[AMRadio] gettering, 813s and 833s


John Lyles jtml at losalamos.com
Mon Dec 11 15:41:43 EST 2006


As Brett (N2DTS) and Gary (K4FMX) both stated, the 813 should not run with color on the plate, as they use a graphite anode. RCA stated this in their handbooks, "Plate shows no color when tube is operated at maximum CCS or ICAS ratings." 833A datasheet says "Plate shows and orange-red color when tube is operated a maximunm CCS or ICAS ratings."

Taking an 813 into the cherry is not a good idea if you want the tube to last very long. I believe that we are all in agreement on that manufacturers recommendation, now. 

This is the first i have ever heard that you want anode to be glowing in order to get better gettering action  (see below). I would be interested in knowing the source of this info. Normally in the big tubes I work with (most are 100 - 1000 kW range) we get the most outgassing when we overwork tubes, or run them at higher duty factor. This advice would seem to be limited to medium sized tubes with zirc getters then, as in the large tubes I am speaking of use a cold chemical getter inside a glass cartridge which is broken open during the final exhaust steps of manufacturing. Heat has no affect on the getter in them. Also, we use some large Eimac tubes like 4CW100,000D and 4CW250,000B and these have what I believe is a zirc getter 'flap' or 'hat'  mounted along the filament mount, which is heated only by the filament power. On these tubes, it is best to allow 15 minutes of filament only, no HV, when they have been sitting a while. Again, the getter works best with only filament heat
and full power doesn't enhance it. 

"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
absorbs other gasses at various temperatures.  The varying temperature
across the length of the anode (and as the anode heats and cools) allows the
gettering agent to absorb a wide variety of gasses.


73
John
K5PRO
Thermionic device user with a variety of industrial, scientific and broadcast applications. 



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