What kind of Oscillator?

Discussion in 'General Electronics Chat' started by Neptune, Jan 14, 2014.

  1. Neptune

    Thread Starter New Member

    Dec 16, 2013
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    I need to build an RF oscillator that has the end goal of around 300W minimum. I'm thinking of tube-amplifying a crystal oscillator but I don't know much about tube amplifiers and whether to use push-pull or class A. Also, what cheap tubes could pull this off?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    The tubes might be cheap, but your legal bills won't be. I think some folks will not be happy when you turn on a 300W radio transmitter.

    What frequency are you working on?
     
  3. Neptune

    Thread Starter New Member

    Dec 16, 2013
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    5 MHz, it's not a transmitter.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    How is it not a transmitter. The RF has got to go somewhere. If not it will likely destroy your output stage.
     
  5. Neptune

    Thread Starter New Member

    Dec 16, 2013
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    I believe Faraday cages were invented sometime ago.
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    tube amps require high voltage supplies. at 300 wats out, quite a bit of current too.how about solid state amp? more current, but probably some of the circuits in the motorola solid state manuals would work. still, without knowing the use of the rf coming out, it would be hard to design for. for instance, an rf heating source has to be tunable to compensate for the change in load with the materials to be heated.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Being a Ham, I am familiar with high-power RF amps. I own one (Ameritron AL-80B) that puts out ~850Wpep; it uses a single 3-500Z triode with about 2200V on the plate. It would put out 400W or so continuously. It requires about 65W of drive. Tuning range on all these amps is 3.5MHz to about 30MHz.

    The other (Collins 30L) uses 4ea 811As. It puts out about 600Wpep and would put out ~300W continuously. Requires about 50W of drive.

    I have another el-cheapo one that uses 4ea horizontal sweep output tubes from an old color TV set. It runs 300Wpep, but I expect that it would be capable of only a 100W continuous.
     
  8. Neptune

    Thread Starter New Member

    Dec 16, 2013
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    It's being connected to two electrodes to accelerate ions I have between the electrodes. I could settle for ~100W. What is the cheapest way to get that?
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    At exactly 5 MHz. its hard to say. If you can work with one of the amateur bands then an amateur radio transmitter can be had for $400 or so.
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    ost of the good ham amplifiers will tune to 5 mhz. the older crystal controlled ham transmitters will probably tune there too. 5 isnt that far from 4 mhz, and they had very good tuning range on their otput matching tanks.
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    Except most modern, non-homebrew ham transmitters, will not transmit outside of the ham bands. One of the downsides of the nanny state.

    There are discrete channels in the 60M band that might work for CW and PSK31
    Channel 1: 5332.0 kHz
    Channel 2: 5348.0 kHz
    Channel 3: 5358.5 kHz
    Channel 4: 5373.0 kHz
    Channel 5: 5405.0 kHz
    or these for SSB
    Channel 1: 5330.5 kHz
    Channel 2: 5346.5 kHz
    Channel 3: 5357.0 kHz
    Channel 4: 5371.5 kHz
    Channel 5: 5403.5 kHz
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
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    Use one of those TTL oscillator cans with a logic level MOSFET on the output - the MOSFET drain can drive the cathode of a grounded-grid power tube.

    IIRC a typical horizontal sweep tube needs about -27Vgs cut off, probably about 500mA to drive the cathode - there's no current gain, so if you need more current - use a bigger tube.
     
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