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High Voltage Components from microwave ovens

Discussion in 'Electronic Repair' started by Albert, Jun 24, 2004.

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  1. Albert

    Albert Guest

    Are old high voltage components from microwave ovens useful, or should
    I chuck them out in the trash?

    I have several transformers that look like they are good for quite a
    few watts of power, some of the high voltage diodes and several
    blowers. I've been saving them.

    Can they be used for power supplies for rf transmitters? Are the
    blowers any good for cooling large tubes in transmitters?

    Thanks,

    Al
     
  2. W3JDR

    W3JDR Guest

    Some years ago, there was an article in one of the ham mags about converting
    microwave ovens into high power microwave ham transmitters. It might give
    some helpful background info. Unfortunately I can't remember the timeframe
    or which mag ran it. Maybe someone else in the group can remember???

    Joe
    W3JDR
     
  3. The transformer is good for 1500 to 2500 VRMS at 0.5 A or more.

    More info at:

    http://www.repairfaq.org/sam/gadget.htm#gadmot

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  4. Theo

    Theo Guest

    I would check to see if these transformers are continuously rated, I seem to
    recall they are rated for intermittent use only.

    Theo
     
  5. Tim Wescott

    Tim Wescott Guest

    They are also built to have high leakage inductance, for current
    limiting when you put your steel coffee cup in there. This is done by
    having physically separate windings and a laminated-steel wedge in the
    window in the core. You have to knock that wedge out.

    There was an article in QST or QEX about using microwave parts to build
    power supplies for linears. Very interesting. Very scary, considering
    that the author also used old refrigerator drawers as the case...

    I saved the pieces from my old microwave in case I ever want to build
    something that puts out more than 5W.
     
  6. Well, microwave ovens can run for hours at full power so I guess that
    rates continuoue? :) It is true they may NOT be continuous rated at
    low or no load due to core saturation.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  7. Wim Ton

    Wim Ton Guest

    Of course you can use the diodes and the capacitors ;-)
    There are some articles on th Internet about converting the transformer for
    a spot welder.
    A also saw an article on using the magnetron as a PLL like amplifier to put
    out 1kw at 13 cm. I can forward the link if you want.

    Wim
     
  8. Joerg

    Joerg Guest

    Hi Tim,
    Just curious: Do people still build linears with tubes and HV supplies
    or is it much cheaper now to use transistors? Mine were all tubes but
    that was about 20 some years ago when FETs and BJT were just way out
    there in terms of cost.

    Regards, Joerg
     
  9. Dave Platt

    Dave Platt Guest

    Just curious: Do people still build linears with tubes and HV supplies
    As one example: Ameritron builds solid-state ham-band amplifiers of up
    to 600 watts output (their "ALS" series). Starting at the 600-watt
    point, and going up to the 1500-watt legal limit, Armitron's amps are
    all based on tubes. There are legal-limit HF amps which use only a
    single tube (e.g. a 3CX1500A/8877 triode, running at about 2500 volts)

    According to a talk I saw recently, commercial television broadcasters
    have moved almost exclusively to solid-state RF amplifiers for their
    newer stations. No one set of transistors can provide thenecessary
    power, so the amps use a large number of smaller modular amplifiers
    operating in parallel - I think the basic "brick" we were shown was
    capable of a couple of hundred watts. I haven't seen any ham-band
    amplifiers using this modules-in-parallel approach, although I'm
    sure one could be built.
     
  10. Joerg

    Joerg Guest

    Hi Dave,

    Thanks for explaining. 600W is pretty good power already. Since the commercial amps are bricks it seems they must have good protection against sudden mismatches as well.

    I remember when I had a coil in the antenna open, which was immediately followed by an exploding coax cable portion. The tubes didn't even flinch but in the 70's just the opening coil would have immediately destroyed even a small transistor amp because the SWR network wasn't fast enough to shut it down.


    Regards, Joerg
     
  11. Guest

    The transformer is good for 1500 to 2500 VRMS at 0.5 A or more.
    Several years ago, while driving from Kansas City to Manhattan, KS (about
    130 miles) I had an interesting QSO most of the way with someone who said
    his amplifier was powered by two microwave-oven transformers (two are
    used because the high-voltage winding is usually connected to "ground"
    internally).

    --Myron, W0PBV.
     
  12. In broadcasting, the station is usually operating on the same
    frequency all the time, so simple Wilkinson dividers/combiners (which
    are frequency specific) can be used, which effectively isolates the
    modules from each other, when one module fails.

    However, a ham linear amplifier is typically required to operate in
    the 1.8-30 (or -54) MHz frequency range, which complicates the
    divider/combiner issue.

    Paul OH3LWR
     
  13. Albert

    Albert Guest

    Yes, please publish the link Wm, and thanks.
     
  14. I suppose this is kinda OT but tubes (usually, klystrons or various
    modifications thereof) are still generally used for high power at UHF.
    IIRC solid-state UHF transmitters are available up to about 30kw or so,
    but larger stations require as much as 110kw to achieve the desired
    effective radiated power.

    Tubes do indeed seem to be a thing of the past at VHF, where powers
    beyond 50kw are generally not necessary.
     
  15. Bill Turner

    Bill Turner Guest

    _________________________________________________________

    They'd be good for a medium power amplifier, but if you're going to all
    that trouble you might as well do it right and go for the legal limit.
    I guarantee you the day will come when you can't quite get that rare DX
    to copy your call and you'll sit there wondering if another db would
    have made the difference.

    Don't ask me how I know. :)
     
  16. Wim Ton

    Wim Ton Guest

    Hi, I lost the link and the newsserver did not like the 1.3 Mb pdf I
    attached. Please mail me and I send it directly to you .This is my real
    address as the account is spammed anyway :-( The article is not findable
    with a search engine, I stumbled upon it.

    Wim
     
  17. Wim Ton

    Wim Ton Guest

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