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Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
I have this big ~3MHz secondary and came up with this crazy idea of using an 813 and make it a plasma tweeter style VTTC. What do you think about this crazy idea, would it be possible to make it work ?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
A secondary that resonates at 3 MHz can't be 'big' can it?
Sure it can, although too big may dwarf the spark itself (I think in this case it is indeed too big) Too small secondaries tend to get very hot at these frequencies and can melt if they are wound on plastic. If it's main use is going to be audio modulation then it should be fine. But I don't think it's easy beginner project.
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
To much secondary for a little tube.
813’s really are not a good choice for first VTTC. Try an 811, 810, 833, and grid/cathode modulate. Jorrit a few post down published a nice schematic on VTTC modulation.
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
813 was all my friend had that i could borrow for this.
Btw i´ve built vttc´s before, but none used big tubes like this or very high voltage, all used EL38 and similar, with a plate voltage well below 1000V, which of course dident work very well.
But now i have a MOT and a real transm tube so i´m ready for the real thing.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Yeah, the big problem with audio-modulated tube coils is that they require quite a lot of filtering to work. If you don't want audio modulation at time you can simply use half or full wave rectified output, or level shifter.
You might want to buy a dozen electrolytic caps and series them, like 8x 220uF 400V for 27,5uF 3200V wich would suit a single mot. Depending on your tube you might want to build a fullwave doubler.
When you have such a bank of capacitors it is also very lethal and needs bleeder resistors.
I don't know how good idea it is to run a MOT with ungrounded core. I think it's better idea to run it straight from mains, ground the core and *stay away* from it. Isolation transformer will just give you false sense of security, you should not contact any part of coil while it's operating and caps charged for god's sake.
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odd and crazy tesla coil idea
