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
>>
>>
>
>
>
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