[Amps] arc to grid basket TSPA

[John T. M. Lyles]

The anode at the top may be a flat surface, at the 'dead head' 
region, like the inside of a metal can. At the bottom of the tube, 
there are edges of the anode and the fil/grid connections may have 
other attachments and sharp edges (like a getter assembly on 
filament). I see no reason to question why it wouldn't arc here just 
as easily as up at the top where the anode/grid may have smoother 
contours.

73
john K5PRO


>Message: 8
>Date: Wed, 26 Jul 2006 14:08:44 -0700
>From: R L Measures <r at somis.org>
>Subject: Re: [Amps] flash arcs
>To: "Tom W8JI" <w8ji at w8ji.com>
>Cc: amps at contesting.com
>Message-ID: <499C6EB0-B570-43FE-88F2-745E616FBCDA at somis.org>
>Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>
>
>On Jul 26, 2006, at 4:12 AM, Tom W8JI wrote:
>
>>
>>>  According to Gossling's paper in the Journal of the IEE
>>>  (which means it was certainly peer reviewed!), flash arcs
>>>  is slightly affected by residual gas: the 'clean up'
>>>  effect of the arc can lower the flashing voltage. He
>>>  recommends series resistance in the anode supply (now
>>>  where have we seen that recommended!) but says that it
>>>  isn't generally pracitcable with valves over 10kW. He
>>>  comments that the 'most general visible after effect is
>>>  widespread tree like markings on the grid and filament
>>>  supports. The fine wires in the active part of the grid
>>>  are, however, never damaged.'
>>
>>  That's exactly the type of damage I have seen. As I posted
>>  earlier, 3-500z's generally mark the grid support cone at
>>  the bottom with very fine lines.
>
>Since the top of the grid cone is closer to the anode than the bottom
>is, why wouldn't the arc take place at the shorter distance?