Hi , guys.
A quick look in the Will Orr's radio bible shows that in a 160 meters
amplifier the RF choke is about millihenry! (23rd edition, page 17-5).
This is the reason commercial amplifiers use chokes made of stacked pie
wound chokes of decreasing value with the higher reactance farther from the
anode connection. since each section has a different resonance frequency,
there is hope that one of them will present a sufficient reactance at any
given frequency. One possible solution is to dispense with the parallel feed
and switch over to series feed, whereby the plate supply is connected to the
tube through the tuning inductance. The output can be taken from a link on
the inductor. Another forgotten solution is to place the feed choke at the
50 ohms end of the pi network. With 50 ohms in parallel the Q is lowered so
much as to become insignificant and the frequency covered without series
resonances is broadened accordingly.
BTW, what Ohmite did was actually to place resistance in series with the
coil. While a lowering of the unloaded Q resulted in the same kind of
reactance getting flatter, it also introduces losses which can be quite
sizeable at high power operation.
BE CAREFUL!
Alex 4Z5KS
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