Theory Of Operation - Yaesu FL-2000B Instruction Manual

full scale at SWR switch "F" position. Turn SWR switch to "R" position, then SWR
may be read directly from upper scale of the meter.

THEORY OF OPERATION

The FL-2000B is designed to use two 572B/T160 zero bias triodes in a class B
grounded grid configuration.
The RF driving power delivered to the input is applied to the tube filaments through a
changeover relay and a pi-network on each band which is selected by the input
switch S2a. The input switch is ganged to the band switch S1.
The RF voltage appearing on the grid of the tube is coupled through C203 to ALC
rectifier diodes D201 and D202. The plate potential of D201 is determined by R1,
R2, R3, so that adequate automatic level control voltage is available to control the
exciter. The bias is set by R4 for 0.09 Amps idle current. In standby, the cold end of
S4 is opened so that bias voltage cuts off the tubes. The plate circuit is coupled to
the 50 ohm output load by an adjustable pi-network through the SWR bridge circuit.
SERVICING
WARNING
EXTREME CAUTION SHOULD BE TAKEN WHENEVER MAKING ANY
ADJUSTMENTS INSIDE THE CABINET. BEFORE OPENING THE CABINET
COVER, UNPLUG THE POWER PLUG FROM THE AC LINE.
Removing Top and Bottom Covers
After disconnecting the power cord from the AC line, the top cover can be easily and
safely removed by pulling up the two lock fasteners.
The bottom cover can be removed by taking out the four screws on it.
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