Good Day All,
You may recall a small thread that I helped kick-off here a few weeks back,in
the matter of using high-voltage fixed ceramic / door knob / mica capacitors as
padders in the 160-meter plate tuning circuitry of my homebrewed 2 x 813 linear
amplifier...
Based upon my own personal experience --- coupled with the comments I received
from others --- I permanently removed the padders in my set-up, & successfully
replaced them a paralleled fixed vacuum / air variable combination.
In the meantime, I've been thinking about just what specific application(s)
such capacitors might have available for them, since they're potentially so
meddlesome in the way I had used them here: are they, in essence, good only for
BYPASSING purposes...? And if so, then why would manufacturers even bother to
make variants of these things, like the "N750" units that I tried here...?
They're obviously over-rated for the likes of padding in low-powered VFO
circuits --- so what good are they, specifically...?
Now, here's the question that REALLY begs an answer: if capacitors of this ilk
are SO inappropriate for use in QRO-type applications due to internal heating,
their ity to handle excessive RF current, etc. etc., then just how appropriate
are they for use as output coupling capacitors --- i.e. the blocking cap that's
placed between the final tube(s) and the pi-network tuning circuitry...? I know
that components placed here must handle quite a load: years ago, when I built
my first amplifier (4 x 811A) I naively inserted a simple 2.5 kv (if I recall
correctly) 0.001-ufd. disk ceramic capacitor in that position --- whilst
undergoing tests with the linear, the little cap literally exploded like a
small grenade, shooting ceramic "shrapnel" all over the place!
What specific guidelines does the enterprising young (or old, for that matter)
homebrewer follow to ensure safety and longevity, both for himself AND his
creation...?
Is the door knob coupling capacitor in my amplifier yet another candidate for
some future reoplacement with a vacuum cap...?
Any & all comments based upon personal experience are hereby solicited &
welcomed...after all, "...Inquiring minds need to know!" Hi Hi
Tnx & vy
~73!~ Eddy VE3CUI - VE3XZ
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