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Message |
    
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 426
Registered: 5-2004
| | Posted on Monday, May 16, 2005 - 9:08 am: | 
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Can anyone please tell me what the different classes of amp are and what it means for each class like what does class C mean ect.?
Thanks,
AP |
Bruce
Senior Member
Username: Bruce
Post Number: 2601
Registered: 9-2003
| | Posted on Monday, May 16, 2005 - 10:24 am: |
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GOOD QUESTION !
This is a simple look at them when i say ON it means the transistor is turn ON for that amount of time each cycle..... here goes .....
OK class A is on 100% of the time lowest distorton only 20-30% efficent
Class B is on about 50% of the time it will still work on AM/SSB and is 30-50% efficent
class C is off more that 50% high distortion but 50-70% efficent
Now class AB is somewhere between a and b. |
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 427
Registered: 5-2004
| | Posted on Monday, May 16, 2005 - 3:59 pm: |
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so class A is the cleanest sounding but least efficent and class B is in the middle and C is worst sounding but most efficent. Now you say B will still work on SSB, does this mean that A is good for SSB and C is not?
What would the best be for AM and SSB? what are class are the KLV series base amps and mobile?
I have a KL500 mobile amp and was wondering what class it is.
Lots of questions but I need to understand.
Thanks,
AP
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Tech291
Moderator
Username: Tech291
Post Number: 179
Registered: 11-2004
| | Posted on Monday, May 16, 2005 - 6:45 pm: |
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Roger,
Amplifiers can be Very Confusing!
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.
CLASS "D" operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each Sampling Theorem. Theoretically since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero (found by multiplying the voltage across the device [zero] times the current flowing through the device [big], so 0 x big = 0); and when the device is off, the voltage is large, but the current is zero so you get the same answer. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.
tech291
CEF#291
kc8zpj |
Tech808
Moderator
Username: Tech808
Post Number: 5765
Registered: 8-2002
| | Posted on Monday, May 16, 2005 - 8:54 pm: |
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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 are single-ended designs with only one type polarityoutput devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, 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.
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 due 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 allows both devices 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 demands. 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 D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.
Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.
Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.
Lon
Tech808
CEF808
N9OSN |
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 428
Registered: 5-2004
| | Posted on Tuesday, May 17, 2005 - 7:33 am: |
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thanks for all the great info it helps very much,now does anyone know what class the KLV base and KL mobile amp are? my instructions dont say or the copper online catalog dont say.
I have a chance to buy a Big a** base amp and its a 1-2879 pill driving 4-2879s with var. out put class C and it`s supposed to give around 500-1000 pep. I was thinking of getting KLV1000 but like the idea of not having to adjust for channel changing. I dont know which I want. Maybe some one can help me make up my mind.
Thanks,
AP
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Thehobo
New member
Username: Thehobo
Post Number: 5
Registered: 2-2004
| | Posted on Tuesday, May 17, 2005 - 1:17 pm: |
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say hey ap, maybe i can, in laymens terms help you in your situation!! ahem, lol.. ok, most klv amps are of the ab, or ab1 class!! they are a good reasonable all around amp!! ive had them all, and enjoyed there preformance!! still have a 4 tube klv!! now as far as retuning when you change channels, ive found thru my use of them, that if you tune for ch, 20, you can go up and down abot 12 to 15 chs. with out retuning the amp!! how ever, the amp will have a tendecy to fall off somewhat after 10 chs up and down!! a tube amp will handle a swr differance somewhat better then a pill amp?? especially when you start to get somewhat up in the wattage!! most BIG pill amps dont like anything higher then a 1.3 to 1, swr!! wereas a tube can handle almost a 1.8, and at times a 2 to 1 swr?? mite not like it, but the tubes are more forgiving!! if your planning on getting a 1x4 pill amp and its a mobil, youll need rite at a 150 amp power supply to really handle the power?? if its a plug in the wall, ok no need for the power supply!! ive got and use both types of amps and i personly cant tell you which i like better??? i do really like the klv tuber on ssb, as ive always got good reports on it!! the pill amps, you really have to watch the drive and dead key somewhat closer!! ok, rattled on enough, hope this mite help you or others some.. enjoy.
thehobo
274150 am
monitor ch. |
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 429
Registered: 5-2004
| | Posted on Tuesday, May 17, 2005 - 7:31 pm: |
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Thehobo,You helped me Thanks alot,I always come back to the KLV 1000 or KLV 400. I was looking at alot of amps and just want the best I can get at the most resonable price. It`s just the more I looked the more I was unsure of what they are all about. alot of manufactures of amps dont even say what class. I did`nt want to spend alot of cash just to be unsatisfied.
All the help here was great and I know what I want.
AP |
Bigbob
Senior Member
Username: Bigbob
Post Number: 1914
Registered: 12-2001
| | Posted on Tuesday, May 17, 2005 - 8:17 pm: |
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Get a klv 550 600 watts on high no tuning and drive it with no more than 4 watts 2 is better.Drive is more important than swr,have driven my boomer 400 with 6 watts into a 2 to 1 swr for 2 hours before I noticed,just slightly warm,now you if you hit a texas star 667 with 6 watts for 2 hours no matter what the swr them final pills are toast.Keep the drive down to 2.5 on 2-stage amps and all is well,on high drive amps 4,6 sometimes even ten watts won't hurt them,that depends on the pill input rating.Bigbob |
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 430
Registered: 5-2004
| | Posted on Wednesday, May 18, 2005 - 11:06 am: |
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One more question, Iwas told by CBers in my area that If I get the KLV1000 I should leave it on all the time so the tubes last longer.
Is this fact or fiction?
Thanks,
AP
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Chad
Intermediate Member
Username: Chad
Post Number: 287
Registered: 11-2004
| | Posted on Wednesday, May 18, 2005 - 11:54 am: |
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Fiction,
Now I would not be turning the filaments off if you plan on coming back in 30 minutes, but it in no way will increase tube life leaving it on 24-7.
Think lightbulb.
I rarely see bad filaments in tubes, usually it's just time to replace or the tube has been abused.
DO let it warm up well before applying plate voltage to prevent cathode stripping of the tubes.
http://www.chiark.greenend.org.uk/scopes/weyer.txt
Granted it has to do with audio tubes, but a bottle is a bottle 
Chad |
Bruce
Senior Member
Username: Bruce
Post Number: 2622
Registered: 9-2003
| | Posted on Wednesday, May 18, 2005 - 12:33 pm: |
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Some tubes are left on at a reduced voltage however i doubt if this will make any major diffrence on most tubes. |
Thehobo
New member
Username: Thehobo
Post Number: 6
Registered: 2-2004
| | Posted on Wednesday, May 18, 2005 - 1:27 pm: |
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ap, when i use my klv tube types, if i think im going to use them that day, ill turn it on to stand by at least 1/2 hour before use, then if i think ill be using it for the rest of the day, i leave it on!! but when done for what ever, i turn it off!! if used next day, same proceedeur!! there is the 550 klv that is mention above, its a nice amp for the money, but there agin, its for a single final radio!! put about 11/2 watt drive in and let swing!! the box has 6 power levels and there nice to have, but on mine ive found that 2nd and 5th position to be the most usefull!! but each owner will have his favorites!! one advanage of the 550 is turn it on and go, no adjusting and no tuning, just make sure your dk from radio is around 2 watts?? agin, i hope all of this and the above info helps you or whoever in there choises..
thehobo
274150 am
monitor ch. |
Airplane1
Intermediate Member
Username: Airplane1
Post Number: 431
Registered: 5-2004
| | Posted on Thursday, May 19, 2005 - 8:22 am: |
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Helps very much, thanks alot guys.
AP |
Patzerozero
Advanced Member
Username: Patzerozero
Post Number: 778
Registered: 7-2004
| | Posted on Saturday, May 21, 2005 - 7:17 pm: |
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if you're changing freqs a lot airplane, transistors are easier then retuning tube units all the time. of course the tube units MAY tolerate swrs over 1.5:1 better then transistor units.
the 1 x 4-2879 base amp, depending on who built it, is probably supplied with closer to 18 volts then 12, by its built in power supply. hence the 1000 watt or so swing. dead key is still in the 250 watt range for reliability.
as for it being class C, 99% of those you talk to will NOT be able to tell the difference if you drive it low on SSB. just make sure it has SSB delay built in to it if it's a class C. no delay won't hurt anything, except the relay eventually, but it is annoying to listen to the constant chatter. on dx on SSB-even less will know it's an 'AM' amp.
in general, to get the same output, from the same transistors, class C requires more input then B or AB. |
Couchpotatoe
New member
Username: Couchpotatoe
Post Number: 4
Registered: 6-2005
| | Posted on Monday, June 13, 2005 - 9:02 pm: |
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I'VE BUILT A 1 X 4 MY SELF.
1 SD1446 DRIVING 4 2SC2879.
1446 HAD .5" BASE AND 1" COLLECTOR TRANSFORMERS BOTH WRAPPED 4T. 2879'S HAD .5" BASE AND 1.5" COLLECTOR TRANSFORMERS BOTH WRAPPED 4T. EACH TRANSISTOR STABILIZED WITH 100PF COLLECTOR TO GROUND. IT WOULD DO A DEAD KEY OF 150 AND 800 WATTS PEP SWING ON 15v AND TO USE A 2SC2879 FOR THE DRIVER WOULDN'T HAVE GAINED ANY OVER THE SD1446 AS FOR NOT BEING TO TELL THE DIFFERENCE FROM A, AB, C...FROM MY EXPERIENCE CLASS C AMPLIFIERS HAVE A TERRIBLE CRACKILING POPPING SOUND FOR THE ONE TALKING ON ONE. I HAVE A NEIGHBOR 2 MILES AWAY FROM ME AND I HAVE CHEWED HIM OUT MANY TIMES TO PUT A .7VOLT BIAS TO HIS OBNOXCIOUS SOUNDING HOME-MADE AMPLIFIER. I DO BUILD THESE THINGS ONCE IN A WHILE. |
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