-----Original Message-----
From: Ian White, G3SEK <G3SEK@ifwtech.com>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 18 February 2002 13:05
Subject: Re: [AMPS] gs35 internals
>
>Steve Thompson wrote:
>
>>>In more detail, please can you confirm which (if any) of the arcs has
>>>either (a) holed the grid, (b) marked the cathode underneath, and/or (c)
>>>burned the cathode?
>
>>All of the marks with the brown circumference are on the cathode
>>surface. There's heating discolouration on the grid above all but the
>>smallest one, and the merest hint of distortion in the mesh above the
>>really big spot top left. No holes in the mesh at all.
>>
>
>Thanks, Steve... very interesting. It confirms that arcs from anode to
>grid do affect the cathode underneath as well.
Brought some higher mag to bear (results remind me of how my eyesight is
failing). On the grid picture, the big spot at 11 has cratering and buckling
on the cathode. One 'link' of grid wire is missing, and one next to it has
bent in to touch the cathode (or what's left of it in that area) although
there's no dc short. The mark at 2.30 has a pinhole in the cathode surface
as well. All of the marks represent serious damage to the cathode surface.
My suspicions about it were aroused initially when the hipot showed 2kV
breakdown and heater consumption was all wrong, pulling nearly 50% too much
current when I started conditioning it. Subsequent tests with a PSU showed
that it had no emission at all. There might be interesting things to find
from further dissection. I'll cut it up if you like, or you can have it to
play with yourself.
>
>Any idea how the tube went dud? Did it ever work, or might it have been
>soft on arrival? Wonder how much HV?
Absolutely no idea at all how it died - it was like this when I received it.
Date code is 12/74. It was offered as a pull very cheaply, and replaced with
an unused one when I reported the problems, much to the credit of the
supplier.
Steve
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