At 08:29 AM 12/11/97 -0800, you wrote:
>
>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...
>
The paper is unsigned. I got it along with a stack of Eimac Service Bulletins.
I got them from Reid Brandon. You might ask him who wrote the paper. It did
state that the voltage involved in the glitch through a tube is 50 volts. That
means that in a 4000 volt supply, the glitch resistor will have 3950 volts
accross it. The paper goes on to explain why the 3-500Z and 8877 grids and
cathodes must be limited to a < 4 Joule fault. If you cannot get the paper,
I will copy it and send it to you. Call Reid for it first; I know you will
not be happy until the author is revealed.
The bottom line is that the fine wires in the grid and cathode structures in
the above mentioned tubes should be limited to 4 Joules max. This also assures
protection to the other more robust components in the RF deck.
(((73)))
Phil, K5PC
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