Heathkit sb-200 how to convert to 811a tubes

Discussion in 'Amateur Radio Amplifiers' started by K5BOO, Sep 4, 2014.

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  1. N2EY

    N2EY Premium Subscriber QRZ Page

  2. N2EY

    N2EY Premium Subscriber QRZ Page

    Thank you, Pete.

    But in this case it's not really about "opinions". It's about hard facts. Engineering of power supplies.

    Simply being an old timer does not make someone right. I have been an amateur 47 years, an Extra for 44. I have BSEE and MSEE degrees from major universities. I've designed, built, repaired and used more ham rigs than I can recall.

    But none of that makes me right about anything. What makes me right is the facts and reason behind what I say.

    Facts, not opinions.

    What would you have me do, Pete?

    Say I'm wrong when I know I'm not? Stop asking for someone to point out my errors when know there aren't any? Not comment when someone uses logical fallacies in an attempt to discredit me?

    Let's get down to what is really going on in this thread:

    I wrote that if you take the SB-200 power supply and convert it to a full-wave-bridge configuration with silicon rectifiers and capacitor filter, the output will be about 1200 volts no-load and about 1000-1100 volts under load.

    Sue says I'm wrong, that the output will only be about 850 volts, based on her recollections of a power supply built over 30 years ago.

    I have not denied her experience with that power supply. But I have claimed that something was amiss in it, because it should have produced over 1000 volts if it were built and operated as described, yet it only produced 850 volts or so.

    I have posted all sorts of data, calculations, analysis and explanations backing up my conclusions. Except for one typo which had no effect on the calculations or conclusions, nobody has pointed out ANY error in ANYTHING I posted in this thread.

    Yet somehow I'm still "wrong". I am told by Sue that I have all sorts of "issues" because I dare to disagree with her.

    Is it somehow wrong to stand up for the facts and sound reasoning?
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    Give it a rest already Jim.
    You might be right, I'll give you that, but look at the noise you have made. over this.
    All this over a minor detail.

    Have a nice life.
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Yep. Textbooks, ARRL Handbook, et al all say that an unloaded fullwave rectifier produces 2.5 x VRMS (1.414 x VRMS). Because the output filter capacitors are in series, a fullwave doubler voltage multiplier produces twice that (2.828 x VRMS):

    Barring significant leakage in the filter capacitors and/or high bleeder current, this'll be just about exactly the case. Testimony indicates an unmolested SB-200 fullwave doubler rectifier PS produces around 2KV. Changing to a fullwave bridge rectifier, I'd expect about half that.

    The numbers you show for a loaded PS seem about right. Losses in the transformer and AC source can easily show that kind of difference between loaded and unloaded.

    vy 73,
    Bryan WA7PRC
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    Which is all I've been saying since the beginning.

    In fact, if one things about it, if a power supply such as used in the SB-200 is rearranged from voltage-doubler to full-wave-bridge, you'll get half the voltage and twice the current - because in both cases the load presented to the transformer is the same! And since it has been repeatedly documented that the stock SB-200 supply will produce at least 2000 volts at 500 mA, if you change it to a full-wave-bridge the output will be at least 1000 volts at 1000 mA.

    Thanks for verifying my conclusions.
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    The way you say it and the your incessant habit of talking down to people is the problem,
    Yes you are right and were right all along.

    Work on your delivery Dude.

    REASTON QRZ Member

    A voltage doubler does not double voltage as compared to a full wave bridge using the same components and load. Voltage doublers usually have excessive capacitance (well beyond diminishing returns) in the filter string trying to keep the voltage regulation close to that of a full wave bridge. The difference between full wave and doubler is enough to be noticeable. Your books should explain why this is so but the short explanation is that current in the transformer and diodes is higher in the doubler and the caps are really being used as rechargeable batteries instead of filters. But caps don't work anything like a high voltage rechargeable battery.

    Most all engineers that design commercial power supplies will avoid doublers if at all possible. They have other problems too. The Henry tuned choke power supplies were excellent but cost much more and that big choke didn't make any easier to carry the amp and power supply around.
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    I disagree. Changing to a fullwave bridge will produce at least 1000000 mV at 1000000 uA. :p
  9. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Keith, I sent you a PM about threw weeks ago stating I had some 572B tubes. Check your in-basket.
    K9DBE likes this.
  10. KM5FL

    KM5FL Ham Member QRZ Page

    Keith has posted only 2 times on QRZ, both times are in this thread.. With 8 pages of useless bickering, I'm guessing Keith has fled the scene and probably won't be back.. :(

    I'll just say -- "Can't blame him", and leave it at that..

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