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Sixkiller505
| | Posted on Tuesday, July 23, 2002 - 5:27 pm: | 
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i"d like to get a tech"s true input on this once and for all!! i have had some real knock down drag out verbals with good friends over this problem,and i"am sure other fourm members have too.if u have a 200 x-force(or magna-force they look the same)swinging 400watts(making you feel warm and fuzzy)and a texas star 500 doing 400 bird real watts(in theory) is"nt the texas star doing more?? and if so why buy the two pill that"s swinging volts and audio(we call pep watts) when you could have the 4pill doing real watts rms(theory) and how can the 2pill do 400 real watts anyway when 2879's are rated 100W is volt watts stronger than rms?or is volt watts basicly interference that makes your meter move,and when the smoke clears you are still just doing 200 WATTS!!!(2 PILL)those x-force look good ,but it"s a lot of money to spend for nothing,if volts just make you look good. thanks for your time. |
Tech671
| | Posted on Tuesday, July 23, 2002 - 11:13 pm: |
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If you search back in the archives this was gone over specifically. Let me try to summarize.
A 2sc2879 is rated at 100w avg power (rms) per transistor @ 12v with 4w avg (rms) drive. Avg power is not exactly rms, but very close and what the industry standard meter reads (Bird). Typically peak is 2.5 times over rms power. This can vary depending on the drive, voltage, input, modulation, etc. Most everyday charging systems float at 14.5v when the motor is running. A typical radio tuned, Cobra 29 let's say, does about 6w rms and 20w peak. Class C amplifiers will yield a higher efficiency than class AB, class B is somewhere inbetween but leaning to the efficiency of class C. Amplifier input and output tuning/matching, components, transformers, power supply, all can play factors in the output of every amp. These are general statements just to be as simple as possible and still give you some understanding.
A texas Star 500 using (4) 2sc2879 transistors in stock out of the box form usually does around 200w rms (Bird 43) and 500w peak (Bird 43p) with the radio mentioned above at typical auto voltage. This isn't spec sheet numbers, but on-the-bench testing.
A XForce 200hd using (2) 2sc2879 transistors in stock form with the same drive and voltage will do around 170w rms and 450w peak. The Magna Force 350 uses the same transistor compliment as the 200hd, but in class B mode, will yeild slightly higher output due to the higher gain (or lower sensitivity to drive) with equal drive of the radio.
Now if you compare apples a little closer to apples, the similar complimented XForce amplifier comparable to the Texas Star DX500 would be the XForce 400-12. This uses the same transistors and is class B biased. With the same voltage and drive scenario, the 400-12 does around 280w rms and 650-700 peak. So to answer your question, it is both "SHOW" and "GO".
You may think the outcome would change if you added a single transistor driver such as a Texas Star Mod-V. This is when the custom amp walks away. The Texas Star uses small 1" transformers designed to be as efficient as possible (and less expensive) with radio drive. A good running Delta Force will take this amp to it's "saturation" point. The XF uses a large diameter 2" transformer which can handle much more drive and heat.
Peak and rms work hand in hand in RF amplifiers that we typically use. The goal you should have as far as what an amplifier does in watts should be that the peak is 4x over the carrier, and that the rms wattage at least moves forward. Example, a Palomar/Boomer 225 you would want it to have a carrier around 50-60w in high power position. This will allow it to move forward in rms wattage when you modulate, and yield about 200w or so peak. If you have a 100w carrier and the wattage "backs up" when you modulate, you won't be as loud and clear, and likely muffled and distorted as well as the amp running much hotter.
In conclusion... does that make Texas Star a bad amplifier? No. Does that make Xforce the amp you need? Not necessarily. Every user has different desires. Each amplifier can meet certain criteria for the individual buyer, it just depends on what you're looking for. Sorry for the lengthy reply, but I feel the informed operator will spend his money more wisely and end up much happier with his purchase and end result. Remember this is simplified the best I can and general information for piece of mind.
Anyone wishing to discuss this further (with me) please do so by email so as not to tie up the forum. |
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