I agree with Bill. There’s no problem grounding the CT of the filament
xfmr (and bypassing the fil leads at the tube socket), but I prefer
keeping the cathode isolated, and dedicated to the B- return. You
don’t want to ground the cathode, except to monitor grid current.
73,
Jim
Sent from my iPhone
> On Jun 6, 2018, at 10:54 AM, Bill Turner <dezrat@outlook.com> wrote:
>
> ------------ ORIGINAL MESSAGE ------------(may be snipped)
>
>> On Tue, 5 Jun 2018 13:08:14 -0700, N6CFH wrote:
>>
>>
>> Asking for current thoughts on grounding the filament CT on 8877. Have seen
>> both ways utilized.
>>
>> How about connecting cathode to one filament lead? Again, have seen it both
>> ways.
>
> REPLY:
>
> As you say, both ways work so I believe the best practice is to leave
> the heater "floating" i.e. not connected to the cathode. This avoids
> the need for a bifilar choke in the heater leads in a cathode driven
> (grounded grid) design.
>
> The only drawback to this is the possibility of the tube developing a
> cathode to heater short which would disrupt the input impedance, to
> say the least. The 8877 has plenty of insulation between the cathode
> and heater and this should never be a problem.
>
> 73, Bill W6WRT
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