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Re: Pulsed Tube Coils




On Mon, 13 Jan 1997 22:25:14 -0700 Tesla List <tesla-at-poodle.pupman-dot-com>
writes:
>> Subject: Re: Pulsed Tube Coils
>> >> Subject:       Re: Pulsed Tube Coils
>> >> Subject: Re: Pulsed Tube Coils
>> >Subject: Re: Pulsed Tube Coils
>
>Subscriber: rwstephens-at-headwaters-dot-com Mon Jan 13 21:42:02 1997
>Date: Mon, 13 Jan 1997 00:46:44 -0500
>From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Pulsed Tube Coils
>
>> Subscriber: wb8jkr-at-juno-dot-com Sat Jan 11 10:42:29 1997
>> Date: Fri, 10 Jan 1997 06:52:28 EST
>> From: Mark S Graalman <wb8jkr-at-juno-dot-com>
>> To: tesla-at-pupman-dot-com
>> Subject: Re: Pulsed Tube Coils
>> 
>> 
>> On Thu, 9 Jan 1997 22:39:01 -0700 Tesla List 
><tesla-at-poodle.pupman-dot-com>
>> writes:
>> >> Subject:       Re: Pulsed Tube Coils
>> >> Subject: Re: Pulsed Tube Coils
>> >
>> >Subscriber: rwstephens-at-headwaters-dot-com Thu Jan  9 22:35:31 1997
>> >Date: Thu, 9 Jan 1997 22:07:41 -0500
>> >From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
>> >To: tesla-at-pupman-dot-com
>> >Subject: Re: Pulsed Tube Coils
>> >
>> >> Date:          Mon, 6 Jan 1997 22:43:07 -0700
>> >> From:          Tesla List <tesla-at-poodle.pupman-dot-com>
>> >> To:            Tesla-list-subscribers-at-poodle.pupman-dot-com
>> <SNIP>
>> >I have had plans to attempt voice modulation of the output 
>lightning 
>> >storm from a disruptive discharge TC for some time now and know 
>> >exactly how I'm going to attempt it once I finally 'get a round 
>> >tuit'.  For now I'll only share that my proposed technique 
>recognizes 
>> >Niquist's Theorem for audio sampling rate and will necessarily 
>employ 
>> >a rapid rotary break to sample the audio spectrum where most energy 
>
>> >in human speech is concentrated.  This should produce an amazing 
>stage 
>> >effect.
>> >If 'Man or Astroman' can receive these waves I'd like to hear from 
>> >you guys.  I might be able to build a TC for you that will not only 
>
>> >allow you to communicate with your home planet, but do a neat stage 
>
>> >show here on earth as well!
>> >
>> >If anyone ever picks up one of my modulated TC experiments and can 
>> >prove it I promise to QSL!
>> >
>> >rwstephens
>> >
>>   
>>   Robert,
>> 
>>   Thats pretty much what I was originally talking about,
>> using a transistor switch in the cathode return of the
>> tube turned on and off at a audio rate, with a filtered
>> DC plate supply. Anyway, I just wish I had time to play
>> with half the stuff I think about.<G>  Plate modulation
>> would be a heck of a nice way to go, but I don't have
>> 500 or so watts of audio available or a suitable modulation 
>transformer.
>> Maybe a good way for a high power tube coil to be modulated would be 
>to
>> do it at
>> the screen with a tetrode like a 4-400 or a 813.
>> 
>> 
>> 			Mark Graalman 
>> 
>
>Mark,
>
>If you want quality modulation with low audio driving power, give 
>screen grid modulation using a modest audio output transformer 
>backwards driven from an audio amplifier a try.  With your idea of 
>transistor(zzzzzzz) in parallel in the cathode circuit you are still 
>going to have to create what is effectively that 500 watt or whatever 
>audio power amp, only this time it will have to be class-A (ouch).
>The 813 tube sounds like a good one to start with.  It is really easy 
>to melt the screen grid on a tetrode (you really should install RF 
>bypassed 
>milliamper meters on all your grids and cathode circuit when 
>breadboarding something like this and watch those grid currents).  I 
>melted the
>screen in a NEW 4CX10,000D Eimac tube because I didn't bother with 
>enough
>meters while breadboarding a cluged together circuit and I'm not very 
>pleased 
>with myself as a result. : (  I also DON'T LIKE TETRODES much now (go
>figure).   At least in a toob like the 813 you can SEE if you are 
>thermally 
>stressing the elements, often early enough to shut down power and save 
>the tube.
>
>Oh, another thing about tetrodes.  NEVER allow the screen grid to 
>have accelerating voltage on it with plate voltage absent.  The 
>screen will look like a plate to the electron stream and turn to 
>vapor really quickly.  If your screen supply is just a resistive tap 
>from 
>the plate supply that is an acceptable design practice as both 
>elements will be powered up simultaneously.  If there are separate 
>power 
>supplies, relay logic or other protection circuits are necessary to 
>prevent the application of screen potential before there is nearly 
>full plate voltage.  I know this rule well and it was not the cause of 
>my own 
>meltdown however.
>
>BTW, you might try half a neon sign transformer as a plate modulation 
>transformer for a low powered tube coil.  Insulate the case and run 
>it to your B+ supply.  Run the highest impedance output tap you have 
>from
>your audio amp into the 120 volt winding on the neon.  If you have a 
>70 volt line 
>tap that would be terrific.  Make sure one side of your audio amp 
>output is a good ground.  If the B+ arcs internally in the neon from 
>the core to the primary winding you dont want it taking out your 
>amplifier. I would always feel more comfortable doing such 
>experiments with a vacuum tube hi fi amplifier with its own isolating 
>output transformer built in.  I haven't tried a neon and suspect the 
>results will be rather poor but mention it in case you have one at 
>hand.  I have actually tried this trick with a HV plate transformer 
>and it worked
>quite well.  Put the HV winding in series with the filtered DC plate 
>supply.
>Be sure to run a protective spark gap across the HV winding if you 
>can, and at
>the very least a small value ceramic disc or mica cap good for maybe 5 
>kV at
>0.001to 0.01 mfd to keep RF out of the transformer.  
>
>Good luck.
>
>rwstephens
>   

  Thats a hell of a good idea, man I've got to get the
junk out of the shop and get back to work, thanks for the
input!!

  I have a pair of 572-B's and a pair of 813's and a pair
of 3-500Z's, I really don't want to use up a pair of
3-500 in a coil system, I think I'll start with the 572-B's.  BTW, incase
anyone isn't familar with a 572-B
it is basically a heavy duty 811-A, about an inch taller
and the same diameter and base style. They are rated at
2750 volts for the plate at 275 ma plate current, and
160 watts plate dissipation, the filament rating is the
same as a 811-A 6.3 volts at 4 amps. And they also have a
graphite plate structure.


			Mark Graalman