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Re: Tube coil ideas

Edwin....   I think that the way the tube should be run...like a switch not 
like an amplifier (class b)  As a switch the tube acts like the spark 
gap.  The YC-156 I am selling is rated for pulse service at 64 amps....but 
that is only on a few microseconds and off some period of time as the plate 
dissipation can not exceed 5000w.   The tube will be in cutoff with a grid 
voltage of about -100.  Easy to generate with an isolation transformer and 
a diode and cap.  A transistor switch to change the bias from -100 to say 
-5v will work.
Frequency of the turn on/off can be done with a 555 timer or the like.  A 
pot can be used to adjust the frequency to tune the coil.

Norm


At 11:37 AM 2/13/00 -0700, you wrote:
>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 ??????
>
>     Edd.B