Yet another L4B rescue

Discussion in 'Amateur Radio Amplifiers' started by W9JSW, Apr 13, 2018.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Your 500-0-500 xfmr even with a doubler can only produce about 2.8kVdc which isn't nearly high enough to hipot most transmitting tubes. A 3-500z is rated 4000V "operating," and should hipot at much higher than that. You'd want about 200-300 Megohms in series with that to limit current. Stuff like this works for that: http://hvstuff.com/240m-ohm-5w-25kv-5-non-inductive-high-voltage-resistor-glass-glaze
     
  2. W9JSW

    W9JSW Ham Member QRZ Page

    How about an open core neon transformer 3500v at 8ma?
     
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    ...getting warmer! :p
    Don't need much current, just HV.
    A doubler on that baby could make a nice tester. You just need to be careful with the rest of the build, and careful with the variac!

    [​IMG]

    Very nice!
     
    Last edited: Apr 19, 2018
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    A multiplier (doubler, tripler, quadrupler, etc) can get you there. If you use half wave topology (link) with one end of the transformer secondary on ground, you don't need to be concerned about transformer insulation. Limit the current to a safe value. Use a Variac on the input to adjust the voltage.



    A furnace ignition transformer (around 10KV at a few mA) is an excellent basis for a hi-pot or breakdown voltage tester.
     
    KM1H and KD2ACO like this.
  5. W9JSW

    W9JSW Ham Member QRZ Page

    Can I borrow one of the transformers from one of my beer signs?
     
  6. W9JSW

    W9JSW Ham Member QRZ Page

    What is the target hipot voltage for the 3-500?
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't recall Eimac (or anyone) recommending one, but I've used 8kVDC.
     
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    Using your 500-0-500V transformer w/ a septupler, you'd see about 1000 x 1.414 x 7 = 9900V maximum The available current is 1/7 x 200 mA (27.5 mA). Use a small Variac on the input to adjust the voltage. You'll want to monitor the output voltage and current.
     
  9. W9JSW

    W9JSW Ham Member QRZ Page

    If I may ask, I will draw up a circuit and can get the group here to help me establish the right values of caps and R for the circuit. I think I understand how to proceed. I like being able to use parts that I may already have. I am not sure what the minimum value of the caps in the multiplier will need to be. I have a mess of electrolytics that have a rating of 350v so I can string them together in the multiplier. I understand that each leg only need to manage 1.4 times the rms value of the trans, right? Also have 30 1N5408 diodes. Have a 50ua plastic meter. That may not handle 10kv...
     
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    The caps you want are more like 1500v film caps. The value doesn’t have to be much because the current is really low. You are going to stack them and rectifiers up to get to the voltage you need.

    Stages that look like this:

    [​IMG]

    ... and really, you don't want big electrolytics here! You would need more stages and the energy stored would be dangerous. :eek:

    Show us your ideas and we'll think out loud about it. :)
     
    Last edited: Apr 20, 2018

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