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Registered Member #1837
Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65
Hi everyone. I am an extreme newbie to tesla coils. I am an elevator constructor in NYC and work around electricity all day so I guess i could be more of a newbie, but nothing I work on is above 600V.
I want to build this coil: Looking at the schematic am I correct that the T2 transformer is a step down XFMR? 120V in with 6.3V out? I always thought i would need a step up XFMR. Also do the tubes have to be "matched". I'm not sure what this really means but i see it advertised.
My best guesses are these: -An 811a tube runs off 6.3V -the long thin winding that supports the output toroid is called a secondary and has no connection to anything but induces voltage from the L1 and L3 windings.
Do I have it right so far? If i find an MOT is it ok if it's over 2kV? How many mA should it be rated?
Sorry for all the questions but any help is appreciated. Thanks. Dennis
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Yes, T2 puts out 6.3V for the filaments of the 811As. That's what voltage the filaments need to operate properly. The MOT makes the high voltage that goes to the plates of the tubes.
The TC will work with unmatched tubes. I would think that the performance would be slightly better if they were matched though.
L1 is part of the tank circuit that supplies most of the power to the secondary. L3 is the feedback coil to switch the tubes on and off so that it can induce a voltage on the secondary. Also the bottom of the secondary is grounded. I'm not sure of which ground you can use though. I know that it isn't a very good idea to use the mains ground because it may mess with other appliances that are connected to the ground. Another option (I think is the best) is to put a metal rod into the ground and use that. There are some sites out there that can give you more information on grounding.
A MOT is usually rated for 2kV@500mA. The cheapest way to get a MOT is to open up a microwave that is going to be thrown out (doesn't have to be yours) and take out the transformer. Be careful of the MOC because the internal bleeder resistor might have failed and the cap can hold its charge for a while.
Hope this helps a bit and welcome to the 4hv forums.
Registered Member #1837
Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65
Thanks for the tips Myke. I'm going to start putting together the parts. This coil looks like it would be very inexpensive compared to others so i want to give it a shot.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just one thing to note is that MOTs are lethal, despite their small appearance. I realize you probably work around electricity much more hazardous than a little ole MOT, but don't let its small size fool you! :) They must be respective just as much as a pole transformer as they are not current limited like NSTs.
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Steve Ward dual 811A TC
