>As I've been sorting through my 8877 filamant issue, I have noted that some
>GG 8877 designs tie the filamant and cathode together while other designs do
>not. The designs that keep the cathode isolated from the filament generally
>do not use a filament choke since what little RF that may be coupled to the
>filament can be easily bypassed to ground through judiciously placed bypass
>caps. In these designs, I have seen one side of the filament grounded and
>alternatively, designs where the filament is balanced and floating above
>ground with each side of the filament connected directly to the secondary of
>the filament transfomer.
>
>Given these design variances, is there a consenus of a preferred method?
When one side of the heater is grounded, and an inadvertent hv+ arc to
gnd temporarily raises the cathode to several kv negative, such will
cause a heater/cathode arc that can burn open the heater as the hv filter
is discharging. When the heater is not grounded, and a jumper is
connected from cathode to heater, this potential problem is avoided. The
tradeoff is that a 10a, 20 - 40uH heater choke is required.
>Is there a measured performance deficiency in the design that grounds one side
>of the 8877 filament?
No
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