Re: [Amps] 8877 amp- to ground fil ct or not?

[Steve <g8gsq72@gmail.com>]

There's no actual need for a CT on the heater transformer winding on an 
indirectly heated tube.
If you connect the cathode to one side of the heater, you certainly 
don't want to ground the CT on the heater winding.
Steve

> 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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