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All things being equal: AB vs C

R

ROC1

Active Member
Apr 5, 2008
112
9
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I've read through a bunch of the posts on the site that remotely compare the AB vs C bias amps... Typically when someone mentions that ab is "cleaner" someone replies, "yes but not neccesarily... garbage in garbage out".

So lets take this scenario...
- Stock Uniden/Cobra CB (11 meter only rigs, no 10 meter, no ssb);
- Running in a stock volt application (amps are not volted - we're not in a key down competition)
- keeping final outputs within the manufacturers recommendations (not trying to squeeze 150w out of a 100w transistor).

Amps:
Texas Star 1600 V (2x8) AB-1
Dave Made 2x8 C

What would we expect to hear in terms of audio clarity/distortion?
Would there be any audible difference between the two?
How would these signals look on a scope/sa

If the goal isn't to wring every last watt out of a box, and audio/signal quality is a priority (or as much as it can be in the CB world), is there an argument for AB-1 or is a CB amp a CB amp and in this setup, little to no difference on the receiving end?

I ask because it seems to me when I here guys I know talking on C class; the audio sounds "sharper" on the edge of distortion. I know in a couple of cases they are running radio's nearly identicle to mine, but there are also a lot of other factors I'm sure. I'm the only fool in the area running AB-1 so I have no idea what my signal sounds like. I'm at a cross roads here as a bad jumper sent my sweet 16 up in smoke... one of the times I actually tried to feed it full drive and poof. Now I need to decide if I want to go back to AB or make the jump to C... for me sound on the receive as well as a clean signal on the spectrum analyzer & scope (again clean being relative here to 11 meter) are priorities...

Input?

Thanks... (y)
 

My comments in no particular order:

"Clean being relative here to 11 meter" -- "clean" is clean; there's no "relative" involved. To determine the "cleanliness" of a signal, don't rely on an oscilloscope; the only thing that will provide a meaningful answer is a calibrated spectrum analyzer (SA).

"when I here guys I know talking on C class; the audio sounds "sharper" on the edge of distortion." That's because it is. I'd venture a guess and say that when you hear such a station, you'll hear it on more than one channel (SA would show this).

A clean radio (meaning one with an AB final and not overmodulated), driving a well-designed and well-built amplifier within AB parameters, will win the good audio contest every time. And as a plus, a lot more of the signal is on the right frequency and not spread out from heck to breakfast.
 
the Col. who owns http://ampsrus.net/main.sc has a line of amps called annaconda . he says a spectrum anylzer is used on them . ive herd fat boy does too . call the Col. and ask him , he can give you the info on his amps better than i can .

ive ordered things from him a few times and never had a problem .

found a thread about this from a lil while back .
http://www.worldwidedx.com/amplifiers/29159-spectrum-analyzer-amps.html

P.S. ampsrus is no longer assocated with renecks radio room that was originally the amprus forum .
 
990nj said:
Do any builders use spectrum analyzers in putting their amps together?
Click to expand...

Every amplifier that comes off the assembly line should be tested into a dummy load that's large enough to dissipate all the power generated, and the testing should include a full checkout with a calibrated Spectrum Analyzer over the full frequency range of the amplifier. Then the FCC Certification Label goes on the back, showing that the manufacturer stands behind his product. The testing procedure would be available to the public so a potential buyer could make an informed decision about which amplifier to buy.

That said, however: since CB amplifiers are illegal to begin with, the law doesn't seem to apply. There is no "industry standard" and probably very few of the guys who build these electronic abominations have ever SEEN a spectrum analyzer, much less know how to use one properly.
 
"probably very few of the guys who build these electronic abominations have ever SEEN a spectrum analyzer, much less know how to use one properly."

you're dead on Beetle.

both of the dealers mentioned routinely depict the 2879 as capable of delivering 250W. they can talk all they want about owning and using sa's but the advertising doesn't indicate that they have any bearing on their claims.

seriously, if the maximum collector dissipation of a 2879 is 250W (12.5VDC X 20A) then how does anyone with half a brain (builders and users) believe that they are capable of 250W output or 100% efficiency when referenced to the power supply input? these conditions are no more representative of an amplifier producing a LINEAR output signal than the amplifiers mentioned at the outset of this thread where 2X driver sections precede the main 8X pa sections.

why do you need 120 - 200W of drive for 8 devices that require no more than 30 - 40W of drive to produce a LINEAR output signal when properly biased? YOU DON'T!

the DM2X8 boasts 1700-2100W out at 13.8 from between 140-200A. that's anywhere from 212.5-262.5W PER DEVICE or 2100W from 2760W of power supply....where does it end? real power @ 27Mhz. is only 800-1200W. the other 900+W is the result of line-section oversampling of harmonics, intermodulation distortion products and rectifier non-linearity occurring in the measuring equipment, pure and simple.

as a result of their not realizing all of this, they're lying and you're buying.

"the Col. who owns ampsrus has a line of amps called annaconda . he says a spectrum anylzer is used on them . ive herd fat boy does too."

and both of them are lying to you and telling you that a 2879 will produce 250W+ of power but they don't, SO WHAT? what's clear is that they either don't understand what they're looking at or they simply don't care. all things here are anything but equal.
 
freecell said:
and both of them are lying to you and telling you that a 2879 will produce 250W+ of power but they don't, SO WHAT? what's clear is that they either don't understand what they're looking at or they simply don't care. all things here are anything but equal.
Click to expand...

that 250watts output comes from the harmonic power reading, which is falsely high due to the bird element being more sensitive to higher frequency energy outside their rated frequency range.
For example: a 25-60MHz bird element, reading the 54 and 81MHz harmonic as added power.
overdriven at 27MHz = 27MHz + 54 + 81 etc.. all summed and shown.
 
"the Col. who owns ampsrus has a line of amps called annaconda . he says a spectrum anylzer is used on them . ive herd fat boy does too."

and both of them are lying to you and telling you that a 2879 will produce 250W+ of power but they don't, SO WHAT? what's clear is that they either don't understand what they're looking at or they simply don't care. all things here are anything but equal.
__________________

the col. never said he was getting 250 per 2879 . befor all the crap with the forum happened i recall him stating in a few post that 125 or 150 (i forget which) was the most clean to expect from them .

there are certanly folks out there saying they can get 400 out of one though . i bet that sounds nice .
 
BOOTY MONSTER said:
"the Col. who owns ampsrus has a line of amps called annaconda . he says a spectrum anylzer is used on them . ive herd fat boy does too."

and both of them are lying to you and telling you that a 2879 will produce 250W+ of power but they don't, SO WHAT? what's clear is that they either don't understand what they're looking at or they simply don't care. all things here are anything but equal.
__________________

the col. never said he was getting 250 per 2879 . befor all the crap with the forum happened i recall him stating in a few post that 125 or 150 (i forget which) was the most clean to expect from them .

there are certanly folks out there saying they can get 400 out of one though . i bet that sounds nice .
Click to expand...


He doesn't have any descriptions on the anaconda amps but he's made some wild claims on the fatboys he sells.

AmpsRus.net - We specialize in sale & repair of cb radio and amplifiers. : 2X2879
 
Just a word about watt meters. They all behave/act the same way. A 'Bird' meter isn't any more susceptible to misreadings than others. Of course, some are sort of more susceptible than others, which is a product of circuitry design and quality control, and normal. Watt meters have no frequency discrimination ability, other than a very, very broad one. One designed for HF doesn't work too well at V/UHF and visa versa. They may read something in an out of range situation, but it isn't reliable, and only good for reference. It would certainly be nice, but then we aren't talking about a typical meter at all. Oh well, a Rolls' would be nice, but would sort of look funny in my driveway...
- 'Doc
 

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