[Amps] Doorknob quality

[Edward Swynar]

On 21st February, Evert wrote:

"...When using doorknob capacitors for RF tuning circuits, is there
something special I should aware of?"

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Hi Evert,

Do not assume that merely because a capacitor like this may be rated for
some 20-KV, it does NOT mean that it will be stable & suitable for use in a
final pi-tank network...!

I learned that the HARD way with my homebrewed amplifier here: as I keyed
the rig, my RF output would slowly drop---and the plate / grid currents
would (naturally) be all over the place.

I ended-up REMOVING every single ceramic / mica padder that I had, and
instead, installed a combination of fixed junk-box vacuum capacitors, &
pre-set air variable capacitors, in both the plate tuning side of the tank,
as well as the loading side.

What has a more stable dielectric than either air, or a vacuum, right...?

If you have the room in your rig, I'd say take that route: with the
exception of fixed vaccum capacitors, it'll probably be a lot cheaper than
having to buy those expensive high current door knobs, anyway! It certainly
did the job for me here...

~73~ Eddy VE3CUI - VE3XZ