[AMPS] 8877 Rejuvination

[measures]

>
>>   Do external anode tubes have a similar problem of element outgas
>> during lengthy storage? Do they have a getter on the inner surface of the
>> anode which can be activated by arranging to raise the anode temperature?
>> I have several 8877 tubes which have been stored for several years and
>> would like to put them to use. 
>
>The gettering in the 8877 is primarily on the heat dam of the 
>heater/cathode structure.
>
>It reaches temperature from the normal heater voltage on the tube, 
>so a long period of filament activation will getter the tubes. The 
>normal problem with 8877's isn't gassing though, it is misalignment 
>in the grid causing a short or causing the grid to "hot spot" and 
>gold to be boiled off. 

See Eimac letter on my Web site.  Gold boils at thousands of degrees C.  

> Grid wires are located between bands of 
>cathode material, so the electrons miss the grid. The electric field 
>between grid wires controls anode current, so the grid normally 
>doesn't get heavily bombarded with electrons.
>
>If the grid is misaligned, areas of the grid will be struck by 
>electrons and the kinetic energy will gradually cause the gold to 
>migrate around inside the tube.
>
Not according to the letter from Eimac.  

>In severe cases, the grid may touch the cathode.   
>
... never seen here.  Flakes of dislodged strontium oxide and barium 
oxide can short between  grid and cathode.  

>....

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com