[AMRadio] Screen Modulated 813

John Lawson jpl15 at panix.com
Mon Dec 11 12:50:51 EST 2006

On Mon, 11 Dec 2006, david knepper wrote:

> Zirconium getters best at about 1000 degrees C, this why large metal anode 
> transmitting tubes like the 4-400A, 4-1000A, and 3-500 must be operated with 
> a dull red to red anode color.  Zirconium also releases some gasses and

> You can do what you will but I like to run a little color on my large 
> bottles.

   You're making the same point I am, Dave: "visible plate incandescance" 
can be 'optimum' - 'acceptable' - 'acceptable for x-time' - 'not 
recommended - or 'disastrous'. It's device-dependent!

   All of it is a matter of physics, physical electronics, metallurgy, and 
the well-known, well-documented aspects of thermionic device design and 
contruction. It is not so much a matter of desire or personal inclination, 
as it is: at the operating point you have set for the particular device in 
use - is it within the manufacturer's ratings for that service?  If the 
plate shows visible color, so be it. If, on the other hand, a noticeable 
blush means the tube is exceeding it's design-spec, then some consequences 
will come from that... "good" or "bad" I cannot say.  If an expensive 
power tube has it's useful life cut in half, or more, from 'abuse' - 
especially if it's a fairly 'rare' type - well then....

   Dat wuz all I wuz tryin' t' say.

    Cheers  and Best of the Season!


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