John Byrns wrote:
>
> In article <48125FEF.7811EFF@[EMAIL PROTECTED]
>,
> Patrick Turner <info@[EMAIL PROTECTED]
> wrote:
>
> > I have seen glowing screen grids in tubes dear boy.
> >
> > Especially in EL34 when the screen wires have drooped a bit after
> > excessive heating traumas.
> >
> > But sometimes in badly made tubes.
> >
> > Open your eyes, use a magnifying glass.
> >
> > And the OP said the glow went away when the Ia was cut off.
> > And that happens. No Ia, and no Ig2.
>
> In my experience No Ia and Ig2 goes through the ceiling, causing a
> bright glow from the screen grid resulting in quick destruction.
Not so if the grid voltage is made negative enough.
But if the grid has a usual bias, and the anode becomes
disconnected from its load, yeah, sure, poof, the tube gets ferked in a
big way.
The OP said the Ig2 wasn't excessive at 5mA, and the "glow" he claims to
have seen
could be there or not there depending on whether the tube is cut off,
either by
negative g1 voltage, or disconnecting the B+ entirely..
But tubes with partial screen glow are not uncommon, ie, where the
screen wires are
red or orange or yellow, sometimes only partially, not all over.
When the screen all turns orange the Ig2 is always way too high.
The only thing that should glow in a tube is its cathode and heater
filament.
Seeing some sort of locally caused ****ne or superficial glow on the
internal surface of screen wires
is not something I have seen.
If the tube works with all elecrode currents correct and within spec,
and it makes the right amount of power and distortion, then its OK.
Patrick Turner.
>
> Regards,
>
> John Byrns
>
> --
> Surf my web pages at, http://fmamradios.com/
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