ORIGINAL MESSAGE: (may be snipped)
On 4/22/2014 9:09 AM, Jim Garland wrote:
Hum rejection (also pointed out
by a commenter) would seem to me to be worse in low V/high I filaments,
since the induced hum field would be greater.
REPLY:
There is another issue too: With a directly heated cathode (filament),
there is an unintentional bias across the filament. Whether using AC or
DC, one end of the filament will be more negative than the other and
that adds a grid-cathode bias to the equation. With DC the bias is
constant, with AC it alternates of course. More anode current will be
emitted from the negative end and less from the positive end.
I don't know if this causes any actual harm, but I can't imagine it
helping any.
73, Bill W6WRT
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