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10515Re: [loopantennas] Trask Amplifier for Wideband Active Loop Amp - mod suggestions?

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  • Chris Trask
    Feb 24, 2014
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      >
      >>
      >> >
      >> >Well, my bulk buy of BC549C's has arrived, so one more question before I get started on the amplifier...
      >> >
      >> >How closely do I need to match the transistor pairs? Can I just go by HFE reading on my cheap digital
      >> >multimeter, or for best results do I need to break out something a bit more serious? If so, what exactly? :)
      >> >
      >> >Can I just use my 8405A and check that there's exactly 180 deg phase and equal amplitude on each side?
      >> >
      >>
      >> I never did go to the trouble of determining if hfe imbslance affected the performance, and it's less
      >>important for common base amplifiers than it is for common emitter. But, my feeling is that a match of 5%
      >>or less would be prudent.
      >>
      >
      >Thanks Chris.
      >
      >I've just started winding the transformers. I've only got AWG30 wire rather than AWG32 so I've had to use 2873000202 instead of 2873002402 as I an't fit 4 turns of it on the smaller core. Hopefully I can cram it all on the board I'm using.
      >
      >I still have to sort out some low ESR caps, but I've pretty much got everything I need to build one, finally.
      >

      Go for it! In case you're interested, there's a seller on eBay who is selling the MPS6521 at pretty reasonable prices. I bought two lots of 25 for $10 each from him, which will satisfy my needs. They're basically a 2N2222 with twice the current gain. It's a shame that they were never made in SMT so that they might still be available.


      Chris Trask
      N7ZWY / WDX3HLB
      Senior Member IEEE
      http://www.home.earthlink.net/~christrask/
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