Date: Wed, 3 Aug 2011 09:18:45 -0700 (PDT)
From: Radio WC6W <wc6w_amps@yahoo.com>
Subject: [Amps] Plate Cap Quandary
I'm contemplating a single 4CX350FJ (Cout = 7pF) amplifier for 250 watts on
HF
where the plate impedance, at 2200 volts, figures to be 5000 ohms
and requires a (total) plate C circa 15pF on 10 meters,
which makes for a rather hard to find (air variable) plate cap.
So, I thought what if I take two MC325M, 1KV caps (min C. 14pF)
with the contoured plates for nicer tuning, gang the shafts, and run
them in series
resulting in a theoretical min. C of 7 pF (plus strays naturally)
Does this make sense? Has it ever been done?
Yes, I'm aware of the 1uH plate L network kluge.
Or should I just add a second tube, run twice the power at half the
impedance,
and sidestep the whole situation?
Constructive thoughts or tangential comments both welcome! :-)
73 & Good morning,
Marv WC6W
### either use 2 x tubes and double the plate current..and drop plate load Z
in half ..OR... just use a small amount of L... like .5 uh,
between plate block cap and C1 tune cap. That alone will transform the plate
load Z down to a low number... that the main PI net
can now handle. The bigger the extra L... the bigger the plate load Z redux.
The extra L can also be installed between anode and
plate block cap if you want. A vac cap will also work. Ur idea of using 2
x air caps in series will also work..albeit as long as the
sliding rotor contacts are making contact.
Later... Jim VE7RF
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