[AMPS] parasitic suppressors

[Rich Measures]

p[[[[[[[0000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000>>Date: Thu, 11 Dec 1997 09:07:15
>>To: "Ian White, G3SEK" <G3SEK@ifwtech.demon.co.uk>
>>From: Phil Clements <philk5pc@connect.net>
>>Subject: Re: [AMPS] parasitic suppressors
>>
>>At 07:25 AM 12/11/97 +0000, you wrote:
>>
>>>
>>>Rich is obviously correct in saying that the bias zener is not in the
>>>path of a surge current loop that goes B+ - anode - grid - chassis - B-.
>>>However, what happens if the grid is connected to the chassis by a choke
>>>or resistor which then burns out? 
>>>
>>>When the grid floats, wouldn't the electron stream then switch to the
>>>cathode? That would blow the bias zener, unless something else such as a
>>>fuse blows 
>>
>You are correct, Sir.

Bias zeners also blow in amplifiers with directly grounded grids --  as 
well as in amplifiers where the grid chokes remained intact during the 
'Big Bang'.  .  As I recall, this was the case in the 3-500Z shown in the 
photograph on page 15 of the September, 1990 issue of *QST*.  The 
filament helix has somewhat obviously been bent until it touches the 
grid.  If a rauchian vanishing-gas anode/grid arc was responsible for the 
shorted zener and shorted filament, why is there no arc mark on the 
outside of the grid?  Before I opened the envelope of this kaput tube, 
the vacuum tested normal.  
... ... 
>Eimac states that an amount on energy in excess of four Joules will
>permanently damage EITHER the cathode OR the fine wire grid structure during
 > repetitive arcing in typical circuits used by amateurs. ...

The grid of an 8877 is rated at 25W dissipation.  The grid of a 3-500Z is 
rated at 20W dissipation.  The "in excess of four Joules will permanently 
damage" statement seems to be questionable.  . 
[note:  a Joule (J) is 1 watt for 1 second}  
-  For a tube whose grid is rated at 1W, 4J might possibly cause damage.  
For a tube whose grid is rated at 25W, how could 4J damage the grid?  I 
find it hard to believe that a legitimate power grid tube engineer wrote 
such a statement, Phil.  Do you know the name of the person who wrote it? 
 
  ... ... ...
Rich...

R. L. Measures, 805-386-3734, AG6K   


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm