----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: <craxd1@verizon.net>; <amps@contesting.com>
Sent: Friday, July 21, 2006 2:28 PM
Subject: Re: [Amps] Grid fuses (was: Life and gain of 3-500Z)
Snip
> 2.) During an arc or anode to grid fault, the tube has
> plasma or significant leakage path inside. Opening the grid
> does not instantly make that plasma or path open. This is
> especially true when a very poor fuse like a small resistor
> is used to interrupt a few kV of voltage.
>
> Surely you can see all that?
"I" can Tom but is that the end of the story?.
For 3-500 factory or kit built amps, whether it be a fuse, resistor or the
original inductor at the grid that takes a HV-grid event (via a glitch
resistor) it will blow open.
Been there, read the book, seen the film and got the T-shirt.
But once the grid 'return' is gone, as you said, the plasma will still be
around.
This, surely, will the make the grid rise (positive), fully saturating the
tube, valve, bottle thereby shunting HV to ground via the cathode, blowing
the primary protection.
What damage to the grid (the most delicate electrode) occurs during this
'event' <might> be less with the above devices fitted (select your
preferred order) rather than tying the grid to ground with a solid strap.
I use R's, I've got 1985 full o/p 3-500's, once in a while there's 'pop', I
swear, fit new R's, a fuse and am back on the air in 15 minutes with the
same bottles.
Love it, the pause gives my ears and what's left of my brain a break from
the hubbub..
YMMV
Roj
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