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6v & 90v DC Power supply

Discussion in 'Electronic Design' started by James F. Mayer, Dec 27, 2005.

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  1. I need to generate 6v DC and 90v DC from a 12v DC automotive electrical
    system to power an RT-70A/GRC surplus military radio. I need about 250 mA
    at +6 volts and about 75 mA at +90 volts. I was thinking about using the
    guts from an old battery back up but it would be a bit of a kluge. Are
    there any 90 volt regulators in the 78xx series? How do I get the voltage
    up to where I can get something that I can get the 90 volts from. Getting
    the 6 volts doesn't seem to be a problem. A 7806 off the battery should
    work for that unless any of you can see a problem doing that. Maybe the
    common common would be a problem. Right now I'm running it off of an HP6299A
    and an HP6236B with commons jumpered. I'd like to be able to go portable
    with it.
  2. Joerg

    Joerg Guest

    Hello James,
    You can build a step-up or flyback with the LM3478. Tough to solder
    though, it's a TSSOP package. Don't know what current you need but just
    pick a suitable FET.

    For 6V I'd use a buck regulator instead of wasting 50% of the energy in
    a series regulator.

    Regards, Joerg
  3. Bill Turner

    Bill Turner Guest



    I'd use one of those small inexpensive inverters which put out 120vac
    and then use a conventional transformer/rectifier system. You can pick
    up the inverter at any truck stop.

    73, Bill W6WRT
  4. Highland Ham

    Highland Ham Guest

    I'd use one of those small inexpensive inverters which put out 120vac
    Those 'inexpensive inverters' might need some attention in respect of
    the 'hash' they create , possibly causing interference in the receiver.

  5. Fred Bloggs

    Fred Bloggs Guest

    90V @70ma is only 6.3W and a step-up of no more than 90/12=7.5. This
    would be something like a 24VAC center-tapped transformer turned
    backwards with a multivibrator drive of the secondary at 50-60Hz and the
    usual primary is rectified and capacitor filtered to produce the 90V.
    Since the reflected current is only about 1/2A, you can then feedback
    the rectified HV to drive an error amp that regulates the center tap
    down to 9V or so.
  6. Hello James,
    Speaking as a cheapskate ham/hobbyist, how
    about salvaging parts from a computer power supply.
    Find a dud power supply for free at computer
    shops/dumpsters/rubbish tips/roadside etc.
    Salvage the TL494 integrated circuit that can
    be found in many computer power supplies.

    You could build a 90 Volt power supply as
    Ray Robinson has down here

    Here is a link to the TL494 Data sheet

    This link tells you how to use the TL494 IC

    Use another TL494 in a buck converter for your
    12 Volts to 6Volts power supply module.
    Look at the bottom of this page for more info.
    Your 7806 is probably a better idea, saves a lot
    of messing about.
    you could use the guts of a mobile phone
    car charger. The charger that fits into the
    cigarette lighter in a motor car.
    You can find them in pawn shops for a dollar
    or two. Dud ones even cheaper. Usually
    just a broken connection from rough handling.
    Look at page 7 Figure 10 Step down converter.

    In the few car phone chargers that I opened,
    the IC was a MC34063 and the schematic was
    very similar to that shown in figure 10
    Just change R1 or R2 slightly so that you
    get 6 Volts out.
    You may have to check/change the value of
    resistor Rsc to be closer to that shown in figure 10
    You might even get away with not changing the
    inductor. Try it and see if the original inductor
    works well enough for you.

    A ton of reading, bits and pieces for free
    or dirt cheap.
    What a great hobby, this is James, eh!

    John Crighton
  7. Hello again James,
    I just came across this site while looking
    for something else.
    Look at the the 6V AC from 12 V DC. Nifty!

    Here is another
    You want DC out so you will have to fit a bridge rectifier
    and filter capacitors to the output of the transformer
    just like Harry Lythall's circuit above.

    John Crighton
  8. Bill Turner

    Bill Turner Guest



    True for any kind of inverter.

    73, Bill W6WRT
  9. Bill Turner

    Bill Turner Guest



    Excellent info, John. Thanks!!

    73, Bill W6WRT
  10. Do it the way the original radio did it -- dynamotor. You can still find
    them in the back room at a lot of military surplus electronics junk stores.

  11. Joerg

    Joerg Guest

    Hello Jim,
    But then be prepared for some major restoration. The bearings of a lot
    of these are nearly shot, mostly from sitting in an attic for decades.
    It's like old pond pumps. They run fine for a few weeks and then the
    racket increases, some weird noises appear, things get hot and they
    seize up.

    I restored an old Hammond organ. These generate the tones in a similar
    manner. A motor (plus a start motor) and over a hundred pickup coils on
    the long secondary shaft. 20 hours of hard work got it going again but
    we have accepted the fact that some of the bearings are pretty much over
    the hill. So it needs 2-3 starts to coax it to run without that mild
    screeching in the background. Getting spare parts from a company that
    went out of business 30 years ago just isn't going to happen.

    Regards, Joerg
  12. David Harmon

    David Harmon Guest

    On Tue, 27 Dec 2005 05:58:18 GMT in,
    (John Crighton) wrote,
    So why is the guy from TI showing NTE transistors for the power
    switching? Nothing in the TIP line good enough?
  13. Rich Grise

    Rich Grise Guest

    So, put the cam thingie on some sort of spindle, with some kind of
    depth gauge thingie, (maybe a slide pot and a stick), and map the
    disks, and just make the same waveform from ROM?

    Good Luck!
  14. Joerg

    Joerg Guest

    Hello Rich,
    That has been tried many times. Several rather expensive electronic
    organs have come out claiming to emulate a Hammond. So far the real
    enthusiasts do anything to get their hands on the real thing, knowing
    that there will come a day when the last one croaks. IIRC it was Paul
    Shaffer (the guy who makes the music at david Letterman's show) who
    spent the equivalent of a luxury car to have one restored.

    Regards, Joerg
  15. Probably good enough for his measly 32 volts. I need to modify that
    circuit to work on outputs of 90 volts and 6 volts.
  16. Well, tastes vary, but really! Who wants a music box that makes it
    sound like you're at a skating rink? ;-P

  17. Joerg

    Joerg Guest

    Hello Rich,
    Ok, I am not much of an expert on instruments or music in general. But a
    Hammond organ can fill a living room with a sound that, with the eyes
    closed, you'd think you are sitting in a cathedral. And lots of rock
    bands wouldn't use anything else. That is why a lot of Hammonds have
    been "sawed in halves" so they can be transported to the next gig. You
    could even buy split versions built into professional transport cases.

    Regards, Joerg

  18. They have a Hammond B3 at my church, with the Leslie speaker. There
    is another model Hammond in storage that needs a lot of work. Someone
    had it on their screened in porch and the finish is ruined, but it still

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  19. People like the old Hammond organs like the B3 because the can't go
    out of tune. The mechanical tone generator makes sure of that. They
    only sound like a skating rink in, get this, A SKATING RINK!

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  20. Joerg

    Joerg Guest

    Hello Michael,
    Just make sure that the oiling intervals are religiously kept. If the
    other one still plays be grateful for that. If it's the same model or
    nearly the same keep it. Even if the finish is beyond repair some day
    you might be really thankful to be able to scavenge its tone generator
    once the TG on the other Hammond goes.

    A bad finish is often easy to fix compared to taking the whole machinery
    apart. Ours has a superb finish condition but it had been run dry for
    more than a decade before it was given to us. So the TG is quite worn :-(

    Actually it was so bad that when I was done it gulped almost two cans of
    Hammond oil.

    Some words of caution: The rectifier tube of the amp in the bottom is
    located pretty close to the back and it gets freaking hot. I would take
    care that the organ is never placed against a curtain or other flammable
    material and that nobody stores any stuff behind it. The power cord on
    ours almost crumbled in my hands and when attemting to swap it I
    discovered that this instrument did not have a single fuse. So I made a
    nice box with fuse and IEC connector.

    Regards, Joerg
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