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Forums
4hv.org :: Forums :: Tesla Coils
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Making an ultra high frequency Tesla coil...

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Inducktion
Sat Jan 16 2016, 03:50AM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
 		I ordered some parts from Mouser for this tesla coil; If the semiconductor route doesn't work properly I'll go with vacuum tubes instead.
I already have a couple of different ideas to try out, so we'll see how it goes...

edit:
Well, since I want to be prepared in case semiconductors don't work properly I've been looking at vacuum tubes.

I found a listing for 10 2C39A vacuum tubes for $27 shipped. They're air cooled transmitter tubes, and rated at 100 watts each with only 1 amp for the filament at 6.3 volts.

They're also pretty small, too. Sound like I should jump on them?
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Hazmatt_(The Underdog)
Sun Jan 17 2016, 05:42AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		You're going to need sockets and the chimneys for a forced air cooled tube. You will probably need to do a fairly involved chassis too because the fan will have to pressurize the base of the tube with the cooling air, which will be forced up through the chimney and through the cooling fins of the anode.

Me personally I would go for something a little less complicated like the 811A, a bunch of 807's (I like this one), 572B's etc. (graphite anode beastie)
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Inducktion
Sun Jan 17 2016, 05:47AM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
 		my worry with going with larger regular tubes is supplying the filament. I don't have a PSU lying around that can do the power needed to give the filament life.
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Hazmatt_(The Underdog)
Sun Jan 17 2016, 05:52AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		You can't find or wind a filament transformer?

Maybe even a beat-up ATX power supply that you can hack for 6.3V?

The filament supply is probably the easiest part of lighting the tube.

A MOT pretty much has it covered for a 572B.
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Sigurthr
Sun Jan 17 2016, 08:38PM
Sigurthr Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597
 		For the 811A you can use these: Link2

Or you can do what I do for filament supplies. Grab a 10A buck smps off of ebay and run it off a cheap chinese ac-dc 12v or 24v converter.
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Inducktion
Sun Jan 17 2016, 09:37PM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
 		Alright;
I bought a Type 803 vacuum tube for $13. Seemed like a much better deal than trying to get a 811A, plus it has higher plate dissipation.

I'll look around for a filament supply.
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Hazmatt_(The Underdog)
Mon Jan 18 2016, 04:34AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		Sounds like a good choice. You can run it hot without complicated ventilation, it has plenty of headroom on the B+ side, and lots of power handling.
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Inducktion
Tue Jan 19 2016, 12:55AM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
 		So I modified a SMPS I had lying around. It was originally rated for 5 volts at 8 amps.

I changed some resistors (and disconnected the OVP) and got an adjustable voltage from 7 to about 10.50 volts. Perfect for the 803.
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Perezx
Wed Jan 20 2016, 09:48AM
Perezx Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35
 		SSTC is almost incompatible with 20 MHz. You will just waste energy opening and closing your fet.
Try VTTC basefeed, I've described one here and it is staying close to 20 MHz.
And yes, have to mention: you wont get any streamer at this frequency. Just a bunch of flame.
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Inducktion
Thu Jan 21 2016, 02:44AM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
 		Yeah I'm realizing this. I tried making a starting oscillator at 20 mhz, and attempted to square it up with a high speed schmitt trigger.

Yeah no it wasn't happening. Still very much a sine wave and not pretty.

Guess vacuum tubes it is!
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