QRO Technologies HF-2000 Instruction Manual - page 21
21
ALC CIRCUIT
ALC Adjust Control (R13) located on the front panel allows you to set the ALC threshold to match
your Transceiver.Please refer to the Schematic and PCB drawing for the ALC/Power PCB-610.
Capacitors C606 & C607 form a voltage divider that couples some of the RF driving voltage to
Diodes D603 & D604. When the RF driving voltage exceeds the ALC threshold, the diodes rectify
the negative half cycles. Capacitor C605 filters and bypasses this voltage, while resistor R603
provides isolation. The negative voltage appearing at ALC Output connector (J5) is coupled back
to the transceiver to control its gain and reduce "flat topping" voice peaks due to overdrive. This
allows you to control the output of your transceiver without reducing your transceiver's drive.
GRID METER CIRCUIT
Grid current meter M-1 provides an indication of grid current between 0 and 300 milliamperes.
The grid current meter is connected in parallel with shunt resistor R311 located on the LV & Bias
PCB-260. The grid return circuit is through bias diodes D303 -D310, transistor Q302 to the center
tap of filament winding of power transformer T1. From this secondary winding, the grid current
flows to the filaments via the tube filament circuit.
PV (PLATE VOLTAGE) MULTIMETER CIRCUIT
When you select this function, resistors R301 - R304 located on the HV Diode PCB-110 form a
voltage divider to measure plate voltage. Resistors R302 - R304 form a series multiplier
resistance for meter M-2 while resistor R301 forms a current shunt for the meter. Diodes D311
& D312 plus capacitor C307 provide M-1 with transient protection.
IP (PLATE CURRENT) MULTIMETER CIRCUIT
When you select this function, meter M2 indicates the plate current drawn by the tubes between
0 and 1400 milliamperes. It is switched in parallel with resistors R308 - R310 located on the LV
& Bias PCB-260. The voltage drop across these resistors is measured. The meter scale is
calibrated to indicate the plate current by using the fixed parallel resistance values of R308 -
R310 and the voltage across them. Diodes D313 & D314 plus capacitor C306 provide M-2 with
transient protection.
PO (POWER OUTPUT) MULTIMETER CIRCUIT
Please refer to the Schematic and PCB drawing for the ALC/Power PCB-610. Capacitors C601,
C602, and C603 form a RF voltage divider for a portion of the RF output voltage. This voltage is
passed to a rectifier circuit consisting of diodes D601 & D602. Capacitor C604 provides filtering
and bypassing. The resulting DC voltage then passes through resistor R601 through POT R604
and to the base of transistor Q601. Q601 and its associated components form an amplifier circuit.
The resulting DC voltage then passes through multiplier resistor R606. From R606 the voltage
goes through the Multimeter which is calibrated to indicate peak output power (PEP) between 0
and 2000 watts. POT R604 allows you to calibrate the Multimeter for this function. REMEMBER,
THIS CIRCUIT DOES NOT MEASURE RMS OR CONTINIOUS CARRIER POWER. IT ONLY
MEASURES POWER OUTPUT ON VOICE PEAKS.