>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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