[Amps] 8877 Filament choke

[Gary Schafer]

>From what I remember, the cathode to filament breakdown voltage is quite low
so the cathode should be connected to the filament circuit. Should there be
a glitch a cathode choke could open and destroy the tube via a cathode
filament short.

73
Gary  K4FMX

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Bob Maser
> Sent: Thursday, November 15, 2007 5:13 PM
> To: Roger; Rick Stealey; amps at contesting.com
> Subject: Re: [Amps] 8877 Filament choke
> 
> Beats me.  I've never been on 6, not since 1961 anyway.  A lot of builders
> install a filament choke on a 8877 amp, example my Henry 4K Ultra, which
> runs a single 8877, had a filament choke.  I'm not sure about an Alpha 77.
> I have always been told that in the HF region running a 8877, you don't
> need
> one in the filament circuit but a 2.5uH choke is required in the cathode
> to
> bias line.  Bill Orr shows this in his 21st edition (1978)Radio Handbook
> on
> page 22.41.  If you don't already have some of Bill's old handbooks start
> looking for one if you're serious about amp building.
> 
> Bob W6TR
> ----- Original Message -----
> From: "Roger" <sub1 at rogerhalstead.com>
> To: "Bob Maser" <bmaser at tampabay.rr.com>; "Rick Stealey"
> <rstealey at hotmail.com>; <amps at contesting.com>
> Sent: Thursday, November 15, 2007 5:41 PM
> Subject: Re: [Amps] 8877 Filament choke
> 
> 
> >
> >
> >
> >> With an indirectly heated cathode you don't need a filament choke, in
> the
> >> HF
> >> region.
> >
> > What about when running one on 6-meters?
> >
> > Roger (K8RI)
> >
> >>
> >> Bob  W6TR
> >> ----- Original Message -----
> >> From: "Rick Stealey" <rstealey at hotmail.com>
> >> To: <amps at contesting.com>
> >> Sent: Thursday, November 15, 2007 9:26 AM
> >> Subject: [Amps] 8877 Filament choke
> >>
> >>
> >>>
> >>> Info in the ARRL handbook seems to indicate that it might be better to
> >>> not
> >>> use a filament choke on an 8877 amplifier, that it might cause more
> >>> problems than it solves.
> >>> I wonder what you guys who have homebrewed 8877s think?
> >>>
> >>> Rick  K2XT
> >>>
> >>>
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