Vacuum Tube Tesla Coil

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I acquired a couple of old tube driven RF Amplifiers that were designed for HAM use.  I found them at a "swap meet" from a junk dealer that apparently was cleaning out the estate of an old Silent Key.  I think the call listed on the racks was K1AY.  One of the amplifiers contains a 3-1000z and the other contained a 3CX2500.  I also obtained the high voltage power supply to drive the tubes.  

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3-1000Z and 3CX2500

Bottom view of the RF Amplifiers before I took them apart

Construction Begins:

All the parts are cleaned and prepared

Initial progress.

First Light:

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1/14/00  First Light!
Managed about 10" arcs at 2200VAC on the plate and a plate current of 600ma.  
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System Overview.  Notice black hose from shop vac.  My blower caught fire during checkout so I had to substitute the shop vac dimmed down with a variac.
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1/2 sec exposure.  10" arcs.

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Top upper deck showing most of components.  Better metering is in order once I'm beyond prototype stange.  The small analog meter is plate current and the DMM is connected to a HV probe for plate voltage.
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1/4 sec exposure.   10" arcs!  This is about how the arc looks real-time.  The images are a bit blurry b/c I was holding the digicam in one hand and the deadman in the other.
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bottom_deck.JPG (83549 bytes)


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Pic of the coil with the lights on making about 14" arcs.  Exposure is 1/15 of a second.  This is a good representation of what you see realtime.
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This is an interesting pic of the coil with the lights off.  As usual, I used my Olympus C3000z digital camera.  Cam was in auto mode and chose a shutter speed of 1 sec.  Note the pretty halo on the ceiling from the tube.
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This picture shows an interesting helical structure of plasma that looks like a corkscrew.  You must view this image full size to see the effect and unfortunately the CCD in the camera still doesn't pick up quite as much light as the human eye. 

Killed it!

VTTC Model 3-1000z is DEAD.  I burned a hole in the side of the plate while driving the tube insanely beyond its ratings.  More details coming soon.  See the following pics until I have time to clean up this site.  It's a shame the tube died.  I feel like I was really understanding "best practices" in building this configuration of VTTC. 

Video of tube burning out:
Here is a short video of my VTTC making the 24" arcs. 

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First and Last Run of New system
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28" arcs shortly before the hole melted in the plate
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Hole in the plate

Rebuilt with 3CX2500

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Overview of 3cx2500 setup.  1 sec time exposure pic shows 27-28" arcs.
The voltage was about 4500VAC and I don't know plate current b/c it slams my 1A meter.  Probably 1.5-2A.
Finally made a power controller.  Nothing too fancy, just prevents powering up the plate before the filament and has a remote deadman switch  for the High Voltage.


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You can clearly see that the tube is only working during the positive half cycle

Schematic for 3-1000Z Power Oscillator wired for AC Mode Operation

Most Recent Component Values - see txt below for more complete description

VR1:  7.5K adj, 100W  C2:  5nF, 2500VDC, mica L2:  3 turns of 1/2" cu strap, 0.5" dia
C1:  3.5 nF, 30KV "doorknob" C(p):  1.2 nF +/- 0.2 nF R2:  Unknown, probably 50 ohm, 5W
C3:  9.3nF, 9600VDC, MMC L(p):   

There doesn't seem to be much on the web about VTTC design.   I think this stems from the fact that it's hard to make a canned design for VTTCs since  tubes vary so widely.  Anyway, here are a few sites with VTTC information.  

3-1000Z    Power Triode            ( The following was copied from here: )


Heater or Filament Voltage . 7.5 volts
Heater or Filament Current . 21.3 amperes
EIA Base . . . . . . . . . . F3
Prefered Substitutes . . . . None
Substitutes. . . . . . . . . None
Capacitances and Design Maximum Values

Cin . . . . . . . . . . . . 17 pf
Cout . . . . . . . . . . . . 0.12 pf
Cgp . . . . . . . . . . . . 6.9 pf
Plate Dissipation . . . . . 1000 watts
Maximum Plate Voltage . . . 3000 volts
Maximum Plate Current . . . 800 ma.
Full Frequency . . . . . . . 110 MHz

Typical Operation as a Transmitting Tube
Class of Service     Vp     Vg     Ip     Ipmax     Ig     Drive     Zl     PO
                GGB     3000     0     180     670     300     65       -     1360

A pdf of the original EIMAC datasheet was found at http://frank.nostalgiaair.orgI put a local copy here for convenience.

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