Re: Tube coil ideas
> Original Poster: "Edwin G. Buttell" <edd.b-at-snet-dot-net>
> Tesla List wrote:
> > Original Poster: "David Trimmell" <davidt-at-pond-dot-net>
> > Problem is the ARRL Handbook (although, invaluable), and all "radio" theory
> > goes out the door when designing a "tube coil"... At least that the way it
> > seems to me, a "novice".
> Edd.B writes;
> Let's see if I can start a "new" thread...........
> Just about all of the tube coil designs use the same very old
> close coupled / grid feedback oscillator with a large triode
> in class B service. The efficiency of a typical class B circuit
> is about 60% to 65% ( power in / power out ).
> An 833-A triode with cooling ( fan or blower ) has a plate
> dissipation of 450 watts. With 3000 Vdc at 400 Ma ( .4 Amp )
> power input is 1200 Watts, at 60% eff the power output is
> 720 Watts. 1200 - 720 = 480 Watts plate dissipation, this
> over the max dissipation and the tube will run red hot with
> a shorter life expectancy.
> An NST design with a 15Kv/30Ma transformer has a 450 watt
> output and will have a much better spark discharge, much longer
> and thicker sparks from less power.
> I think we all know that, But ..... WHY.....
> The reason is ( I think ??? ) the NST circuit is a pulse
> discharge circuit, with a very powerful pulse and oscillatory
> ringing in a classic tuned circuit.
> The tube circuit has a sign wave output not a pulse. After
> all it's nothing more than an old fashion "ticker coil" design.
> So what would happen if we pulsed our 833-A example ???.
> A variable oscillator with a saw/tooth output from ... say
> 50Kc to 200Kc driving a voltage amp ( 6L6 ) biased AB1 to a
> power amp ( 2 / 6L6 ) biased Class C .... this is how we change
> from a saw/tooth to a pulse. Next is a driver stage having
> about 25 or 30 watts output, an 807 in class C should do it.
> It's not that complicated, it would be all tubes, nothing
> small and modern to burn up, no tuned circuits in the amp
> or driver and with the 50% duty cycle that we obtained by
> pulsing the 833-A ( which is now biased class C ) a higher
> input power can be used without exceeding the max plate
> dissipation. The last benefit but certainly not the least
> is the efficiency of the pulsed 833-A , it will be or should
> be 90% or better.
> Comments anyone ??????
You still can't beat the trick of storing a lot of energy in a cap and
dumping it into a coil.