, 2002 - 3:50 pm: |
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Bruce : My class c driver doesn't do well by itself but does a beautiful job while driving my Nitro 700. |
bruce
| | Posted on Tuesday, January 22, 2002 - 8:22 pm: |
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then its not being driven class c |
Warlock
| | Posted on Tuesday, January 22, 2002 - 8:40 pm: |
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As to the class C:
I am by no means an electronic engineer. My knowlege in amplifier classes is basic but usable. Class C means the "on" cycle is less than 180* is it not? Meaning carrier must be present to activate or switch "on"? Class B over 180* (slightly) so as to have the transistor "on" to alleviate switching distortion, then AB and A continuingly higher in the cycle and lower in efficiency. Am I missing something? If so fill me in. Keep it simple as I'm not that bright.
As to the drive, these things can vary considerably. My rule of thumb is to drive the amp so that it's AM carrier (final out with amp full on) is 25% of the amp's peak talk power. This typically keeps things clean on the scope and analyzer. On ssb I set the exciter (radio) to drive the amp to 90% of it's peak talk power.
These methods have always worked well for me. Maybe ignorant, maybe simplistic, but it has worked. |
bruce
| | Posted on Tuesday, January 22, 2002 - 11:59 pm: |
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warlock what you said is 100% ... well 99% true there are disputes about amps the class C amp is on only 30 % of the input cycle so distortion is very high if your running cw or fm you do not care am-ssb get trashed |
Warlock
| | Posted on Wednesday, January 23, 2002 - 5:53 am: |
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I have put (I had a guy that knows what the hell he's doing) a class C amp on a HP analyzer. The particular one we tested was very clean if not overdriven, cleaner than the equivalent class AB Texas Star.
The amp(s) I currently run are class B. Boy do they get alot of compliments both AM and SSB. |
bruce
| | Posted on Wednesday, January 23, 2002 - 12:05 pm: |
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Warlock if you drive a class c amp that is self bias lightly you are most likley driving it at class b. No class c amp is going to look clean on am or ssb. I have done that on 2 meters it will work but only over a small range. Remember the input curve of most transistors in not a vertical line you dont go from no to full current in a .001% input change although switching transistors try too. Look up the drive requirements for the transistor you are useing and i think you will find to get to class c you got to hit it hard. |
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