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Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
First of all: it works! And now some questions: - How red may the anode plate from the 811 become? - I have a couple ceramic disk capacitors, and they work well, but as Herr Zap said, they become slightly warm. What is the perfect cap (with ebay seller) for my Tesla coil? -This is the most important question! Now I use a voltage regulator trafo, a big thing, but is it possible to use a triac-regulator (ev. zero-crossing)? Then I can build eveything on the same chassis plate.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
At maximum CCS ratings, the plate should show no color, and at maximum ICAS the plate should show no more than a barely perceptible red color. So, try to keep the plate no higher than a little hotter than black.
A good choice for vttc caps are transmitting ceramic doorknob capacitors, or mica capacitors. These are rated for high currents and high frequency. If a doorknob cap is rated for alot of reactive power, eBay sellers will definately let you know. A doorknob capacitor rated for high reactive power will usually be a lower capacitance and/or voltage per unit of size than one that isn't, which definately makes sense. There are a lot of doorknobs that are type KVI-3. They may look like transmitting caps, but they are not rated for reactive power. Type k15y-1 seems to be and there are quite a few on eBay. For example: The voltage is a bit low, so it would be a good idea to put 2 in series, and then use a few strings in parallel to get the right capacitance for tuning. It may end up being large, but at least it would be a proper tank cap.
A triac regulator should work fine. I don't know if it would effect the sparks, i have never seen what the output of an iron core transformer looked like when a triac dimmer was used, but i think the output would still be semi-sine.
Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
Thank you! I think the caps must wait a bit, they are rather expensive! I am beginning to look for a circuit with a triac. I wonder if anybody has done that, a triac regulation for a micro-golf transformer.
Registered Member #2899
Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255
And while I am asking... is it advisable to make a soft-start for the filament of the 811a? And can the power be regulated with the grid-resistor? The value is now 20Kohm.
Registered Member #3567
Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260
grid leak controls how long the coil is off. The grid leak cap is negative, and if there was no resistor, it would fail to oscillate, because after that cap is negativ, it is going to be negative for a looong time. So, we use the resistor to use up that charge. Depending on how long it takes for the cap to discharge, the tube will be off for a long time. It basically controls the duty cycle, if you can think of it that way. (not really)
Registered Member #3567
Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260
not tooo much, because regardless of any resistor, because the 811a is using a few watts of driving power, and the cap is in the nf, it's only going to be negative for less than a blink of an eye. the grid leak does relate to how many turns the tickler will need.
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811a coil questions
