Re: 3-1000z coil, more questions

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ross,
         One query and one basic explanation since I am unable 
to answer all of your questions (yet):

On 31 Jul 00, at 11:57, Tesla list wrote:

> Original poster: "Ross Overstreet" <ross-o-at-mindspring-dot-com> 
> 
> 
> I'm still working on the 3-1000z tube coil.  I have updated the schematic to
> include most of the suggestions you guys provided.  The schematic is still
> missing some RF chokes, but I'll draw them in as soon as I figure out how to
> make them.  As you can see from my tube page
> http://users.better-dot-org/roverstreet/projects/tube_coil/tube.htm, I have the
> platform complete and have started bolting things down.  Guess I'll jump
> right into the questions.
> 
> 1.  My secondary is 4" x 23 5/8", wound with 0.021" magnet wire, and has a
> measured resonant freq of 400 KHz.  (This is surprising b/c Medhurst &
> Wheeler predict it to be 375 kHz) 

How many turns are actually on it? The 0.021" is the copper 
diameter, not the outside diameter of the insulated wire.

 I have a handful of 2500pF, 30KV doorknob
> caps that I planned to use in the tank circuit.  I plan to use 12ga THHN
> wire (.135 OD) wound on a 6.25" PVC pipe for the primary.  When I started
> running the numbers, looks like I can get near 400kHz using one of the
> 2500pF doorknobs and around 18 turns in the primary.  Are these reasonable
> numbers?  Should I aim for less primary turns and more C?  More L and less
> C?
> 2.  I don't really understand what the grid-leak network is all about.  I
> have a good understanding of disruptive coils but this triode stuff is
> making me feel dumb.  It would really help me out if someone could give me a
> general overview of what is happening in the typical triode TC circuit.

That part of the circuit uses self- rectification by the grid 
to generate its own negative bias. Since the grid conducts on 
the positive half cycle of the feedback/grid tank voltage, the 
tank end of the capacitor charges up +ve wrt ground. on the 
next half cycle, the capacitor couples the negative swing to 
the grid pulling it -ve wrt ground.

Regards,
malcolm
  
> 3.  Anyone see anything terribly wrong with the schematic (other than wrong
> values in the tank circuit and lack of chokes)?
> 
> 4.  I know that the leads from the filament transformer to the tube should
> be short.  Is 2.5ft with 10ga wire too long?  I can mount it under the top
> deck right near the tube if I need to.
> 
> If I ever figure this !-at-#$ thing out I'll be sure to thoroughly document it
> on my page so others can come up to speed more quickly.
> 
> Thanks,
> Ross-O
> 
> 
> 
>