[Amps] Alpha 77Dx -Adding Grounded Grid Filament Choke

[R.Measures]

On Mar 5, 2005, at 9:54 AM, Paul Hewitt wrote:

> 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.

I would:  not ground either side of the heater supply, use a glitch-R 
to limit I-pk to 200a, and I would put a string of 20, 200a pk glitch 
diodes from the HV neg to gnd.

> Paul
>
> PAUL HEWITT
> WD7S PRODUCTIONS
> QRO HOMEBREW COMPONENTS
> http://home.earthlink.net/~wd7s
>
>
>
> ----- Original Message -----
> From: "Tomm Aldridge" <KD7QAE at ARRL.NET>
> To: "Paul Hewitt" <wd7s at earthlink.net>
> Cc: "R. Measures" <r at somis.org>; "AMPS" <amps at 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 at somis.org>
>>> To: "Paul Hewitt" <wd7s at earthlink.net>
>>> Cc: "AMPS" <amps at contesting.com>; "Paul Christensen" <w9ac at 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 at somis.org>
>>>>> To: "Paul Christensen" <w9ac at arrl.net>
>>>>> Cc: "AMPS" <amps at 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
>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>
>>
>
>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org