SV: [AMPS] Inrush Current

[measures]

>I have heard of at least three ALPHA amps that had 8877 broken filaments.

As have I.  Curiously, in addition to the open heater, the insulation 
between the heaters and the cathode had broken down.  To me, this 
possibly suggests a B+ to gnd flashover that drove the cathode to a high 
potential.  .   

>Maybe the 8877s had this problem only during a short period? 

The problem seems to be not confined to a short period.  .  .  In my 
opinion, it is not good engineering practice to gnd one side of a heater 
when the cathode is driven.  To avoid the possibility of heater cathode 
breakdown, connect the cathode to one side of the heater, ground neither 
side of the heater, and use a RF choke.  

> Maybe this
>problem has has not been mentioned  by EIMAC  in the 8877 data sheet edition
>Rich is reading but in an earlier edition? 

Early as well as late editions of the specs mention nothing about 
limiting 8877 inrush current. 

> ...

cheers, Hans

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


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