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    Power tetrode/pentode tube with internal triode?

    Hi, I am trying to build a small HF CW HAM transmitter. A single tube is desired.
    It would be nice if a power tetrode/pentode with an internal triode existed, so that one can make a two-stage, single tube powerful transmitter, without the problems associated with self-oscillation.
    Are you aware of such a tube?
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    Re: Power tetrode/pentode tube with internal triode?

    ECL80, ECL82, ECL85 or their 'PCL' equivalents maybe?

    E= 6.3V heater
    P = 300mA heater (for series connection in a 300mA chain, the voltage may vary)
    C = triode
    L = Pentode

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    Re: Power tetrode/pentode tube with internal triode?

    Quote Originally Posted by betwixt View Post
    ECL80, ECL82, ECL85 or their 'PCL' equivalents maybe?

    E= 6.3V heater
    P = 300mA heater (for series connection in a 300mA chain, the voltage may vary)
    C = triode
    L = Pentode

    Brian.
    I was thinking of more powerful terode/pentode. These tubes can output up to 10W of RF power. I was thinking of something like 20-30W.
    Maybe just using a dual power tube and wire one section as a triode?
    Professional engineering is the top, but amateur engineering is more fun.
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    Re: Power tetrode/pentode tube with internal triode?

    You are asking for a high power device and a low power device in one package. I don't think anything like that exists. If it did, I would expect it to be a nightmare to keep stable as it wouldn't be possible to physically isolate the 'in' and 'out' ends enough to prevent feedback.

    You can certainly wire a dual power tube so one side emulates a triode, wire the supressor and screen grids to the cathode but the performance wouldn't be good and you would inevitably waste lots of power in the heater circuit. Also consider thermal effects, that power stage would run very hot, probably not what you want right next to an oscillator circuit.

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    Re: Power tetrode/pentode tube with internal triode?

    Have to agree with Brian, such a queer beast has probably never been made.

    Tubes make excellent transmitter output stages, but you are right about keeping the oscillator and power amplifier separate for isolation and stability.

    I think I would be building a transistor oscillator and driving a tube output stage.
    Simple, and you get the best of both worlds.
    Keep the oscillator running and just key the power stage.
    Cheers, Tony.


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    Re: Power tetrode/pentode tube with internal triode?

    Quote Originally Posted by betwixt View Post
    You are asking for a high power device and a low power device in one package. I don't think anything like that exists. If it did, I would expect it to be a nightmare to keep stable as it wouldn't be possible to physically isolate the 'in' and 'out' ends enough to prevent feedback.

    You can certainly wire a dual power tube so one side emulates a triode, wire the supressor and screen grids to the cathode but the performance wouldn't be good and you would inevitably waste lots of power in the heater circuit. Also consider thermal effects, that power stage would run very hot, probably not what you want right next to an oscillator circuit.

    Brian.
    How about this oldie? 6AD7G
    or this 6AK9
    or even better the 6MF8 (12W plate dissipation)
    Not too powerfull,but one might squeeze 20W out of it CW.
    Last edited by neazoi; 4th October 2016 at 14:38.
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    Re: Power tetrode/pentode tube with internal triode?

    The problem with all of those is they share a common cathode. Your only option would be to ground it to prevent the sections interacting and provide negative grid bias from another source. They are really designed for low frequencies, for example vertical scan amplifiers in TVs where the top frequency is no more then 60Hz. The triodes would typically be used as a sync pulse separator and oscillator or both as oscillators in a multivibrator configuration. You would have to experiment to see if they could be used at higher frequencies but I suspect you will run into problems in the low MHz region when the shared cathode inductance becomes significant.

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    Re: Power tetrode/pentode tube with internal triode?

    Also, those tube types were never that common, and you may have trouble sourcing them these days.

    For a CW radio transmitter, TV horizontal sweep output tubes are probably the best choice, because they are made to pulse high currents and have robust heaters and cathodes that will supply the required high peak emission.
    They were also very widely used types, and should be much easier to come by.
    Cheers, Tony.



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    Re: Power tetrode/pentode tube with internal triode?

    ... and even more difficult to find a socket for them :)

    Brian.
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