[Boatanchors] [BoatAnchors] PA Tank Circuit Padding Capacitors

[Brian]

Hello David,

I find people use the description 'series feed' to mean different circuit 
arrangements. Some would say the SCR-274-N Tx RF PA Tanks are series fed and 
the ARC-5 Txs, shunt fed. Is that what you mean?

Either way, the applied DC Voltage is NOT the DC Voltage across the 
capacitor. You need to tell us what the loaded and unloaded Q of the coil 
and capacitor will be, on resonance and off resonance. Only then can one 
reasonably calculate the safe Voltage rating of the capacitor.

For instance, in the Command Txs, look at the plate spacing of the tuning 
and padder capacitors in the RF PA circuit; they can probably withstand 2 kV 
at ground level 50% RH; at 10,000' and 80% RH, the rating would be quite 
different - but adequate for the 25 W of the ARC-5 Tx.

73 de Brian, VK2GCE.

On Monday, August 01, 2016 10:15 PM , you asked:

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