|[AMRadio] Re: Average Age etc..|
ne1s at neandertech.com
Tue Jul 24 12:43:04 EDT 2007
> Because When Inductive Reactance (X(l)) equals Capacitive Reactance (X(c))
> you get Resonance! At least in triodes. Pentodes need some extra work,
> due to screen voltages/current.
As far as I know, the condition of resonance: XsubL = XsubC ; holds for the
LC resonant circuit, regardless of the active element it may be connected
to, be it a pentode, tride, bipolar transistor, FET, tunnel diode, or
whatever. Of course when the LC is connected to other "stuff," the parasitic
reactances of the whole mess need to be considered and will contribute to
the "total" XsubL and XsubC which determines the resonant point.
> That brings up a question... (and I'm
> asking because I just don't know pentodes/tetrodes) should the screen
> circuit be resonant at the operating frequency, as well?
If we are considering a pentode/tetrode amplifier, the screen should be
grounded for RF (i.e., well-bypassed at the operating frequency). Exceptions
are certain oscillator circuits (modified Pierce, for example) where the
screen is actually used as the plate of the triode formed by the cathode -
control grid - screen grid, or when the screen may be used for signal
injection in a mixer circuit.
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