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Tech181
| | Posted on Tuesday, December 11, 2001 - 9:25 pm: | 
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I have heard and seen a lot of claims regarding output power as it pertains to amplifiers. Some people make some of the most outlandish claims regarding the amount of power a transistor (also called "pills" because of their resemblance to aspirin) are capable of.
In my experience, I have found that no matter how hard you drive an amplifer, it DOES have a ceiling as to how much power you can get out of it. Allowing your input to maintain an output constantly near that ceiling will result in a shortened life of the internal components, especially the pills.
Some people claim you can get 900+ watts out of a Texas Star 667. This is just not true. I don't care what you do to that amplifier, you will not get that kind of power out of it. Heavier wire, extra batteries, bigger alternator, etc. will NOT give you ANY more power out of this particular piece of equipment that the transistors can produce. Of course bigger power wire, and a larger alternator will help you achieve the maximum output and effiency from the amp, you will not get more out of it than it can possibly produce. Period.
How much power can you get out of an amp? That depends, of course the amplifier you are running, and the way it is installed and set up. Be sure to use heavy gauge wire for long runs and be sure your alternator can handle the load. Putting a 667 in a Ford Festiva is asking for trouble. Be sure your alternator will be able to handle the load of your amplifier while still being able to use your headlights, heater, and other high amp accessories.
While proper installation using quality components is key, the rest is up to the amp itself.
Let's take a look at the Texas Star 667V. This rig is powered by one (1) 2SC2290 transistor driving four (4) 2SC2879 transistors. The main reason for the driver is to allow the user to get full power out of all four of the 2879 pills. Most radios lack the power to signifcantly power all those transistors to their fullest capability.
The 2SC2290 transistor is manufacturer rated at 70 watts. The 2SC2879 transistors are manufacturer rated at 100 watts a piece. Knowing this we can easily see this amplifer has one 70 watt transistor driving the four 100 watt transistors.
In my experience, I have seen that most transistors are rated kind of on the low side by the manufacturer that produces. This conservative estimate may be attributed to several things, but most transistors are rated on the low side nontheless.
From what I have seen and experienced, a transistor will put out 125% of it's manufacturer rated output. But this is it. Absolutely no more. Knowing this we can easily estimate the output of the 667 as 500 watts PEP. That's four 100 watt transistors performing at 125% which is an additional 25 watts a piece. Multiply 100 watts times four, and you get 400 watts. Add this total to the extra 25 watts out of each of those four transistors which is 100, and you get your grand total of 500 watts.
What does the "667" mean printed on the cabinet of the amp? Who knows? As with all the other amplifier manufacturers, the number on the outside is pretty meaningless. As far as I can see, it's a sales pitch. The bigger the number the "badder" the amp sounds, which in turn may generate more sales.
Some people throw meaningless acronyms into the equation like PEP and SSB. Well, PEP is Peak Envelope Power, the absolute top power possible, and since sideband emissions generally produce higher output power than AM emissions the false sense of a higher power through sideband use is produced. Hence people think they are getting a piece of equipment capable of putting out more.
The fact is, the amp is only going to put out as much power as it is built to put out. Driving the amp with more power (watts in) will only result in heat and potential damage to the amp. But it will NOT result in more power. You are only going to get out of it what it's built to do, not what someone says it will do.
"But I get more out of my amp than you say is possible! You say I can only get 500 watts out of my amp and I am getting over 550 out of it."
This is where I think alot of people get their inflated power outputs. It's called reflected power. You see, high SWR will be shown as higher output power, giving the false impression of more power out on the meter. The best way to measure your output is with a meter that shows reflected power by the way of a dual-needle meter or one that shows the relative percent of power reflected back at different levels of standing wave.
I am working on doing a review of the KL300P amplifier and my theory holds correct.
The KL300P contains two (2) SD1446 transistors, factory rated at 70 watts a piece. The most I could hope for was 87.5 watts each for a total absolute output of 175 watts. I was getting 180 out of it. However I had an SWR of 1.4:1. At this SWR I had a reflected power of approximately 3 percent. 3 percent of 180 is a little over 5 watts. Hence the actual forward power was around 174.6 watts. Pretty close in my book. I drove this amplifier as hard on both AM and SSB as I could and still could only get 175 watts out of it.
As you shop for an amplifer try and remember this. Don't judge the amp by what's printed on the cabinet or what the dealer says it will do. Find out how big the transistors are in the amp and how many of them there are. Then you will be able to make an educated assumption as to the REAL power output. Below I have listed some commonly used transistors and the power output rating put on them by their manufactures.
Happy DXing!
2SC2290 -- 70 Watts -- 87.5 MAX
2SC2879 -- 100 Watts -- 125 MAX
SD1446 -- 70 Watts -- 87.5 MAX
MRF455 -- 60 Watts -- 75 MAX |
Bigjohn16
| | Posted on Tuesday, December 11, 2001 - 9:41 pm: |
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Tech 181,
Since your talking about the TS 667, and have answered questions about my setup in another post, can I please ask you another?
Since I run the TS 667, behind a Galaxy 99, Ive heard many people talk about the dead key feeding it. The Texas Star spec sheet says to get 500 watts, dead key at 4 watts. But others say no more than 1 1/2 to 2 watts. I have set my Galaxy 99 to dead key at 2 watts on the low side. Where should I be??
Thanks,
John |
Jyd
| | Posted on Tuesday, December 11, 2001 - 9:56 pm: |
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he is right the factory anly rates them at 75% of what the transister will do so 2879-100 at 75% and if they operate at 125% 125watts. i wish i new what him and 307 does i would not have to ask 10 questions a week, ha anyway they both know their stuff for sure |
Bigjohn16
| | Posted on Wednesday, December 12, 2001 - 12:46 am: |
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Tech 181,
Thanks, I'll leave it at 2 watts...
See ya,
John |
Warlock
| | Posted on Tuesday, December 11, 2001 - 11:26 pm: |
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To carry this a bit further.....
2879's are rated at 100w pep power with 10w pep drive @ 12.5v.
(4) 2879's =400w, right? requires 40w pep to obtain that at 12.5v. Now increase the voltage to 14.5 (typical of today's charging systems), that's about a 17% increase, taking power output to about 470w. Increase the drive by 80% (from 40w to 70w) and power is now 840w. Now add your 25% over mfrclaim and you're at 1050w. Now subtract amp efficiency (class AB about 60%) you now are back to around 630w. The 2290 is rated at 70w pep with 4w pep drive @ 12.5v. Obviously most radios are 4 times as much drive, so a litlle more top end will be produced due to higher drive.
That's where they get 667 from.
Class B or class C amps will produce even more due to higher efficiency.
So bottom line, seeing as much as 900w from a 667 is possible, but it would be at a voltage feed of close to 16v with upgraded feed wire and bypassed fuses.
Now, remember that recommended drive for the 2290? 4w pep? A little scary thinking you're dumping 4w carrier into that little kl40 or 60?
It's a good idea fellas to have those radios matched to your amps. You don't want the amp to have more than a 30% carrier as to it's peak. |
Taz
| | Posted on Wednesday, December 12, 2001 - 8:57 am: |
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how abot the mrf-422's |
Jyd
| | Posted on Wednesday, December 12, 2001 - 4:08 pm: |
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really i messed up 75% at 100watts and 150watts at 125% |
Jyd
| | Posted on Monday, December 17, 2001 - 7:56 pm: |
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181 is right,the other dude needs to look at factory specs at 3watt deadkey a 2879 is at 75% at 100watts and 125% would make it 150watts.181 said that they will run at about 125%.ad it up |
Jyd
| | Posted on Monday, December 17, 2001 - 8:00 pm: |
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667,650watts-600 on bird meter we checked it with a galaxy 99 pushing the 667 |
Warlock
| | Posted on Monday, December 17, 2001 - 10:15 pm: |
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Again, most late model autos and trucks charge at 14.2-14.8v, real world. |
Eagle
| | Posted on Monday, December 17, 2001 - 11:52 pm: |
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where could i find a good selection of amplifiers?
what brands do you recommend? does copper sell any?
thanks |
Jyd
| | Posted on Tuesday, December 18, 2001 - 10:48 am: |
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i think this is funny,bicker over amp power, so at 14.8volts the 667 0nly done 600 on a bird meter being push by a 99 so that is relitive power output for a 667. it also depends on what meter you have. i would like to get the one 181 is talking about were 2 needles swingover each other,what is it called 181? |
Eagle
| | Posted on Sunday, December 23, 2001 - 10:12 pm: |
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Is there ant way to judge what the output of tube base amps should be? And how can you tell who made the amp if it is not written on it? |
Scrapiron63
| | Posted on Sunday, December 30, 2001 - 3:43 pm: |
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Hey Eagle, those early amp builders didn't put a name on sometimes, since they were illegal, kinda like breaking in a bank and leaving your business card. Can you describe the amp, the number of tubes, and the kind of tubes. scrap |
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