I don't know why most manufacturers wont use them but I did see one that did, I
just forget who. Who is using those now? A good while back we discussed
something similar when I mentioned using bypass caps with built in spark gaps.
That would be another alternative. They use them all the time to protect CRT's
in some monitors, and used to in a lot of the older TV sets. I think Cera-mite
has these in their line.
Will
*********** REPLY SEPARATOR ***********
On 3/5/05 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. The discharge tube insures the cathode stays no
>more than the gaps voltage rating above ground potential during a HV arc to
>cathode and will fire long before a "glitch diode" will turn on and
>conduct.
>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
>> >
>
>
>
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