Acom 2000R User Manual

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BOARD which are not to be replaced by the user. Should one of these fuses be blown, it may be
indicative of other more serious failures. This is a complex and possibly dangerous operation.
For this reason we recommend this work be carried out by a trained service technician. See
the TECHNICAL SUPPLEMENT for details.
8-4. Tube Replacement
New tubes must be supplied as a Matched Pair with close electrical characteristics. Otherwise
there may be an imbalance and one of the tubes will bear an excessive share of the operating
current, which can lead to overheating and reduced tube life.
Two 4CX800A (GU74B / ГУ74Б) high performance ceramic-metal tetrodes manufactured by
Svetlana (Светлана) are employed in the amplier. Tube replacement is a complex and possibly
dangerous operation. For this reason, we recommend that this work be carried out by a trained
service technician. See the TECHNICAL SUPPLEMENT for details.
8-5. The ACOM2000A Simplied Schematic Diagram
See Fig.6-1 ACOM2000A Simplied Schematic Diagram.
The two 4CX800A (GU74B / ГУ74Б) Svetlana (Светлана) high performance ceramic-metal
tetrodes (V1 and V2) with plate dissipation of 800W each are grid-driven. The input signal from
the RF INPUT jack is passed through a broadband input matching circuit which is comprised
of components in the PHASE DETECTOR PCB and also L1, L2, C2, C3 and R1. This circuit
tunes out the input capacitance of the tubes. The resistor R1 is a termination load of this circuit
and can dissipate up to 100W of drive power.
Cathode resistors R2 and R5 create DC and RF negative feedback and equalize the gain of
the tubes. The varistor RV1 in the screen grid circuit protects the tube screen grid, and voltage
regulator in the events of a ashover.
The combinations of L3-R3 and L4-R6 in the plate circuits are the VHF/UHF parasitic suppressors.
DC plate voltage is fed through chokes RFC2-RFC3 and the capacitor C10 blocks it from the
output. The output circuit is comprised of L5-L6 and C12-C16, which form a classic Pi-L network
and suppresses harmonic frequency emissions. It is switched and tuned over the bands by
S1A-S1D and the stepping motors M3-M5 via the MOTOR DRIVER PCB. The output signal is
fed through the vacuum antenna relay K1, wattmeter current transformer TA1 and high-pass
lter RFC5-C20 and nally to the antenna output. The chokes RFC4 and RFC5 keep track of the
antenna relay contact condition and together with C20 prevent the plate supply from reaching
the antenna and RFC5 shunts it to ground if the DC blocking capacitor C10 fails. The resistor
R9 and FV1 protect the amplier from static discharge via the RF OUT connector.
The PHASE DETECTOR together with the PLATE CAPACITIVE DIVIDER, RF WATTMETER
and three OPTOSENSOR circuits are the main sources of information for the control circuit
of the amplier during the autotune process. The control circuit consists of the CENTRAL
PROCESSOR UNIT, based on the 80C31 microprocessor as the main system and the Z86E04
Zilog single chip microprocessor which is used as the antenna relay QSK controller. They are
interfaced through the INTERFACE PCB to all other circuits.
All voltages delivered from the LOW VOLTAGE and HIGH VOLTAGE SUPPLY PCBs, tube
currents, temperatures and airow cooling capability are permanently monitored. Numerous
software-derived protection limits are based on this information.
The SIGNAL FILTER PCB and RFC1 eliminate RF feedback from incoming cables, including the

Acom 2000R Specifications

General

Brand	Acom
Model	2000R
Category	Amplifier
Language	English