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How to evaluate RF tubes for power and fidelity?
How to evaluate RF tubes for power and fidelity?
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Old 7th April 2010, 07:58 PM   #11
banat is offline banat  Serbia
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Thadman,YES,YES,and again YES.I made so many AM transmitter(low And midlle output power- up to 10kw signal carrier).I Broadcasting on the Am band 1800-2000 Khz illegal so many years together with other Pirat broadcaster(Collegue),which emitting even today.Magic of the MW(Midlle wawe) is greath.First:FREE SPEACH or MUSIC selection,you do hawe responsybity to NO ONE(Listener,goverment,Low or other Broadcaster-NO ONE.Second:YOU chose time and program lenght(When you want to Emit-Emit,when YOU dont want-dont,Free well.Third:Basycly technicly is so simple,beacose freqency is so LOW, up to 2MHZ max.(Here is the rulle:If that DIY Tube MW Transmitter dont work properly from first `turn onn `_Throw hem away thru the window(open) and start to made NEW one . 27 MHZ AM(Amplitude modulation) is quit diferent.First: for that frequency Grounded Grid Class A/AB Linear Operation(unfortunetly Low Eficiency) is Rulle.Second 27Mhz Band sometime is totaly clossed beacose of low Eter propagation so That(slingshot) transmitter can not reach long distance independent from output power.Think half of the year Band is Open and half of the Year is clossed.Third:Antena system and Waweguider is wery complex and expencive when you exced 1KW signal carrier(in MW band I always use simple 2-3mm copper wire,~75m long,betwen two isolator extented(Thats tunned lambda/half,resonant emitter antena independent from RF Power OUT).Yes on that Russian Tubes List You cant Found many wery rugged,suitable and relative CHEAP tips for that purpose,but the Tubes is not the `problemos` but ewerything around the tubes(27 mhz RF Exiter,Huge PSU and Antena System).Best Luck Thadman. Pirattes Forewer and Ewer
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Old 7th April 2010, 08:01 PM   #12
thadman is offline thadman  United States
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Quote:
Originally Posted by kavermei View Post
It's not easy to make a transformer (air core or other) that will handle 225kV... arcs will fly all over the secondary, punching holes in the insulation of the windings...
Don't Tesla Coils use Air Core transformers? I've heard of some designs capable of 1MV.
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Old 7th April 2010, 08:19 PM   #13
thadman is offline thadman  United States
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Quote:
Originally Posted by jrenkin View Post
A long time ago, when I worked in lasers, we had a 50KV transformer made for an experiment we were performing. We had to submerge it in insulating oil and the power wire coming out of it, insulated in one inch of silicone would have blue fingers of electricity radiating from it. Arcing was frequent to anything else. You couldn't point your finger at it from less than a couple of feet. The l;ab smelled of ozone. It is amazing we survived. Truly these voltages need to be in well controlled environments and most home work areas just wouldn't be safe.
What would be the absolute highest voltage you'd consider realistic? The voltage limit will place a constraint on the widest achievable air gap that will support a stable plasma.
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Old 7th April 2010, 08:30 PM   #14
rotaspec is offline rotaspec  New Zealand
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For a power transformer that will produce up to 10kv at 1kw, look for old neon sign power supplies. I had one that could maintain an arc up to 6 inches.
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Old 7th April 2010, 09:24 PM   #15
thadman is offline thadman  United States
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For extremely high voltages, couldn't we insulate the parts within a ceramic structure characterized by an extremely high dielectric strength (ex. Alumina)?

The ceramic insulation could extend all the way to the ends of the electrodes, where the plasma would be created. Would Tungsten be a good choice for the electrode material?
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Old 7th April 2010, 09:56 PM   #16
wakibaki is offline wakibaki  United Kingdom
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I had a hole burned (drilled) in my fingernail by a 12 watt SW military comms radio with an integral antenna tuner. It was cranked to a high impedance match.

I looked at it on the Manta 3D inspection scope. It was like a little volcano, a millimetre or so across, in the middle of the nail. It hurt like billyoh, let me tell you, Old Man, and it didn't get better quickly.

I was a lot more respectful around the 100 and 200 watt radios after that. 'Course it's all down to the impedance, the voltage isn't nearly so high in a 50 ohm co-ax.

Controlling and directing that much energy at these kinds of frequencies is not a task for the unwary. If you're lucky you could get an extremely severe burn, if you're unlucky you could kill somebody else, perhaps a family member.

I have been fairly cavalier myself with respect to safety, I can think of a number of incidents involving e.g. potassium chlorate in admixture, silver acetylide, nitrocellulose and nitrogen tri-iodide which, in hindsight, I have been fortunate to survive with a full complement of fingers, and hearing, for the time being, intact. I never imagined I was risking a burn from a 12 watt radio tho', no matter how survivable it turned out to be.

The good news is that it's not that easy to build a 27MHz anything analog. Other than an oscillator that you didn't want. If 1% if the energy gets loose you'll be a nuisance world-wide on the right day. But of course you won't be hard to find...

w
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Old 7th April 2010, 10:17 PM   #17
bob91343 is offline bob91343  United States
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Shades of Nikola Tesla! He would have loved it.

I remember trying to build a CRT high voltage supply. Drove me nuts, with the corona.
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Old 8th April 2010, 12:00 AM   #18
thadman is offline thadman  United States
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We might enclose the electrodes within a hollow, spherical electromagnetic shield, something possibly the size of a basketball. It would of course be highly perforated to minimize acoustic interference and reflections. The inner surface of the sphere could be made of a conducting material to absorb some of the radiation produced. The outer surface of the sphere could be coated with a ceramic characterized by a very high dielectric strength.

If the amplifier was completely insulated, the outer surface of the sphere completely insulated, connections to the sphere completely insulated and connections to the electrodes (within the sphere) completely insulated, wouldn't the possibility of being shocked be at an absolute minimum? The only surfaces capable of discharging electricity would be the electrodes themselves.

In addition, we might provide the signal to the amplifier digitally via an optical fiber to decouple it electrically from the other electronics (ex. DSP).

Assuming these conditions were met, would it be safe enough for operation by someone not familiar with High Voltage? What would be the Highest Voltage you'd consider realistic (ie not a health hazard) for such a setup?
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Last edited by thadman; 8th April 2010 at 12:03 AM.
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Old 8th April 2010, 12:20 AM   #19
thadman is offline thadman  United States
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As far as cooling for the Vacuum tubes, couldn't we use a dielectric fluid? I've read a few journal articles where engineers used dielectric fluids in a 2-phase liquid-vapor cooling system.

The liquid could be compressed, modulated by a piezoelectric transducer, and forced through jets onto the thermal interface. A stream of high velocity fluid droplets would be expelled from the jet nozzles (the result of the fluid resonance) and impact the thermal interface. The fluid droplets would absorb the latent heat of the surface and experience a phase transformation, where they would be converted to vapor. This vapor could be allowed to expand through a tesla turbine and through a heat exchanger. The vapor would condense as it passed through the heat exchanger and be transformed back to a fluid. The cooled fluid would then be compressed and the cycle would continue.
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Old 8th April 2010, 01:15 AM   #20
wakibaki is offline wakibaki  United Kingdom
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Quote:
Originally Posted by thadman View Post
The cooled fluid would then be compressed and the cycle would continue.
Compressed fluid?

Outstanding.

Compressed fluid is like hen's teeth. You wouldn't believe how many arguments I could win if I could only get hold of some compressed fluid.

w
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