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Re: Size of secondary, freq, and pri. surge impedance
---------- Forwarded message ----------
Date: Sun, 12 Oct 1997 21:57:05 -0500
From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Size of secondary, freq, and pri. surge impedance
> Date: Sun, 12 Oct 1997 11:56:01 -0600 (MDT)
> To: tesla-at-pupman-dot-com
> Subject: Size of secondary, freq, and pri. surge impedance
> From: Tesla List <tesla-at-pupman-dot-com>
>
>
> ---------- Forwarded message ----------
> Date: Sat, 11 Oct 1997 20:06:36 -0400 (EDT)
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Size of secondary, freq, and pri. surge impedance
John Freau wrote:
<snip>>
> John Freau
>
> P.S. I bought a 4-400A vacuum tube at a hamfest, and it gave a
> proper 13" spark when installed in one of my tube coils. But the
> next time I turned on the coil, it gave only 9" of spark, then the
> next time, only 7", now it's down to 6". When I install my original
> good tube, the spark goes back to 13", so it must be the tube
> that is changing, not the coil. I've never seen this mode of tube
> degeneration, any ideas, anyone?
John,
I would bet money that your problem is the first number 4 in 4-400A.
If this was a 3-400A we probably would have been spared this post and
query. Around my place any big toobz that have
part numbers that start with 4 - end up collecting dust (anyone
interested in an Eimac 4CX15,000D?). Large transmitting tetrodes are most
often not happy at all operated as triodes with grids tied together, etc. This is
not just my own noise, this is learned information gleaned from correspondence
with a bonified toob engineer at Eimac Corp. I guess this is why people
like Eimac also make triodes (since they *do* seem to work better in circuits
that call for them).
Your screen grid might have been overheated and as a result of the
permanently changed metalurgy will now be trying to compete with the
cathode for the emission award.
Triode wiring of small tetrode and pentode vacuum tubes of the *receiving tube*
size (and I consider tubes like 807 definitely in this size range, and tubes
like 813 not far removed) seem to survive under triode wiring schemes
because these toobz just don't have to deal with much power in the
first place, and power is after all what causes most of the known damage modes
to thermionic tubes.
Next time your high power whatever circuit calls for a triode, ding!
(light coming on now), I'll bet it wouldn't hurt to try a triode! : )
Yeah, I know this just ain't fair to those of us that survive mainly
on adapting surplus *whatever* to work in applications never intended
by the manufacturer, like you and me both John. Sometimes physics
gets in the way of wonderful plans and you and I just can't win.
rwstephens