Re: Tap tunable secondary

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

Terry; This is a common problem with radio transmitters. Usualy the
secondary is wound with space winding for a frequency above the max point
and tuned down to the disired frequency with high voltage capacitors. the
taps must be well insulated to prevent arcing. You could do this on the
ground end of the coil with the primary above the tapp windings to allow
tuning.The variable cpacitors I used years ago had 3/4 in spacing between
plates with plates as big as a coffee can lid. You could do this with tapps
and jumpers if you avoid shorted turns on the open end winding.
  Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Fri, 28 Dec 2001 22:07:36 -0700
> To: tesla-at-pupman-dot-com
> Subject: Tap tunable secondary
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Fri, 28 Dec 2001 22:15:14 -0700
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi All,
> 
> I am having problems tuning my CW coil.  It is run off a variable frequency
> 900 watt, 325 to 375 kHz, industrial plasma power supply.  I can wind
> matching transformers on big 3C8 cores to fix input impedances, but the
> frequency is a problem.  It has a master oscillator frequency control so it
> does not track with fancy feedback, PLLs or anything like that.  But I can
> adjust the frequency by hand.
> 
> The problem is the secondary frequency.  If I place different top loads on
> it (like the power arc tonight) It tends to drop the optimal resonant
> frequency too low and I can't get to the optimal frequency given the power
> supply's range.
> 
> So I was thinking of making a new secondary with tap points on it so it
> could be taped at different frequencies.  About 5 inches on one end will
> have a bunch of wire loops coming out.  I don't know if it would be best to
> put these taps at the top or bottom of the coil.  I am worried about
> autotransformer action and other problems with the unused windings.
> 
> Any thoughts on this are welcome.  I don't remember anything like this
> being discussed before but maybe the long time tube coilers have run into
> this and have some ideas.  I want to pump the full 900 watts forward (plus
> 250 reflected if needed) into a power arc to see if I can make the sparks
> Richie got.
> 
> Cheers,
> 
> Terry
> 
>