Re: Tube coils

["Stephen Carpenter" <sjc-at-xxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

On Tue, Nov 21, 2000 at 12:03:47PM -0700, Tesla list may have written:
> Original poster: FutureT-at-aol-dot-com 
> 
> In a message dated 11/20/00 9:54:26 PM Eastern Standard Time, 
> tesla-at-pupman-dot-com writes:
> 
> > Original poster: "Stephen Carpenter" <sjc-at-carpanet-dot-net> 
> >  
> >  Ive been thinking about my next coil....
> >  
> >  Thought of getting NSTs and this and that...then thought, why not try
> >  a tube coil. However...I am a bit perplexed. I have found some scematics
> >  and things, but very little good information (for an added bonus I can't
> >  check the list archives here - the website is down it seems)
> >  
> >  I noticed a couple of things...
> >  
> >  It looks like a fairly simple tube based occilator. I havn't had time to 
> >  really to a close hard look at them (its been a few years since i really
> >  read any scematics) but they are efinitly more complicated than the
> >  simple tesla coild tank curcuit.
> 
> Steve,
> 
> Tube coils are just a simple power oscillator with a tuned coupled 
> resonator as you say.  Yes, they are definitely more complicated
> than spark gap TC's.  More critical and touchy to tune and adjust also.

They seem that way. I have gotten some good info now that the pupman-dot-com
website is back up and from some of the links peopl eposted here. Thanks
everyone for the info!

I guess part of the problem is that Tubes are "old tech" and while I understand
how transistors and inductors work, nobody gives much talk about vacuume
tubes these days,

One thing I notice leads me to 2 questions.

A) None of the schematics I have seen show where the coil is tuned. Disruptive
coils (like my current broken could - transformer fried) usually have the
ability to "tap" the primary to adjust the frequency of the tank circuit.

How are they tuned? Are they normally just engineered to exacting standards
and hope for the best? None of the pictures or diagrams that I have seen 
show any way to adjust the frequency.
(oh wait...ok one of the schematics on Carl Willis' page show a tuning cap -
however, none of the others I have seen apear to have one!)

B) How does one measure the inductance (and thus figure out resonant freq) of
the coil? I knew how to do it long ago, but never did it - so I forgot. 
I also notice that the diagrams that I see usually list the frequency and
inductance. I can calculate it in theory but I can't wrap a perfect coil so
I want to actually measure it

-Steve