SB-200 and IC-746 Pro - Tuning up - confused.

Discussion in 'Amateur Radio Amplifiers' started by KB2FCV, May 16, 2011.

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  1. KM1H

    KM1H Ham Member QRZ Page

    Youve made your point clear ad nauseum, stop already, youre starting to sound like Rich:D.

    Since when did we magically jump from using .01 caps as an ideal choice to suddenly grounding the grids or did you also forget this is a SB-200 and not a 220? There are already a couple of web pages on completely rebuilding the 200 but thats way out of the scope of this thread which has already drifted from the OP question.

    And since when did Orr get involved with the 200? The 200pf caps were a Collins 30L1 rip off which didnt work well there either. Yes, I know Orr got his nose into the 30S1. Heath should have stuck to the Warrior or Gonset or even an old ARRL HB or SSB manual concept which you followed for the AL-572 and AL-800H. Those old engineers understood their stuff.

    Carl
     
  2. W8JI

    W8JI Ham Member QRZ Page

    At least I don't sound like Carl. :)

    In any amp a direct ground is best, I explained that earlier, but it does require rewiring bias and cathode (no big deal) in the 200 and moving the useless ALC circuit if anyone wants to use it.

    The .01 is nearly as good for RF as a direct ground.

    I don't follow anything, including Orr. Good circuits often look somewhat similar, and a person really has to know exactly how the system works. It is pretty easy to copy mistakes otherwise.

    I was on the receiving end of multiple phone calls from Orr about the Ameritron amps, and later the SB1000 and the planned revisions of the SB200 and a new Heath two 3-500Z amp. An engineer at Heath told me the 200 pF cap came from pressure from Orr to use his "super cathode driven" circuit. My policy is to listen, and see if it makes sense. If it makes sense, then use it if it proves out. Those small mica caps never made sense, and when I reluctantly tested several amps with them in every single case IMD and gain flatness improved when they were replaced with a low RF impedance. The only amp I've seen where that system works as proposed was the Collins 30S1. It was a great idea in that amp, but counter productive in anything that has grid current because grid impedance changes over the RF cycle and with drive power. This means the feedback changes phase and levels, and that is not good.

    73 Tom
     
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