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      CommentAuthorlegendre
    • CommentTimeAug 1st 2013 edited
     
    Posted By: alsetalokinHey, I could use a 2d21 if you've got an extra one. The GenRad Strobotach uses one and I'd like to have a spare.


    Have I ever said no to you?
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      CommentAuthorAngus
    • CommentTimeAug 1st 2013
     
    Get a room.
    • CommentAuthorAsterix
    • CommentTimeAug 1st 2013
     
    Posted By: legendreNaturally, I'm with the gas thyratron crowd on this..


    Before the ittle bitty 2D21 came onto the scene, the workhorse was the 2050. You saw those a lot in control circuitry, and later computer unit-record equipment. I don't know if an 026 keypunch has any, but I suspect that it does.

    I like the idea of using an 884 gas triode in series with a FET serving as a constant-current source for a sawtooth generator.

    But 40KV at "several amps" would likely vaporize the innards of a 2D21.
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      CommentAuthorlegendre
    • CommentTimeAug 1st 2013
     
    Posted By: AsterixBut 40KV at "several amps" would likely vaporize the innards of a 2D21.


    Ha, yes.. I don't have a datasheet in front of me, but I sincerely doubt that a 2D21 would make it 10% of the way up that 40K voltage slope.

    I was just kidding around - though the offer was ultimately genuine! ;-)
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      CommentAuthorlegendre
    • CommentTimeAug 1st 2013 edited
     
    OMG, look at this GR Strobo-tach!

    JESUS FUCKING CHRIST ON A POGO STICK, AL.

    $2000?!
  1.  
    Yep. That's a 1538A, a 150,000 rpm unit, very rare. Mine is a 1531AB which only goes to 40,000 rpm. I paid 600 for mine from Toronto Surplus about 6 years ago and probably got the special deal.
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      CommentAuthorlegendre
    • CommentTimeAug 1st 2013 edited
     
    Posted By: alsetalokinYep. That's a 1538A, a 150,000 rpm unit, very rare. Mine is a 1531AB which only goes to 40,000 rpm. I paid 600 for mine from Toronto Surplus about 6 years ago and probably got the special deal.


    Once again, shows what I know.. or don't.

    I figured all of those 'classic' type GR instruments were boat anchors.. mostly low-value, not really worth the time and pricey parts to set one truly straight in the eyes of god. Anyway, I'm now thoroughly disabused of those beliefs.
    • CommentAuthortinker
    • CommentTimeAug 1st 2013
     
    I have found these guys in Nebraska very good to deal with. Their overseas shipping is expensive, but with a good friend living in Omaha that is not a problem to me. Link is to their current offering of Transmit/Receive tubes- including some Hydrogen Thyratrons.

    http://www.surplussales.com/Tubes-Sock-Acc/A-Z/TubesListed_a-m.html
    • CommentAuthorjoshs
    • CommentTimeAug 1st 2013
     
    Andrew's project involves handling hundreds of thousands of Watts. Even if he is very careful and thrifty, the total expense is likely to approach the cost of a rather nice new automobile.
    • CommentAuthortinker
    • CommentTimeAug 1st 2013
     
    I appreciate 40kV x 2A = Feck! I have no idea what Andrew expects to spend to get there. Or even if he plans to survive the first test. However, I should think that by sticking one output lead in his mouth and attaching the other to his dick he would be able to reconfigure his corpus into plasma easily.
  2.  
    Well, that's food for thought. Anyway, I agree about the Nebraska guys - I got my low loss trimmers for my VHF matching network from there. I should say that the HV spec I quoted was on behalf of a fellow experimenter. I can't say more or else (s)he would have to kill me. Probably using the method prescribed by tinker.
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    Just a side note about higher order time derivatives, which are often attributed almost magical properties by the more whimsical. For a sinewave, these increase in magnitude for each higher order, the multiplicative coefficient being "omega" = 2*PI*frequency. So the Nth order time derivative is omega^N bigger than the fundamental.

    At the birth of the radio era, electrical sinewaves came into general use. Nothing unexpected was seen then, nor has been since, in respect of these Nth order terms. I expect nature has sinewaves of her own too, and they've been going much longer. Like sounds.

    This post may be rubbish. YMMV
    • CommentAuthorjoshs
    • CommentTimeAug 1st 2013
     
    Posted By: Andrew PalfreymanJust a side note about higher order time derivatives, which are often attributed almost magical properties by the more whimsical. For a sinewave, these increase in magnitude for each higher order, the multiplicative coefficient being "omega" = 2*PI*frequency. So the Nth order time derivative is omega^N bigger than the fundamental.

    At the birth of the radio era, electrical sinewaves came into general use. Nothing unexpected was seen then, nor has been since, in respect of these Nth order terms. I expect nature has sinewaves of her own too, and they've been going much longer. Like sounds.

    This post may be rubbish. YMMV
    What am I missing? d/dx(d/dx(d/dx (d/dx(sin(x))))) = sin(x).
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      CommentAuthoralsetalokin
    • CommentTimeAug 1st 2013 edited
     
    Posted By: tinkerI appreciate 40kV x 2A = Feck! I have no idea what Andrew expects to spend to get there. Or even if he plans to survive the first test.

    I actually thought he must be joking when I read the spec at first. Then I decided to take him seriously. If he takes my advice he just might encounter someone who has a "turnkey" system sitting in his garage, or can put one together with only a little trouble. If AP can put up with 10 ns risetime that is, instead of 100 ns.
    • CommentAuthorsonoboy
    • CommentTimeAug 1st 2013 edited
     
    What about a rotary spark gap or air / magnetic quenched? If you need better control it's easy to use a trigger electrode with a guided gap too.
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      CommentAuthorAngus
    • CommentTimeAug 1st 2013
     
    Posted By: joshsWhat am I missing? d/dx(d/dx(d/dx (d/dx(sin(x))))) = sin(x).


    Missing nothing if you counted the "d"s correctly. And even if not, only missing a right angle.
    • CommentAuthorjoshs
    • CommentTimeAug 1st 2013
     
    Posted By: Angus
    Posted By: joshsWhat am I missing? d/dx(d/dx(d/dx (d/dx(sin(x))))) = sin(x).


    Missing nothing if you counted the "d"s correctly. And even if not, only missing a right angle.
    I don't know where Andrew got his funny idea that the derivative of sin(x) or cos(x) yields magnitude gain along with 90 degrees phase shift.
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      CommentAuthorAngus
    • CommentTimeAug 1st 2013
     
    Scaling. d/dt (f(Kt) = K d/dt f(t)
  4.  
    Posted By: sonoboyWhat about a rotary spark gap or air / magnetic quenched? If you need better control it's easy to use a trigger electrode with a guided gap too.

    I thought about that too, but the requirements exceed the capabilities of such gaps, I think. Besides, you would have too much jitter in timing, probably, and it would be difficult to build and maintain. Big tubes are probably much easier to deal with in the long run. But a power supply that can deliver a couple amps peak at 40 kV and 500 Hz-- controllably -- is in itself a large project, not something for your average garage experimenter.
    My personal experience goes up to include a cap-charging power supply capable of 30 kV, 150 mA or so continuous power, and charge-discharge rates of under 10 Hz with TAGs and cap banks up to around 1 uF at those voltages. And it is _scary_ to construct, test and routinely work around such equipment. The blood rushes out of my head when I even think of a 40 kV, 2 amp power supply.
    • CommentAuthorAsterix
    • CommentTimeAug 1st 2013
     
    Posted By: alsetalokinThe blood rushes out of my head when I even think of a 40 kV, 2 amp power supply.


    Get your head in the right place and the 40KV will neatly cauterize the blood vessels, stopping the bleeding from your head.