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  1. #1
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    Using triode tubes as diode tubes for rectification

    Hi,
    I am building a small AM TX attached.
    I would like to replace the diodes with tube rectifiers (semiconductor-free), whereas I need to keep the power transformer simple (no center tap).

    There as three options without a center tap, I am aware of:
    1. A half wave rectifier (too much ripple)
    2. A full wave bridge rectifier (it must use 4 tubes)
    3. A full wave voltage doubler (it uses just two tubes)

    I like thw 3rd option, but there are no dual diode rectifier tubes, with separate cathodes, that can provide around 27mA or so for both sections of the 6cq8. So I have to use two separate tubes.

    Now, I am thinking if a dual triode tube, can be used for the purpose, like the ecc83 etc. If so, how should the grids be connected (just left them floating?)
    If this can work, how about use their grids for regulating the HV as well, this will double their use.

    Please let me know if my thoughts are correct. Any available information on the topic?
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!

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  2. #2
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    Re: Using triode tubes as diode tubes for rectification

    Connect the grids to the cathode directly.
    One thing of concern, though, as both heaters are not independent and will be electrically connected together, that you do not exceed the cathode-heater breakdown voltage.

    This thread should be moved to the retro - electronics area.
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    Re: Using triode tubes as diode tubes for rectification

    Quote Originally Posted by schmitt trigger View Post
    Connect the grids to the cathode directly.
    Don't you think these triodes will drop a lot of voltage? Rectifiers are designed to minimize the series loss. However, only 165v are needed and the voltage doubler with the back to back 220v-to-6.3v transformers I am thinking to use, will provide much more than enough headroom for big voltage drop.
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    Re: Using triode tubes as diode tubes for rectification

    The voltage drop will be quite small but a diode is still a better choice.

    Why are you using 'back to back transformers' ?

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
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    Re: Using triode tubes as diode tubes for rectification

    Quote Originally Posted by betwixt View Post
    Why are you using 'back to back transformers' ?

    Brian.
    two 220v-6v transformers are readily available in most electronics shops. Isolation transformers or HV and/or CT are rarer nowadays.
    Professional engineering is the top, but amateur engineering is more fun.
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  6. #6
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    Re: Using triode tubes as diode tubes for rectification

    Quote Originally Posted by neazoi View Post
    Isolation transformers or HV and/or CT are rarer nowadays.
    I agree with this situation, as I've had to do exactly the same trick and for the same reason.
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