ad: hrd-2

2sc2879 producing 250 watts hahaha

Discussion in 'General Technical Questions and Answers' started by WG3U, May 17, 2010.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: l-BCInc
ad: Subscribe
ad: l-assoc
  1. WG3U

    WG3U Ham Member QRZ Page

    On another forum, there is a guy claiming that a 2sc 2879 can produce 250 watts on the fundamental freq. at 18v for more than a few seconds. I told him he would blow it apart.... Isnt there a video showing this somewhere so I can shut this guy up? I dont have the time or money to make a jig and show him on the specan it not possible, let alone 2879s are $30 now.
     
  2. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    Toshiba transistor eh?

    Just print and give him a copy of the spec sheet and let him argue with the facts as they are presented by the manufacturer.

    http://www.rfparts.com/pdf_docs/2SC/2SC2879.pdf

    You might suggest he should call Toshiba and inform them to change their data to reflect his information as soon as possible.

    Kind of reminds of the fishing stories I used to hear. How big was that fish you caught again?

    My Best,
     
  3. N8YX

    N8YX Ham Member QRZ Page

    A Top Fuel hemi engine can produce upwards of 6000hp from less than 500ci displacement...




    ...but not for very long.

    Some of these folks fell asleep in high-school physics class and never woke up.
     
  4. ZL1UZM

    ZL1UZM Ham Member QRZ Page

    Why are you wasting your time with a fool?
    I wouldn't even raise my eyebrows.
     
  5. W8JI

    W8JI Ham Member QRZ Page


    Better be careful in arguments like that. Data sheets, especially poor ones without much data like the Toshiba sheet, and not absolute limits. All the data in the Toshiba sheet linked is for linear applications.

    I haven't specifically operated a 2SC2879 at absolute maximum output, and the data sheet linked from this thread gives no indication what that might be in deep class C. It only lists linear AB service, but it is a 250W dissipation device. At 50% efficiency that is 250 watts output, and a deep class C operation might push that device to 60% or more efficiency.

    I designed a medical RF device that ran two MRF-150's at 1200 watts output pulse in class C operation. They went to get them manufactured and Henry Radio told my client it would never work based on linear operation SSB data sheets. They came back to me complaining, and we tested and ran several units for MONTHS under all load conditions from short to open at full power. Hundreds of units were built and not a single unit failed even after several years of field use.

    At Prime Instruments we used a very tiny FET the size of a 3N3904 to switch several amperes of pulse at 150 volts in assembly line device to charge meter movement magnets. It would never come close in linear duty, but in hard off-on switching it was fine.

    Don't think a data sheet, especially one lacking so much data as the one linked and only listing SSB linear tests, is an absolute limit for all modes.

    If you wanted to bet him based on it being linear, that would be one thing. If it was based on raw output with no regard to distortion or conduction angle (class) he could easily be correct.

    73 Tom
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page


    Aren't ALL "CB" amps operated in Class C anyway? (With exaggerated ratings as well?) They (usually) don't want "no stinkin' linearity," anyway.
     
  7. WG3U

    WG3U Ham Member QRZ Page

    No, he is saying 250 watts continuous
     
  8. KI6USW

    KI6USW Ham Member QRZ Page

    No; they are not all class C amps. Texas Star and a few others make the class AB biased amps as well. They lack tanking/filter circuits, voltage regulation, and so on. One often thinks of CBers as AM operators primarily. This is a myth that is only partially true. The serious CBer today runs SSB, horizontal beams, filters, and often no amps at all. Some run HF radios so that they run a very clean signal output as well..
     
  9. VE1IDX

    VE1IDX Ham Member QRZ Page


    Can't class C operate continuous duty? FM broadcast TX's do it all the time. :rolleyes:
     
  10. N8YX

    N8YX Ham Member QRZ Page

    Not a good idea to do using an amplitude-modulated signal as a driving source.
     
Thread Status:
Not open for further replies.

Share This Page