Hi Tomm
With the GS-35B, (cathode tied to filament internally) I would use a
filament choke and ground one side of the filament secondary, transformer
side of the choke of course. A spark gap at the cathode wouldn't hurt but
might be over-kill.
Paul
PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://home.earthlink.net/~wd7s
----- Original Message -----
From: "Tomm Aldridge" <KD7QAE@ARRL.NET>
To: "Paul Hewitt" <wd7s@earthlink.net>
Cc: "R. Measures" <r@somis.org>; "AMPS" <amps@contesting.com>
Sent: Saturday, March 05, 2005 9:45 AM
Subject: Re: [Amps] Alpha 77Dx -Adding Grounded Grid Filament Choke
> As I understand this, I really should be adding a very high speed clamp
> to ground from each of my GS35B cathode connections in the form of a
> triggered device or a spark gap. Correct? What I don't understand is
> what failure or operational modes cause thsi to happen in a well
> designed amp?
>
> Tomm
>
> Paul Hewitt wrote:
> > The gap I'm using is a Bourns 2035 series, 90 volt, 20KA (single pulse),
> > hope the glitch resistor holds !! The gap through Mouser is $3.22
single
> > piece price
> >
> > Arc to ground or internal arc to cathode, same problem for the filament.
If
> > the filament secondary is not grounded the cathode to filament breakdown
> > rating becomes 150v plus the transformer winding breakdown rating, (or
> > feed-thru cap breakdown rating, connecting wire insulation, etc). The
> > 90-150 volt spark gap still saves the filament.
> >
> > I have had unintentional spark gaps between the B- buss and ground of
.5"
> > fire,(with catastrophic results) while a 1N5408 "glitch" diode sat there
and
> > smiled at me. The spark gap is faster than the diode, race them
sometime.
> > I now use a spark gap paralleled with the "glitch diode plus a spark gap
at
> > the cathode and all is good in river city.
> > Paul
> >
> > PAUL HEWITT
> > WD7S PRODUCTIONS
> > QRO HOMEBREW COMPONENTS
> > http://home.earthlink.net/~wd7s
> >
> >
> >
> > ----- Original Message -----
> > From: "R. Measures" <r@somis.org>
> > To: "Paul Hewitt" <wd7s@earthlink.net>
> > Cc: "AMPS" <amps@contesting.com>; "Paul Christensen" <w9ac@arrl.net>
> > Sent: Saturday, March 05, 2005 8:14 AM
> > Subject: Re: [Amps] Alpha 77Dx -Adding Grounded Grid Filament Choke
> >
> >
> >
> >>On Mar 5, 2005, at 7:57 AM, Paul Hewitt wrote:
> >>
> >>
> >>>Hi Rich
> >>>For the 8877 at HF you can save the filament choke, a simple gas
> >>>discharge
> >>>spark gap at the cathode will fire long before an internal arc to
> >>>cathode
> >>>will jump to the filament.
> >>
> >>What is the peak-I rating of the gas-discharge device, the V-drop
> >>across it at the peak-I rating, and what is its cost?
> >>
> >>
> >>> The discharge tube insures the cathode stays no
> >>>more than the gaps voltage rating above ground potential during a HV
> >>>arc to
> >>>cathode
> >>
> >>The problem is not a HV arc to cathode, the problem is a +HV arc to
> >>chassis ground -- which in turn tries to elevate the cathode to the neg
> >>amount of HV. Since this is typically several neg. kV, and the max-V
> >>rating between the heater and the cathode is c, 150v, there's trouble
> >>in river city.
> >>
> >>
> >>>and will fire long before a "glitch diode" will turn on and conduct.
> >>
> >>Glitch diodes are thoroughly on at 1v per junction.
> >>
> >>
> >>>Eimac recommends this on the 8877's bigger brothers. Un-grounding the
> >>>filament secondary is a good idea also, no sense having the filament
> >>>looking
> >>>like a lower impedance path to ground than the spark gap !!
> >>>Cheers
> >>>
> >>>PAUL HEWITT
> >>>WD7S PRODUCTIONS
> >>>QRO HOMEBREW COMPONENTS
> >>>http://home.earthlink.net/~wd7s
> >>>
> >>>
> >>>
> >>>----- Original Message -----
> >>>From: "R.Measures" <r@somis.org>
> >>>To: "Paul Christensen" <w9ac@arrl.net>
> >>>Cc: "AMPS" <amps@contesting.com>
> >>>Sent: Saturday, March 05, 2005 12:55 AM
> >>>Subject: Re: [Amps] Alpha 77Dx -Adding Grounded Grid Filament Choke
> >>>
> >>>
> >>>
> >>>>On Mar 4, 2005, at 6:30 AM, Paul Christensen wrote:
> >>>>
> >>>>
> >>>>>Whoops - my mistake. The 77Dx's 8877 does not tie the cathode and
> >>>>>filament
> >>>>>together. One side of the filament is grounded. Would it still be
> >>>>>advisable to add the common-mode filament choke anyway?
> >>>>
> >>>>Not if you have a free supply of 8877s.
> >>>>- I would add a bifilar RFC, unground the filament/heater winding,
> >>>>and
> >>>>wire the cathodes to one side of the heater.
> >>>>
> >>>>>-Paul, W9AC
> >>>>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>Richard L. Measures, AG6K, 805.386.3734. www.somis.org
> >>
> >>
> >
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
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