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How many watts from a 2879

Discussion in 'CB and Export Equipment and Accessories' started by 543_Dallas, Mar 20, 2018.

  1. 543_Dallas

    543_Dallas Sr. Member

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    It was mentioned in another thread that W8JI, the well respected engineer that designed many of the Ameritron amplifiers and medical devices, made some comments about CB leenyars on the qrz forum. I thought it was a good read.

    https://forums.qrz.com/index.php?threads/2sc2879-producing-250-watts-hahaha.248732/

    Quote w8ji

    "Just out of curiousity I bolted up a single 2SC2879 in class C (zero bias) in a single ended amplifier with resonant transformer. Heatsink is massive and I used a soft copper gasket for better heat transfer, no grease.

    On 5 MHz I can easily push it to 30 amps Ic at 18 volts and get almost 300 watts output. At about 30 amps my supply shuts down. I didn't filter the output beyond the resonant transformer but the 2nd harmonic was about 15 dB down and 3rd harmonic much less level than that. Harmonics were pretty much gone after the third. The harmonics clearly contribute less than 10% to the output measured.

    The statement a single 2SC2879 can produce 250 watts is accurate, so long as linearity and long term reliability are not factors, and the 250 watts does not have to be "harmonics" or things that mislead power meters (although this could be true in some cases)."


     

  2. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    See if you can calculated the Junction temperature. There is a figure that you must never exceed and is the reason they have derating curves and device dissipation.
    Once that figure is exceeded the transistor fails very very quickly.
     
  3. StrangeBrew

    StrangeBrew Sr. Member

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    For a comp box it only has to last for that one keydown.
     
  4. bob85

    bob85 Supporting Member

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    once upon a time in a basement in NJ there was a cber who was smarter than the average bear,
    he understood which parts of the datasheet were important to win keydowns ( radio drag racing ) & which were not,

    He knew that doubling your vcc would give you 4x the output power if it would hold together,
    he also knew that increasing voltage can get you more power without destroying the imd of the amplifier,

    he realised that if he could increase vcc a reasonable amount without exceeding breakdown voltage & raise load impedance so as not to exceed a 2879's current limit, get the match pretty good when driven flat balls out & not overheat the ferrite,

    he could easily make more much power than the guys using conventionally designed amplifiers,

    he dreamed of a 2pill destroying old school book built 4pills, cutting their lips off,
    he tried numerous matching techniques, different combining methods for the larger amplifiers, what he settled on worked, the swing box was born,

    a bunch of copycats started making similar amplifiers using the same techniques & selling them to folk with stock voltage systems,

    sadly all was not efficient for these stock volt customers, they did not have external regulators with 18-21v+ of alternator voltage to play with, they were stuck on stock voltage with shitty efficiency,

    nobody seemed to care that the typical clone class C 2 x 2879 these guys were selling only have about 10db gain & draw far too much current for the output they make when compared to amplifiers designed for stock voltage,
    They don't get anywhere near to the efficiency of the correctly load matched single ended circuit used in the datasheet,

    not happy with selling 2sc2879 amplifiers with dismal efficiency some folk started building amps using different transistors with the same philosophy,

    1, 2, 4, pills were easy to copy but how the 6 pill and upwards were tuned was a mythical process a cross between trade secret & black majic performed by secretive fellows all trying to squeeze the last drop of RF from their pills,

    over the years countless 2sc2879's were destroyed, pushed beyond some parameter for too long letting out the smoke, most of these clone builders would struggle tuning a banjo,

    occasionally somebody will ask why their amplifier draws way more current than they expected.

    THE END.
     
  5. Beetle

    Beetle Sr. Member

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    Banjos can be TUNED??
     
    jessejamesdallas likes this.
  6. bob85

    bob85 Supporting Member

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    yeh, the strings & intonation, they just don't sound in tune when they are :D.
     
  7. bob85

    bob85 Supporting Member

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    543,
    I never read the whole thread over there until now,
    Tom had me laughing with his 2879 test, and only 18v there's room for improvement.
     
  8. rabbiporkchop

    rabbiporkchop Well-Known Member

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    You can squeeze more out of them when they are matched.
    received_1721453417910922.jpeg
     
  9. Onelasttime

    Onelasttime Well-Known Member

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    Yes well do not confuse a not so appealing sound with lack of quality or poor design. Banjo's, Bag Pipes, Clarinets etc....are an acquired taste! LOL Piano's are not perfect with regard to tunning but when properly tuned they are in tune with themselves!

    I play brass lipreed instruments aka Trumpet, Flugelhorn, Euphonium, Tuba etc....
     
    Tallman likes this.
  10. rabbiporkchop

    rabbiporkchop Well-Known Member

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    Proper heat dissipation makes a huge difference in performance also. Notice Toshibas flaw? Takes a bit of honing to fix the issue before installation.
    1521932237495.png
     
  11. bob85

    bob85 Supporting Member

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    i find its not just Toshiba, motorola & sgs are almost always distorted when i get an amp in for repair too,
    when they are new they are pretty flat but when they have had some FM hammer the tab becomes concave so only the outer edge of the tab is in contact with the heatsink,

    i lap them with various fine grades of wet & dry paper on plate glass.
     
    BBB, 543_Dallas, LeapFrog and 3 others like this.
  12. Onelasttime

    Onelasttime Well-Known Member

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    Assuming you drive a vehicle with a stock electrical system it is not what you see in 99% of builders workshops! LOL

    Have you taken the time to read Toshiba's data sheet aka White Papers? That is it's power output! Anything else is just ignorant rednecks doing stupid things with a cheap meter that is summing all power at all phase angles and freq. with in it's range!

    So since you can clearly use a computer how about using google and finding the Toshiba white paper's in .000037 Seconds!

    It is really a secret you see ignorant Hillbillies that are also 32nd Degree Free Masons have sacred knowledge handed down from Hiram Abiff that allow them to take advantage of zero point energy using a Toshiba 2SC2879 bjt. In fact Toshiba had to stop making these because the Masons where afraid people would start to open secret sacred portals to the after life and extract free energy which would allow Buba to transmit on 38LSB to Mars and back. Any water in the surrounding area would also spontaneously combust freeing the world from fossil fuel.

    You see Toshiba did not have the sacred knowledge handed down from Albert Pike like Bell Labs did. Alan Holden secretly used Mason teachings to grow crystals for transistors. Toshiba did not have this secret knowledge which is why it took them so long to catch up to the USA post WWII in semiconductors. The demons in Shintoism are not as powerful as the Demons in Free Masonry.

    The problem was to get cost down for the New World Order they had to come up with uses for the transistor to make production affordable. So they had to build in flawed science and circuit design so the masses would not be over whelming the spirit world and other dimensions with traffic. Also those not traveling had no right to know secret sacred knowledge. So while transistors are real and work the applications taught to the world are only 1/1000th as powerful and efficient as they are with the truth. So select redneck key-down and Super Bowel user's are secretly using the truth of this world and Masonic idea to generate a lot more power idea's far beyond the +1 and "So above, So bellow!". You see chemistry and electronics are just watered down Alchemy missing their esoteric component. The best Toshiba Amplifier designs are contained in the secret Albert Pike Archive in the Grand Lodge in Washington DC.! Also the secret archives in the Vatican, I was just discussing Class E amplifier designs with Pope last week!

    The pedophile networks use old 1980's Cobra 19 AM only radio's specially modified with this sacred knowledge to talk world wide. They send signals that are resonate with the Aether using quantum entanglement.They can also transmit to the Mars using just 4 watts of power since they just need to excite the Aether around them and it will instantly alter the Aether any where else in the universe!!
     
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  13. tba02

    tba02 WOOF

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    Man, somebody must have spiked my beer.
     
  14. dave457

    dave457 Well-Known Member

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    Just somebody who's ignorant
     
  15. LeapFrog

    LeapFrog Sr. Member

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    " The demons in Shintoism are not as powerful as the Demons in Free Masonry. "
    :coffee: I need more coffee after reaching this thread!
     
    #15 LeapFrog, Mar 25, 2018
    Last edited: Mar 26, 2018
    Tallman and rabbiporkchop like this.

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