[Milsurplus] PA Tank Circuit Padding Capacitors

[Bruce Gentry]

On 8/1/16 10:41 AM, Bruce Gentry wrote:
> If space is a problem and the coil is air core or on a hollow core, 
> how about adding a ferrite slug to bring the frequency down?
>
>     Bruce Gentry KA2IVY
>
> On 8/1/16 8:49 AM, AKLDGUY . wrote:
>> You say, "Padding across the coil..." so I assume you want to connect 
>> the capacitor that way and not from plate to ground (which would 
>> double the capacitor's voltage rating because the DC plate voltage 
>> would then be across it too).
>>
>> So with the capacitor across the coil (not subjected to B+), the peak 
>> RF voltage across it is approximately the plate voltage. If this 
>> final stage is AM modulated to 100%, the figure must be doubled, so 
>> the rating must be at least 700V, and should be conservative, since 
>> the voltage rises steeply when the load is not matched during tuneup.
>>
>> This info is based on information in the ARRL Handbook, 1963, p.167.
>> I would go with a ceramic capacitor, 3 KV rating.
>>
>> 73 de Neil ZL1ANM
>>
>>
>> On Tue, Aug 2, 2016 at 12:15 AM, David Stinson <arc5 at ix.netcom.com 
>> <mailto:arc5 at ix.netcom.com>> wrote:
>>
>>     Given: Series-feed Triode PA tank with link-coupled output.
>>     350 VDC B+, about 9 W out on 75 Meters.
>>     Padding across the tank coil with a 50 pFd doorknob was
>>     successful in lowering its resonant point, but space is severely
>>     restricted and doorknobs can be expensive. *Rewinding the coil is
>>     not an option.*
>>
>>     What other types and specifications of  available
>>     capacitors would you recommend for this service?
>>
>>     TNX OM ES 73 DE Dave AB5S
>>
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