Re: red 304TL

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

Original poster: "S Gaeta by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sgtporky-at-prodigy-dot-net>

Hi Steve,

Yep, I meant 3KV.
This was a tube coil that a friend and I built together. He has a lot of
experience with high powered transmitters (up to 50KW, and always wanted to
build a tesla coil. I had never built a tube type coil up to that point, so
we were both "babes in the woods". The coil was so screwed up that it only
gave 8" sparks with 2.5 kv at 500 mA of plate current. He was standing 5
feet from the coil, which is a considerable distance, when he accidently
touched my grounded equipment and drew an inch long arc from his bare arm!
That really hurt!! He got more RF burns that night than he did during his
entire career as a broadcast engineer. When I noticed that the plates were
glowing orange, I yelled "Shut it off!!! The plates, the plates!!!" That's
when he told me that the plates can glow yellow if proper airflow is
installed.

After he left, I started to play around with a smaller secondary, When I
increased the coupling, and tried a slightly higher plate voltage (Just
under 3000) I only applied power long enough to look at my meters, and then
just as I glanced at the tube to see the plate color, there was a pop, and
then I saw that an arc happened inside one of the triode elements. The plate
current was 500mA, the grid was only 40ma, and the plates were showing
orange before the failure. Upon post mortem examination, there was no
discoloration, or damage to the plates, but I found a dead short from grid
to cathode. When I blast out the short with a 12 volt car battery, I can run
the tube for a few minutes, and then the same triode shorts out again. When
I shake the tube, it sounds like the grid may have broken free from a
support structure, but I can't see anything. My friend says this is a freak
accident, and not my fault, but I wondered if I might have over volted the
grid. Also, I only used a heat sink connector on the plate, but not on the
grid. I wonder if this is where I went wrong??

Eventually, I am going to drag the thing out again, and float the side of
the tube with the bad element, and experiment at half power until I get the
coil optimised, and mistakes corrected. I used a flat spiral primary, which
the tube coil experts tell me is a bad thing. I used the same basic circuit
with different component values for my 811A coil, which uses the
conventional helical primary design, and it works fine, so the primary is
probably the biggest problem with the 304TL coil.

Sue

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, November 14, 2002 8:12 PM
Subject: Re: red 304TL


 > Original poster: "Steven Ward by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<srward16-at-hotmail-dot-com>
 >
 > Hello,
 >
 > YELLOW!!!  My, my, that is really hot then!  Do you mean 3KV 900MA?  In
the
 > response you said 2kv 900ma.  By the way, what did you do to the grid?  Im
 > guessing you smoked one.  How did it happen?  Thanks for the insight!
 >
 > Steve Ward.