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Clean Signals from C Class!!!

I really only seen most class c amps used for long rtty sessions. Tubes can loaf at full output vs linear operation.

I don't know much about amps. I have never owned anything other than a few small solid state amps over the years. Most of what I've learned is from hanging out in friends shacks who are QRO junkies.

And reading here(y)
 
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I am wanting to clearly state that I offered up the recording of my QSO (I think it was the second recording in the thread) as one to critique in the interest of understanding what is good or bad with amps. I have not attempted to make any argument in favor of using class C amps for any mode of transmission. I realized that when once I produced the recording as one in which I had used the class C amps (not in use now) I could be opening myself up to scrutiny. I was and am so willing despite it being neither my intention nor the intention of this thread. I have no agenda except to participate in the process of education and learning. I am not advocating anything. So let me be perfectly clear, I, Homer, am neither a liar, nor a sheeple with regard to this subject, nor any other on the forum.
I maintain my confidence in the right of all people to make their own choices. I am here to have fun and learn.
Thanks for the opportunity.
 
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I just wanted to throw a wrench into this topic...

On any plate modulated AM transmitter, the final stage is always and must be ran in class C. Does anyone know the reason for this? (I know, but just wanted to test the knowledge of the crowd here.)

Kudos to User "JustinDePolis" in post #66 of this thread. ;)
 
The best thing to do is to NOT run a box to begin with.... Put your time and money were it REALLY counts up at the ANTENNA!!!!!
 
If you run a clean un-modded/clean radio thru an AB amplifier to a C class splatter box, will the signal still sound splattered coming out of the C class amp?

Just some thoughts I had!! 1-5.
If you carefully placed a filet mignon, a side of lobster and a flat of caviar into a blender set on high...

The best thing to do is to NOT run a box to begin with.... Put your time and money were it REALLY counts up at the ANTENNA!!!!!

I really don't see this as necessarily a mutually exclusive issue; either a wonderfluous antenna system or an amplifier - why not do both, thus insuring the best possible chance of contact?
 
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I'll tip my Texas 10 gallon hat to Homer for posting up on this topic. I've talked to Homer both locally (while working/travellng NW Arkansas) and via DX, and he always sounds good on my end. Whether I'm 5 miles away or 500, there is no crispity crunchity class C sound. I can't explain why his setup works, but it does. Can't say what his transmission looks like on a scope or if he has harmonics on 3 other frequencies, but it does SOUND good.

Personally, if I had it all to do over again, I'd have saved my money on my Texas Star DX500 and Iota power supplies and just bought a big honkin' amateur tube amplifier. But that's another thread. :laugh:

73,
RT307
 
I'll tip my Texas 10 gallon hat to Homer for posting up on this topic. I've talked to Homer both locally (while working/travellng NW Arkansas) and via DX, and he always sounds good on my end. Whether I'm 5 miles away or 500, there is no crispity crunchity class C sound. I can't explain why his setup works, but it does. Can't say what his transmission looks like on a scope or if he has harmonics on 3 other frequencies, but it does SOUND good.

Personally, if I had it all to do over again, I'd have saved my money on my Texas Star DX500 and Iota power supplies and just bought a big honkin' amateur tube amplifier. But that's another thread. :laugh:

73,
RT307
AM or SSB? AM likes class C and it's definitely more efficient, typically about 75% where AB is only typically about 50-55%.

On SSB, IF you keep your audio high enough you will force the class C amplification transistors to stay open, especially if you have some sort of background noise, but that's the problem with class C, the notch between on & off is so wide that it loses the more soft & subtle nuances in the audio transmission, causing that dirty gritty tearing sound.

One mistake a lot of ops make when running a class C amp is to lower the mic gain thinking it will help stop what some people may tell them sounds like over-modulation, -when turning it up is actually what's needed to sound 'better'.

Remove the subtleties by increasing the audio/mic gain and the amplification stage stays on more and sounds 'better' - more or less.
 
FWIW just because a signal sounds clean to the ear it does not mean it is a clean signal. People have a difference of opinion of what clean is. Mine is a signal free of distortion and harmonics as well as in band spurious signals causeed by poor IMD and not splattering upanddownthe band.
 
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In my experience, the Class C boxes work only marginally well on AM. That depends on a couple of factors. For one, that the operator knows how much input to give the amp and not over-drive it. The other is that he is keeping his modulation just below 100%. Those two things make a big difference. Not that it would be truly clean; but at least somewhere clear and understandable.

Unfortunately, many AM operators don't know how to do that. They just plug whatever radio they happen to have into whatever amp they happen to have - and think that everything is just fine. Here is a news flash - it isn't OK. Sounds like trash. Don't kid yourself either - it really is trash. Not knocking it; just calling it as it really is. If you have ever turned up a radio or TV too far, what you get is audio distortion - and so will over-driven transistors distort an amp. More importantly, it can damage the amp. More amps get burned up by not running the right amount of input power from the radio to the amp - than any other reason. Just a fact.

However, the BEST operators use an AB class amp and know how to drive it. They read the amp's specs and follow it for best results. They are clear and easily understood and aren't trying to get every watt out that they can. It is the difference between doing it right, or just hooking things together and just hoping for the best. So what if the amp is a TX-400 and you get only 320 watts of clean power out of it? It will last longer, not overheat, not destroy the expensive transistors, and just sound and work better. Just another fact.

So - to answer the original post - I would say just run the AB class amp. Don't get all wrapped up and fall into the trap of obsessing with getting all of the power you can. Make sure you don't over-drive the amp - either. VERY important! So what if you don't run as many watts as another local does? Within a close distance/locally, the extra power adds/does nothing at all. The AB class will work outstanding on AM and SSB; but the class C amp will barely work OK on AM (if set up properly) and just work plain crappy on SSB.

When doing DX, then the same situation exists. If I had a choice to run a 150 watt AB class and a 300 watt C class, I would pick the AB class every time. 150 watts of AB power and making sure that the radio output is matched to the amp input requirements when DX conditions are in - is a winning combination every time. Even if your antenna isn't the best there is.

Base:
P/T COBRA 146GTL(Spare)
President Jackson
Turner +3 Hand Mic
Pyramid 25 Amp P.S.
Home Made Ground Plane Base ant.

If this is your base setup; then consider turning down the dead key watts of that 146GTL or Pres Jackson down to 1 watt swinging to 4 watts on AM. Then, turn down the ALC until you get 9-10 watts for SSB with 'ahhhh' modulating.

That 150 watt AB amp may have two MRF-455's or 2sd1446's transistors (they are basically both the same transistor under different mfrs/numbers). Those kind of transistors are very commonly found in many AB class amps. They are a very low drive transistor that are EASY blown if too much power is applied to them. On the other hand, they are excellent transistors for both AM and SSB so long as you input watt them correctly. In truth, one of these 150 watt/1446 2 pill amps will put out only 130 watts clean at ~14 volts.

Now here's a thought. You might consider selling the C class amp and getting an antenna with better gain. An antenna with real gain is like running an amp. If another antenna has more gain than the antenna you use now - this will make a HUGE difference when transmitting. A 1/4 wave antenna has 'unity gain' (no gain; no loss). But a 5/8 wave antenna will have as much as 5db gain over the 1/4 wave antenna - which is the equivalent of running a radio that has 4 times the power output of the radio you now use. That change ALONE makes a BIG difference. An amp can give you gain; but so can a better antenna.

It is easier to understand someone who is running clean rather than someone just stuffing an inefficient antenna full of garbled watts. Hooking up two amps together - just to attain more watts - shouldn't be the goal - IMO. The kind of plan you are proposing usually leads to the destruction of both amps - eventually. Not saying it cannot be done; but very difficult for a beginner to get the details right.

That decision is up to you.
Hope this helped you . . .
 
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AM or SSB? . . .
I am almost exclusively a SSB operator.
I run my modulation under 100%.
I use an RCI 2950.
I work DX almost exclusively on the low power setting on my little amp when it is on, which is good for about 125 W PEP. All I presently have is the Palomar 250 Lizard (The tube I need to repair my base amp requires I refinance the mortgage to afford, so it is an unfortunate circumstance I have to deal with). I drive it with a one watt dead key when on AM, and, as we know there is no DK on SSB.
I use a handheld Astatic 636L noise cancelling mic.
I use a variety of antennas, and some are not as efficient as others, no doubt, but I have just put my 4 element Yagi back up. If an antenna bores me, or doesn't work well, I replace it with another. I depend on my antenna for most of the work my station does.
I hope the listening experience is as good for everyone as it has been for Brett, 2RT307. We have talked to each other while I had up the Yagi, EFHW, dipole, AP, and Sigma4 homebrews. We get lucky sometimes.

Homer
 
This subject keeps getting repeated over and over because those who don't know, will not or cannot understand the reasons for amplifier operation in class A, B and C.
Those who know are not listened to by those who do not know so the foolishness keeps rolling on and on.
FOR SSB;
.
Class C operation has the bias set to A POINT BELOW the 'CUT OFF' of Plate/Collector current.
When drive is applied the device is driven up out of cutoff by varying voice rates.
THIS IS WHERE MOST OF THE DISTORTION and SPLTTER PRODUCTS COMES FROM.
Part of the drive never get through the amplifier, especially the low amplitude part of the driving signal. The parts the do break the device in to conduction is so abrupt that the distortion and splatter is produced.
.
.CLASS B operation is a little better but can still produce some of the same undesirable products in a single 'ended amplifier' this means (not push-pull).
.
Class A operation has the plate/collector current flowing at about 20%+/- of total current. This makes the amplifier about as Linear in operation as the devices will give and generate the least undesireable products.
.
. WHAT does Linear mean? A near faithfull reproduction of the driving signal.
Class C cannot do that being biased below device cutoff and losing part of the drive signal plus causing products that are not normally in the original driving signal.
.
Some other supporting comments are you would never run an audio amplifier class C and put up with the distortion on your favorate music so why do it with an RF amplifier that would not be running in true Linear mode?
The other side of this is most of you do not know when enough drive is enough. How would you know unless you understood the principles behind bias levels vs the specific devices in the amplifier?
Take a look at all the amplifiers that have been roasted because the user did not know better..
Lastly, it's aways a joke when you tell an op he is splattering and a mile wide and he comes back with "it must be your receiver" when 'he' is generating the trash 'he' cannot hear. Under what basis would he know your receiver has a problem; he dosn't!
Hope this helps to settle some of the on going unwillingness to accept the technical facts.
Even if you don't understand them, just believe it.
Good luck.
 
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That 150 watt AB amp may have two MRF-455's or 2sd1446's transistors (they are basically both the same transistor under different mfrs/numbers).


Just noticed this Robb.Two things I see wrong. First, do not confuse a 2SD1446 with an SD1446. They are completely different devices. The 2SD1446 is a Darlington pair in a TO-220 case with very high gain for power amplification........but not RF power amplification.......usually meant for switching. The SD1446 is a VHF RF power transistor in a 211-07 case like the MRF-455, but rated at 70 watts out but requires 7 watts of drive to achieve that. The Motorola MRF-455 is rated at 60 watts out but with only 3 watts of drive and is only rated to 30 MHz. making it an HF device. The MRF-455 and the SD1446 can hardly be thought of as " basically both the same transistor under different mfrs/numbers" just because they are both used in RF amps.

2SD1446 datasheet and application note, data sheet, circuit, pdf, cross reference | Datasheet Archive


http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2805.pdf


http://www.macomtech.com/datasheets/mrf455.pdf
 

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