Acom ACOM2100 - MAINTENANCE; Cleaning the Amplifier; Fuse Replacement; Tube Replacement Procedure

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N O T E
After every signature listing the tube warm-up time is reset to 180 seconds regardless
of time in the OFF LINE state.
6. MAINTENANCE
6-1. Cleaning
W A R N I N G
Do not use solvents for cleaning - they may be dangerous both for you and for
the amplier paint or plastics.
Do not open the amplier. Cleaning of the amplier outer surface can be done with a piece of soft cotton
cloth lightly moistened with clean water.
6-2. Fuse Replacement
If it is necessary to replace the mains fuses, use only standard ones.
The Primary Mains Fuse(s) of the amplier are located on the rear panel (Fig. 2-1). They are of the fast
(quick blow) type, 1-1/4 x 1/4 inch Cartridge Fuses, Size "0". Use 20A for 100-120VAC operation. Use
16A for 200-240VAC operation (15A standard is also acceptable).
Besides the primary fuses, on the MAINS PCB (inside the amplier) there are three small glass fuses
(5x20mm European size): one 100mA 250VAC normal blow and two 2A 250VAC slow-blow. These
fuses should not be replaced by the user. Should one of these fuses be blown, it may be indicative of a
serious fault. A fault of this type will not occur under normal operating circumstances. Replacing these
fuses involves special skills and is inherently dangerous. For these reasons, we recommend this work
be carried out by a trained service technician.
6-3. Tube Replacement
A single 4CX1000A/8168 ceramic and metal tetrode is employed in the amplier. Replacement is a
complex and potentially dangerous procedure. For this reason, we recommend this work be carried out
by a trained service technician. Check with your dealer before attempting to replace your tube.
6-4. The ACOM1500 Simplied Schematic Diagram
See Fig.6-1 ACOM2100 Simplied Schematic Diagram. The 4CX1000A/8168 ceramic and metal radial
beam tetrode (V1) is grid-driven. It can dissipate up to 1000W when forced air cooled and is specically
designed for class AB1 RF linear ampliers.
The input signal from the RF INPUT jack is passed through a broadband input matching circuit, which
consists of components in the INPUT PCB and Rsw. This circuit tunes out the tube input capacitance.
The swamping resistor Rsw is a termination load for this circuit and can dissipate up to 100W of RF
drive power.
Cathode resistors labeled Rc create DC and RF negative feedback, thus stabilizing the gain and equalizing
the frequency response. The varistor VSsg, in the screen grid circuit protects the tube and the screen
grid voltage regulator in the event of an internal tube ashover.
The combination noted as Lp1-Rp1 in the plate circuit is a VHF/UHF parasitic suppressor. DC plate
voltage is fed through chokes RFC1-RFC2 and the capacitor Cb3 blocks it from the output. The output
circuit consists of LP1, LP2, LL, CP1-CP3, and CL1-CL3, which form a classic Pi-L network to suppress
any harmonic frequency emissions. This tank is switched and tuned by S1A-S1C and the air variable
capacitors CP1, 2 and CL1, 2. The output signal is fed through an additional VHF low-pass lter for
frequencies above 55 MHz (Lf1, Lf2 and Cf). Then it is passed through the vacuum antenna relay K1,