Re: 500W Tube Coil Takes Off!

To: tesla-at-pupman-dot-com
Subject: Re: 500W Tube Coil Takes Off!
From: Tesla List <mod1-at-pupman-dot-com>
Date: Wed, 15 Oct 1997 14:43:22 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Wed, 15 Oct 1997 16:27:47 -0400 (EDT)
From: FutureT-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: 500W Tube Coil Takes Off! 

In a message dated 97-10-15 13:21:59 EDT, you write:

<< 
> Many thanks to Brent Turner, Mark Rzeszotarski and John Freau (and others
> not mentioned) for their help with my first tube coil. I ran it for the
first time
> tonight and it worked great (for a first try of course). I managed to get
> 8-10" sparks and a heck of allot of radiated RF.

Hi Jeff,

Good to hear of your successful project.
 
> The coil uses two 250TH tubes in parallel and a 0-4200 Vdc plate supply.
> The primary form is 7" dia. and the secondary is 5" dia. x 20". The primary
> caps add up to .0021uf to .0022uf (variable) and with a 22 turn primary
coil,
> resonate near 356 kHz.
 
> Question: The grid resistor, although seemingly overrated, got red hot
during
> an extended run. Since I had already adjusted it until I got the correct
plate
> current (700ma), I'm guessing that it was seeing too much voltage from the
> grid coil. I started to remove some windings from the grid coil but stopped
> after removing two, I thought I should ask the group about this first.

If the plates of the tubes don't get too red, then I would think that the
grid leak circuit is ok.  If this resistor has a sliding tab for adjustment,
and it's slid toward one end, this may make it run hotter I think.  In
general grid resistors do get hot, although it shouldn't be red hot.  
You may need a 40 watt resistor or so, maybe more.  DC operation
draws a lot more current in general than AC since the coil works on
both half cycles.
 
> Observation: Using a 10H filter choke to smooth the dc really killed spark
> output. From 8" to say, 1". Without the choke, the coil has a 60Hz (120Hz)
> hum that I really wanted to filter away. I placed the choke between the 
> center tap of the filament transformer and ground. Maybe I should move it
> to between the negative side of the full wave bridge rectifier and ground? 

I've never tried a choke in that position.  In general however, filtered DC
operation will give much shorter sparks than regular AC, usually less
than 1/3 the length, depending on how good the filtering is.  Also the
filtered DC sparks will be more like a flame, or torch, or plasma.

Toobin' and sparkin'

John Freau

 
>Jeff W. Parisse, Art Director
> Digital Design Laboratories
> www.ddlabs-dot-com
  >>
>