Suitable PA Amplifier

Discussion in 'The Low Bands - 630/2200 Meters - VLF' started by G3YRO, Nov 9, 2017.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    Well let me be the first to start a thread on this new section!

    Although I'm a 160m enthusiast, I don't really have any enthusiasm for these very low bands. It seems it would be a lot of effort to have very few contacts !

    However . . . I have occasionally thought about what I would do IF I wanted to transmit on there. The beauty is that I figure almost any Audio type devices should work fine.

    Firstly, I think I would make a very simple Valve Transmitter, out of a cheap secondhand 100 watt Guitar Amp. . . . free-running VFO on those frequencies would be quite stable . . . so use whatever preamp valves are already in the Amp as a VFO and to drive the output valves - just connect them in parallel and in Class C. Should get nearly 200 watts of RF out.

    If you wanted higher power, and wanted to go solid state, I figure most Audio Amps (1 kW are quite cheap) would work up to these frequencies if you remove the de-coupling inside. You only need less than 1 volt of drive to get full power, so a simple oscillator or DDS would be all you'd need . . . plus your output filtering/matching, of course.

    The beauty of converting any secondhand Audio Amp is that you already have everything you need inside . . . especially the Power Supply.

    Roger G3YRO
    Last edited: Nov 9, 2017
    KA9JLM likes this.
  2. K8JD

    K8JD Ham Member QRZ Page

    My son had a big subwoofer amp for one of his cars, you know the ones that sit behind you at a stop light and rattle your teeth with the Bass notes.
    Anyway, he grew out of that phase of youth and I wonder If it is sitting in his garage or basement, maybe It would work as a Low Freq Radio amp. Why not?
    I have a 40 Amp Astron power supply that would probably power it up here in the ham shack :D
  3. G3YRO

    G3YRO Ham Member QRZ Page

    The only problem with a lot of the Car amplifiers is that they tend to use ICs . . . several of them in antiphase . . . so probably not so suiyable.

    I was mainly suggesting using secondhand Audio Amps as the basis of a rig for these bands, as you already have a Chassis and a Mains power supply, as well as most of the other hardware.

    Surprised there hasn't been more replies to this thread . . .

    Roger G3YRO
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    My SWTPC Tigersaurus 210/A amplifiers (link) work well past 100 KHz. The power bandwidth is specified as 400 KHz (output transistor GBP = 2MHz). The amplifiers are specified to produce 200W into 8Ω or 250W into 4Ω. Hirsch-Houck Labs tested one to 316W at clipping into 4Ω. I built a pair in 1975.
  5. WA3ETD

    WA3ETD Ham Member QRZ Page

    Some folks are using Hafler audio amps, with minimal modifications. Check
    Jay W1VD site for details ... for details...

    John WA3ETD/WG2XKA Part 5
  6. AA4HA

    AA4HA Ham Member QRZ Page

    You can start watching the auction sites for "ultrasonic amplifier". Quite often those are up in to a couple of hundreds of KHz at hundreds of watts.

    Audio amplifiers (like a tube based push-pull) is going to be limited by the frequency response of the audio transformer.
    W1TRY likes this.
  7. N2SUB

    N2SUB Premium Subscriber QRZ Page

    The words "Cheap" and "Valve" do not normally go in the same sentence with guitar amp. Most musicians covet their tube amplifier, and if they are willing to sell will normally want top dollar. If you are looking at a 100 watt amp, that kind of power could set you back a lot, and if the guitar players in your neighborhood found out you used it to make a transmitter, it could get ugly. ;)

    Unlike radios, old (tube) guitar amps increase in value and are highly sought.
  8. W0AAT

    W0AAT XML Subscriber QRZ Page

    TV Sweep tubes(could use oddballs) will work well at these frequencies!
  9. N1BCG

    N1BCG Ham Member QRZ Page

    This is a magnificent site, and it offers probably the simplest do-it-yourself, all-the-power-you-need CW transmitter plan for the 2200M and 630M bands:
  10. N3DT

    N3DT Ham Member QRZ Page

    I see VE7TIL's call sign in that link. He's the guy that found 'IMAGE', the lost satellite last January and has been in the news. This guy must work from audio through microwave.

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