Re: [TCML] 3-500Z tube coil project

[futuret@xxxxxxx]

Jason,

Your design seems OK I think.  I tried a 3-500Z a few times in a VTTC, 
but it was back when I was just learning about VTTC's.  I got 17" sparks,
but longer sparks should be obtainable.  

If you need tighter coupling, you can usually raise the primary slightly,
so that the bottom of pri is higher than the bottom of the secondary.

I think there are two types of 3-500Z, one has a graphite plate, the other
a sheet metal plate.  I would assume the graphite plate can handle more
power, although the spec sheets might not suggest that.

My website is:     http://futuret.110mb.com   

There's a menu there leading to my VTTC pages.

John

 

 


 

 

-----Original Message-----
From: Jason Johnson <jasonmsusolar@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, Jul 13, 2010 8:11 pm
Subject: [TCML] 3-500Z tube coil project


So I have recently acquired a 3-500Z, supposed to be a working tube pulled

from service.



I have been collecting parts to build a VTTC with the tube, but have not

fully decided on all of the parameters and was hoping to gain some insight

from others more familiar with tube coils (like any of the folks with great

tube coil websites and/or youtube vids...).



So far I'm planning:

- 3.5" x 18" secondary, wound with 25 gauge magnet wire;

- 2.75" x 6" toroid;

- 6.625" outside diameter primary coil form;

- 22 turn primary, wound with 10 gauge magnet wire and tapped every 1/3 turn

or so starting at turn 16;

- 24 turn grid coil (or at least starting around there and tweaking as

necessary...);

- 1.42 nF 20 kV doorknob (high quality N4700 type) in parallel with a 7-500

pF 15 kV vacuum variable for the tank cap;

- 2200 VAC MOT level shifted with 2.4 uF;

- Standard filament transformer, fans, bypass caps, etc.



I haven't decided on grid leak components yet, my thoughts on that are kind

of as follows...



According to the spec sheets, the 3-500Z is very similar in overall ratings

to the popular 833A tubes with one exception - the amplification factor is

130 instead of 35...making this a fairly high mu power triode in comparison.

So I'm thinking that the grid leak capacitor should start out at about 1 nF

(on par with some 833 coils) and the grid leak resistor should be about 3k

(lower than what is typical on the 833 coils).



Is my thinking correct here, or is this off base for some reason? (I'm

planning on using a rheostat in the grid leak circuit as well, since I will

likely not get the best value on the first try anyway...). Also, I'm

wondering about the tank cap size. I've got more capacitors and could try a

range of values larger or smaller than this, but I was thinking 1.7 nF or

would be a good place to start with this particular tube.



Finally, how far do I want to be able to adjust the coupling? If I close

wind the 10 gauge wire, I don't think that I can achieve a k value of more

than 0.22 or so. Does this matter? Coupling in a VTTC can often be higher

than this from what I have gathered (maybe 0.31 or so). Of course it is

simple enough to space wind a bit and increase k, but how far is necessary

I'm not sure...



The main reason that I ask the above questions is the fact that although I

have seen the 3-500Z listed as a potentially good tube for a VTTC, I have

not come across any actual examples of this tube being used to drive a Tesla

coil.



Thoughts, comments?



- Jason

_______________________________________________

Tesla mailing list

Tesla@xxxxxxxxxx

http://www.pupman.com/mailman/listinfo/tesla


 
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla