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Has anybody considered doing this, power a big tube amp with....

Discussion in 'Home Brew' started by Tallman, Apr 17, 2017.

  1. Tallman

    Tallman
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    W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    A microwave power supply? Microwaves are cheap and the power supplies put out a lot of volts and amps.
    It has been a long time since I was inside the covers of one. I was extremely careful because I know how much voltage was in there. Warning stickers all over saying, " Do not try to service, Lethal voltages inside."
    Five thousand volts need to be respected! So I was wondering if any one has considered using one of these cheap monster power supplies for one or two of the EIMAC tubes? I have a microwave getting ready to go belly up and would keep the power goodies out of it and build a new amp with it.


     

  2. ExitThirteen

    ExitThirteen
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    Don't know if the microwave transformer would be able to withstand the current draw needed for the higher output tubes? I'd think you'd need something that could hold up 2A or so if you wanted to run something like a pair of 3-500's...at least have enough there with some headroom. But, I may be off base with that.


    ~Cheers~
     
  3. Tallman

    Tallman
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    Most microwaves run 1000 watts continuous for as long as you have the timer set. Some of the higher end microwaves run 1500 watts or more.
     
  4. 2RT307

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    I remember Captain K talking about doing this with a home brew tube amp. It's been a couple of years back, though... Maybe he will chime in.
    73,
    Brett
     
  5. Tallman

    Tallman
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    I always respect the Captains opinion on tech matters.
     
  6. wavrider

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    it has been done
    google microwave oven transformer for HF amplifier
     
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  7. Captain Kilowatt

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    I was in a discussion about it and looked into rewinding a microwave transformer to use as a high current filament supply but never a plate supply. It has been done but it is a cheap way to do it in every sense of the word. One side of the windings is connected to the transformer case so you have to isolate that. The cores tend to saturate easily and that is by design for use in a microwave oven but not a great idea for use in an amp. Sure a microwave may run continuously but it actually pulses the tube. on and off depending on the power level setting. Even on high they usually cycle the tube on and off. Most amps built around a microwave oven transformer use two or sometimes even three transformers which is really a bush league job unless you live in a third world country where parts are hard to obtain but there is plenty of trash to scrounge from. Just my opinion mind you but I would never use one for an amp project. I prefer REAL iron for a plate supply like this one.:)

    20170102_154002s.jpg

    It looks so much better sitting in the cabinet don't you think? :D

    20170102_153803s.jpg
     
  8. Tallman

    Tallman
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    Great solid advice, thanks Captain Kilowatt.
    I will just toss my old dying microwave in to the recycling bin.
     
  9. BBB

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    Yes. Ditch it and look for something like the others shown.

    [​IMG]
     
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  10. 2RT307

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    Well, I was kinda warm... lol. My memory is getting fuzzy, I guess! Thanks for the info and update.

    73,
    Brett
     
  11. Captain Kilowatt

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    That's OK Brett it happens to all of us. LOL The MOV xmfr did not work out too well as a 16 amp 6.3 vac filament supply for what I was going to build a four tube 572B amp but it's just as well. I eventually decided on a single 3CX3000A7 since a filament xmfr and a tube socket as well as a couple broadcast pulls landed in my lap. The image I posted above was the beginning layout of the power supply. I tested it last weekend. Variac controled 4500 volts with 55uF of non-PCB oil filled caps and rectifiers rated for 22 Kv at 30 amps. :D
     
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  12. 2RT307

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    How much does that puppy weigh? And nice Plus Two mic!

    73,
    Brett
     
  13. Onelasttime

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    I have seen some Russians do it. One has a youtube video of it and to be honest his work scared me to death as he was poking around inside of it.

    I have considered it. You need to have at least 2 of them together in series because they are not center taped.

    If you decided to use 4 of them in series and parallel into a diode board you have to find a way to load share and load balance if you will. That is the real challenge because if you do not you will have one set doing most of the work and that is an issue. The alternative would be to use tubes that are not very demanding voltage or current wise like the 4X250 and 4x150 series they have insane multiplication factor aka gain! Using 4, 6 or 8 of those would be a piece of cake for a MOT. Once you get into the big boys those those guys need not only decent voltage but amperage too.

    I think a more practical thing to do is use them to make 6V-24V supplies all you need to do is knock out the shunt and cut the secondary off and rewind with your choice of wire.

    I made a small spot welder for my oldest son to use in middle school for metal projects. Previous to that all I had was the huge AC/DC Red Tombstone Lincoln Stick Welder with Stitch Welder Attachment in addition to standard electrode holder.

    I have 9 NOS 4X150 tubes. I am thinking about building a 2 tube unit with two MOT's.
     
  14. Captain Kilowatt

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    The lack of a center tap is not an issue. My plate xmfr does not have a center tap and most of them do not except for some older stuff. A center tap is only required if you run a conventional full wave rectifier rather than a full wave bridge rectifier. One side of the MOT is connected directly to the case so you either have to run two in series of remove the connection to the case which makes it a regular xmfr at that point.
     
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  15. Sarasota Slim

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    Some projects are done, just to do. To see if you can do it. Not necessarily because it's the best way to go about it.

    Repurposing parts of a microwave to power an amp sounds interesting. Seems a good way to maintain or improve electrical skills.
     

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